Publications

@article{nokey,

title = {Acorn woodpecker movements and social networks change with wildfire smoke},

author = {A.E. Johnson and S. Barve and L. Dreiss and D. Shizuka and E.L. Walters},

doi = {https://doi.org/10.1016/j.cub.2023.08.096},

year  = {2023},

date = {2023-10-09},

urldate = {2023-10-09},

journal = {Current Biology},

volume = {33},

pages = {R996-R997},

abstract = {Climate change has contributed to increased wildfires. Wildfire smoke exposes wildlife to hazards and mortality from particulate matter on a scale larger than the area impacted by fire. Using automated radiotelemetry, we illustrate how smoky conditions are associated with changes in behavior of acorn woodpeckers (Melanerpes formicivorus), a flagship species of oak (Quercus spp.) savannas of western North America. On smoky days, birds spent more time at their home territory and reduced visitation to others, especially to distant territories. Associations between birds decreased, and individuals were less assorted by group in co-visitation networks, suggesting less inter-individual coordination on smoky days. We show that between 2016 and 2020, ∼14% of the acorn woodpecker population in the US experienced fire, potentially exposing on average 89.42% of the range to atmospheric smoke annually. These findings highlight how potential effects of smoke on animal behavior may be widespread and exacerbate negative impacts of increasingly common “megafires”, even in fire-adapted ecosystems.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Territorial inheritance and the evolution of cooperative breeding in the acorn woodpecker},

author = {W.D. Koenig and J. Haydock and H.L. Dugdale and E.L. Walters},

url = {https://www.ericlwalters.org/Koenig_et_al_2023.pdf, PDF link},

year  = {2023},

date = {2023-09-23},

urldate = {2023-07-25},

journal = {Animal Behavior},

volume = {205},

pages = {241-249},

abstract = {There are two main hypotheses for why offspring in cooperatively breeding taxa delay dispersal and remain on their natal territory rather than disperse. First, ecological constraints may force offspring to remain on their natal territory until a reproductive opportunity presents itself in an otherwise saturated habitat. Alternatively, delaying dispersal and helping kin may increase an offspring's inclusive fitness. One means by which offspring might enhance their direct fitness by delaying dispersal is by inheriting breeding status on their natal territory. Such territory inheritance regularly occurs in acorn woodpeckers, Melanerpes formicivorus, a species whose social groups consist of a cooperatively polygynandrous breeding core along with nonbreeding helpers of both sexes that are offspring from prior breeding efforts. Here we examine the life-history differences and the fitness consequences of birds attaining breeder status by either inheriting their natal territory or dispersing to a new territory. Despite significant differences in life history, including the mean territory quality on which individuals bred and mean co-breeder coalition size of breeders, we found no statistical differences in either direct or kin-selected (indirect) fitness benefits for breeders that inherited and dispersed. The incidence of birds engaging in both strategies, inheriting their natal territory and later dispersing, or dispersing but later returning to inherit their natal territory, further reduces the potential direct fitness benefits of inheritance relative to dispersal, since neither precludes the other. Territory inheritance is an important, alternative means of achieving breeding status in this population. However, ecological constraints to dispersal and kin-selected fitness benefits as a helper likely play larger roles driving the acorn woodpecker's extraordinary social system.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Lifetime inclusive fitness effects of cooperative polygamy in the acorn woodpecker},

author = {Koenig, W.D. and S. Barve and J. Haydock and H.L. Dugdale and M.K. Oli and E.L. Walters},

url = {https://www.ericlwalters.org/Koenig_et_al2023.pdf, PDF link},

doi = {https://doi.org/10.1073/pnas.2219345120},

year  = {2023},

date = {2023-05-01},

urldate = {2023-05-01},

journal = {Proceedings of the National Academy of Sciences},

volume = {120},

pages = {e2219345120},

abstract = {Although over 50 y have passed since W. D. Hamilton articulated kin selection and inclusive fitness as evolutionary explanations for altruistic behavior, quantifying inclusive fitness continues to be challenging. Here, using 30 y of data and two alternative methods, we outline an approach to measure lifetime inclusive fitness effects of cooperative polygamy (mate-sharing or cobreeding) in the cooperatively breeding acorn woodpecker Melanerpes formicivorus. For both sexes, the number of offspring (observed direct fitness) declined while the number of young parented by related cobreeders (observed indirect fitness effect) increased with cobreeding coalition size. Combining these two factors, the observed inclusive fitness effect of cobreeding was greater than breeding singly for males, while the pattern for females depended on whether fitness was age-weighted, as females breeding singly accrued greater fitness at younger ages than cobreeding females. Accounting for the fitness birds would have obtained by breeding singly, however, lifetime inclusive fitness effects declined with coalition size for males, but were greater for females breeding as duos compared to breeding singly, due largely to indirect fitness effects of kin. Our analyses provide a road map for, and demonstrate the importance of, quantifying indirect fitness as a powerful evolutionary force contributing to the costs and benefits of social behaviors.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Unraveling a paradox of habitat relationships: scale-dependent drivers of temporal occupancy-abundance relationships in a cooperatively breeding bird},

author = {Natasha D.G. Hagemeyer and Mario B. Pesendorfer and Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/Hagemeyer_et_al2023.pdf, PDF link},

doi = {https://doi.org/10.1007/s10980-023-01668-0},

year  = {2023},

date = {2023-04-29},

urldate = {2023-04-29},

journal = {Landscape Ecology},

abstract = {Context



Spatial occupancy and local abundance of species often positively covary, but the mechanisms driving this widespread relationship are poorly understood. Resource dynamics and habitat changes have been suggested as potential drivers, but long-term studies relating them to abundance and occupancy are rare. In this 34-year study of acorn woodpeckers (Melanerpes formicivorus), a cooperatively breeding species, we observed a paradoxical response to changes in habitat composition: despite a reduction in the availability of high-quality breeding habitat, the population increased considerably.

Objectives



We investigated the role of annual variation in food availability and long-term changes in habitat composition as predictors of population dynamics.

Methods



Using model selection, we contrasted competing hypotheses on the effects of changing resource availability on occupancy and social group size across three spatial scales: territory, neighborhood, and landscape.

Results



The increase in abundance was largely determined by the formation of new social groups, driven by a landscape-level expansion of canopy cover and its interaction with neighborhood-level acorn abundance, indicative of long-term increases in overall acorn productivity. Group size increased with neighborhood acorn crop two years earlier but groups were smaller in territories with more canopy cover.

Conclusions



Our results indicate that scale-dependent processes can result in paradoxical relationships in systems with spatial and temporal resource heterogeneity. Moreover, the findings support the role of resources in driving changes in abundance and occupancy at a landscape scale, suggesting that colonization of marginal habitat drives the positive occupancy-abundance relationship in this cooperatively breeding species.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Fungal communities associated with acorn woodpeckers and their excavations},

author = {Jusino, M.A. and N.D.G. Hagemeyer and M.T. Banik and J.M. Palmer and D.L. Lindner and M.E. Smith and W.D. Koenig,

and E.L. Walters},

url = {https://www.ericlwalters.org/Jusino_et_al_2022.pdf, PDF link},

doi = {https://doi.org/10.1016/j.funeco.2022.101154},

year  = {2022},

date = {2022-04-11},

urldate = {2022-04-11},

journal = {Fungal Ecology},

volume = {59},

pages = {101154},

abstract = {Wood-decay fungi soften wood, putatively providing opportunities for woodpeckers to excavate an otherwise hard substrate, yet the fungal community composition in tree cavities and the specificity of these relationships is largely unknown. We used high-throughput amplicon sequencing of the fungal ITS2 region to examine the fungal communities associated with acorn woodpeckers (Melanerpes formicivorus) and their cavities in mature valley oak (Quercus lobata) and blue oak (Q. douglasii) trees in an oak savannah of central coastal California, USA. Acorn woodpeckers and their excavations harbored over 1500 fungal taxa, including more than 100 putative wood-decay fungi. The fungal communities found on the birds were more similar to those found in excavated cavities than those found in trees without excavated holes. These results suggest that symbiotic associations between acorn woodpeckers and fungi are highly diverse, with low specificity. Symbiotic associations between cavity-excavators and fungi are likely more common and widespread than previously thought.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000715217800001,

title = {Constructing social networks from automated telemetry data: A worked  example using within- and across-group associations in cooperatively  breeding birds},

author = {Daizaburo Shizuka and Sahas Barve and Allison E. Johnson and Eric L. Walters},

url = {https://www.ericlwalters.org/Shizuka_et_al_2022.pdf, PDF link},

doi = {10.1111/2041-210X.13737},

issn = {2041-210X},

year  = {2022},

date = {2022-01-01},

urldate = {2022-01-01},

journal = {METHODS IN ECOLOGY AND EVOLUTION},

volume = {13},

number = {1},

pages = {133-143},

abstract = {1. Advances in data-logging technologies have provided a way to monitor the movement of individual animals at unprecedented spatial and temporal scales. When used in conjunction with social network analyses, these data can provide deep insight into the structure and dynamics of animal social systems. Emergence of these new technologies demands concomitant progress in workflows to translate data streams from automated systems to social networks, based on biologically relevant metrics.

2. Here we outline key considerations for constructing social networks from automated telemetry data. We highlight the need for paying particular attention to the spatial arrangement of receiver stations with respect to the ecology of study system and developing appropriate criteria for quantifying associations.

3. We provide a case study for constructing social networks from automated telemetry data collected over 1 month during a study of acorn woodpeckers Melanerpes formicivorus, a cooperatively breeding bird. The data consisted of detections of known birds near receiver stations placed within core areas of group territories. We use this system to demonstrate how to build social networks to investigate biological questions about patterns of associations between group members and territory visitors across the landscape.

},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000713795600016,

title = {Are you my baby? Testing whether paternity affects behavior of cobreeder  male acorn woodpeckers},

author = {Walter D. Koenig and Anna C. B. Prinz and Joseph Haydock and Hannah L. Dugdale and Eric L. Walters},

url = {https://www.ericlwalters.org/Koenig_et_al_2021BE.pdf, PDF link},

doi = {10.1093/beheco/araa144},

issn = {1045-2249},

year  = {2021},

date = {2021-09-01},

urldate = {2021-09-01},

journal = {BEHAVIORAL ECOLOGY},

volume = {32},

number = {5},

pages = {865-874},

abstract = {Natural selection is expected to favor males that invest more in offspring they sire. We investigated the relationship between paternity and male behavior in the acorn woodpecker (Melanerpes formicivorus), a cooperative breeder that lives in family groups including offspring that remain on their natal territory, sometimes for years, and cobreeders of both sexes. Regardless of group composition, only one communal nest is attended at a time. Whereas cobreeding females share maternity equally, one male usually sires the majority of young in the group’s communal nest. Copulations are rarely observed, and thus it has not been possible to link paternity to sexual behavior. There were no differences among cobreeder males that did or did not sire young in their propensity to roost in the nest cavity at night. However, cobreeder males that attended females continuously prior to egg-laying were more likely to successfully sire young than males that did not, and the relative share of feeding visits and time spent at the subsequent nest were positively related to a male’s realized paternity. These differences in male behavior were partly due to differences among males and partly to plasticity in male behavior covarying with paternity share. Feedings by males successfully siring young also involved a larger proportion of nutritionally valuable insect prey. Males are aware of their paternity success, apparently because of their relative access to females prior to egg laying, and provide more paternal care at nests in which they are more likely to have sired young.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000687673400006,

title = {Lifetime reproductive benefits of cooperative polygamy vary for males  and females in the acorn woodpecker (Melanerpes formicivorus)},

author = {Sahas Barve and Christina Riehl and Eric L. Walters and Joseph Haydock and Hannah L. Dugdale and Walter D. Koenig},

url = {https://www.ericlwalters.org/Barve_et_al_2021.pdf, PDF link},

doi = {10.1098/rspb.2021.0579},

issn = {0962-8452},

year  = {2021},

date = {2021-08-01},

urldate = {2021-08-01},

journal = {PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES},

volume = {288},

number = {1957},

abstract = {Cooperative breeding strategies lead to short-term direct fitness losses when individuals forfeit or share reproduction. The direct fitness benefits of cooperative strategies are often delayed and difficult to quantify, requiring data on lifetime reproduction. Here, we use a longitudinal dataset to examine the lifetime reproductive success of cooperative polygamy in acorn woodpeckers (Melanerpes formicivorus), which nest as lone pairs or share reproduction with same-sex cobreeders. We found that males and females produced fewer young per successful nesting attempt when sharing reproduction. However, males nesting in duos and trios had longer reproductive lifespans, more lifetime nesting attempts and higher lifetime reproductive success than those breeding alone. For females, cobreeding in duos increased reproductive lifespan so the lifetime reproductive success of females nesting in duos was comparable to those nesting alone and higher than those nesting in trios. These results suggest that for male duos and trios, reproductive success alone may provide sufficient fitness benefits to explain the presence of cooperative polygamy, and the benefits of cobreeding as a duo in females are higher than previously assumed. Lifetime individual fitness data are crucial to reveal the full costs and benefits of cooperative polygamy.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000698981100008,

title = {Nest cavity reuse by the cooperatively breeding Acorn Woodpecker},

author = {Walter D. Koenig and Eve M. Hallock and David J. Weber and Eric L. Walters},

url = {https://www.ericlwalters.org/Koenig_et_al_2021.pdf, PDF link},

doi = {10.1093/ornithology/ukaa088},

issn = {0004-8038},

year  = {2021},

date = {2021-04-01},

urldate = {2021-04-01},

journal = {ORNITHOLOGY},

volume = {138},

number = {2},

abstract = {Although primary cavity-nesting species are capable of excavating new cavities, they often reuse old ones. To determine potential factors driving such reuse, we studied nest-cavity reuse in the Acorn Woodpecker (Melanerpes formicivorus), a cooperatively breeding species that reuses old cavities for 57.2% of nests at Hastings Reservation in central coastal California, USA. We found no evidence for significant fitness costs or benefits of cavity reuse compared to using newly constructed cavities. In contrast, several lines of evidence supported a role for constraints on both cavity reuse and on new cavity construction. The main constraint on reuse was cavities failing to survive from one year to the next, usually because the limb fell apart, filled with water, or was usurped by another species. Evidence that constraints on new cavity construction may be important included more frequent cavity reuse when groups renested and use of artificial cavities when they were experimentally provided. Nest-cavity reuse in this population appears to be driven primarily by constraints, including the energetic costs and time required to excavate a new cavity, rather than fitness consequences, even though Acorn Woodpeckers regularly excavate small holes in trees for acorn storage and the energetic costs of new cavity construction are apparently insufficient to significantly depress reproductive success. Constraints play a significant role in cavity reuse and may affect both the intraspecific and interspecific frequency of cavity reuse among facultative excavating species.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000572864600008,

title = {Tracking the warriors and spectators of acorn woodpecker wars},

author = {Sahas Barve and Ally S. Lahey and Rebecca M. Brunner and Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/Barve_et_al_2020CB.pdf, PDF link},

doi = {10.1016/j.cub.2020.07.073},

issn = {0960-9822},

year  = {2020},

date = {2020-09-01},

urldate = {2020-09-01},

journal = {CURRENT BIOLOGY},

volume = {30},

number = {17},

pages = {R982-R983},

abstract = {Although intergroup conflict is widespread in vertebrates, simultaneous agonistic interactions among several groups are rare. Acorn woodpeckers (Melanerpes formicivorus) are cooperatively breeding birds that defend acorn storage facilities (‘granaries’), which provide significant survival and reproductive benefits to breeders in the social group. Breeder vacancies in high-quality territories (i.e., large granaries accrued over multiple generations) elicit violent fights or ‘power struggles’, among multiple same-sex coalitions from neighboring groups. Here, using an automated radio-telemetry system, we found that individuals in coalitions competing for breeding vacancies — the ‘warriors’ — invested up to ten hours per day on successive days before one coalition emerged victorious. Power struggles also attracted ‘spectators’— acorn woodpeckers not eligible to fill the breeding vacancy. Apparently present only to gain social information, spectators travelled from territories as far as over three kilometers away. Our study reveals the complexity of acorn woodpecker social group networks, demonstrating the significant effort of both warriors and spectators to pursue fitness benefits and obtain social information.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000592965400019,

title = {Experimental evidence that acorn woodpeckers recognize relationships  among third parties no longer living together},

author = {Michael A. Pardo and Eric L. Walters and Walter D. Koenig},

url = {https://www.ericlwalters.org/Pardo_et_al_2020b.pdf, PDF link},

doi = {10.1093/beheco/araa079},

issn = {1045-2249},

year  = {2020},

date = {2020-09-01},

urldate = {2020-09-01},

journal = {BEHAVIORAL ECOLOGY},

volume = {31},

number = {5},

pages = {1257-1265},

abstract = {Triadic awareness, or knowledge of the relationships between others, is essential to navigating many complex social interactions. While some animals maintain relationships with former group members post-dispersal, recognizing cross-group relationships between others may be more cognitively challenging than simply recognizing relationships between members of a single group because there is typically much less opportunity to observe interactions between individuals that do not live together. We presented acorn woodpeckers (Melanerpes formicivorus), a highly social species, with playback stimuli consisting of a simulated chorus between two different individuals, a behavior that only occurs naturally between social affiliates. Subjects were expected to respond less rapidly if they perceived the callers as having an affiliative relationship. Females responded more rapidly to a pair of callers that never co-occurred in the same social group, and responded less rapidly to callers that were members of the same social group at the time of the experiment and to callers that last lived in the same group before the subject had hatched. This suggests that female acorn woodpeckers can infer the existence of relationships between conspecifics that live in separate groups by observing them interact after the conspecifics in question no longer live in the same group as each other. This study provides experimental evidence that nonhuman animals may recognize relationships between third parties that no longer live together and emphasizes the potential importance of social knowledge about distant social affiliates.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000592965400005,

title = {Acorn woodpeckers vocally discriminate current and former group members  from nongroup members},

author = {Michael A. Pardo and Casey E. Hayes and Eric L. Walters and Walter D. Koenig},

url = {https://www.ericlwalters.org/Pardo_et_al_2020a.pdf, PDF link},

doi = {10.1093/beheco/araa059},

issn = {1045-2249},

year  = {2020},

date = {2020-09-01},

urldate = {2020-09-01},

journal = {BEHAVIORAL ECOLOGY},

volume = {31},

number = {5},

pages = {1120-1128},

abstract = {In species with long-term social relationships, the ability to recognize individuals after extended separation and the ability to discriminate between former social affiliates that have died and those that have left the group but may return are likely to be beneficial. Few studies, however, have investigated whether animals can make these discriminations. We presented acorn woodpeckers (Melanerpes formicivorus), a group-living, cooperatively breeding bird, with playbacks of current group members, former group members still living nearby, former group members that had died or left the study area, and familiar nongroup members. Subjects responded more quickly to the calls of nongroup members than to the calls of current group members or former group members still living in the study area but did not discriminate between nongroup members and former group members that had died or disappeared. This suggests that acorn woodpeckers can vocally recognize both current group members and former group members that have dispersed to nearby groups and that they either forget former group members that no longer live in the vicinity or classify them differently from former group members that still live nearby. This study suggests an important role for vocal recognition in maintaining valuable relationships with social affiliates postdispersal.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000506915700001,

title = {Wandering woodpeckers: foray behavior in a social bird},

author = {Sahas Barve and Natasha D. G. Hagemeyer and Russell Winter and Samuel D. Chamberlain and Walter D. Koenig and David W. Winkler and Eric L. Walters},

url = {https://www.ericlwalters.org/Barve_et_al_2020.pdf, PDF link},

doi = {10.1002/ecy.2943},

issn = {0012-9658},

year  = {2020},

date = {2020-02-01},

urldate = {2020-02-01},

journal = {ECOLOGY},

volume = {101},

number = {2},

abstract = {In many cooperatively breeding taxa, nonbreeding subordinates, or helpers, use extra-territorial forays to discover dispersal opportunities. Such forays are considered energetically costly and foraying birds face aggression from conspecific members of the territories they visit. In contrast, breeders in cooperatively breeding taxa are expected to foray seldomly. We used novel tracking technologies to follow 62 acorn woodpeckers (Melanerpes formicivorus), a cooperatively breeding bird, to study extra-territorial foray behavior. Both helpers and breeders engaged in extra-territorial forays routinely and often several times per day. Helpers forayed earlier in the day and invested more time when foraying to high-quality territories. Unexpectedly, breeders forayed as often and as far as helpers. Breeders from high-quality territories forayed closer to their home territories than breeders from low-quality territories, reflecting a potential trade-off between foraying and territory defense. Such a routine pattern of extra-territorial forays in both helpers and breeders suggests that the motives behind forays differ by sex and social status and involve more than simply searching for dispersal opportunities.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000583814300006,

title = {Conservation and ecology of woodpeckers. Foreword to the 8th  International Woodpecker Conference Proceedings},

author = {Eric L. Walters and Hugo Robles and Dorota Czeszczewik and Utku Perktas and Gilberto Pasinelli},

url = {https://www.ericlwalters.org/Walters_et_al_2020.pdf, PDF link},

doi = {10.3161/00016454AO2020.55.1.006},

issn = {0001-6454},

year  = {2020},

date = {2020-00-01},

urldate = {2020-00-01},

journal = {ACTA ORNITHOLOGICA},

volume = {55},

number = {1},

pages = {61-62},

keywords = {invited, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000475984400001,

title = {Does Helping-at-the-Nest Help? The Case of the Acorn Woodpecker},

author = {Walter D. Koenig and Eric L. Walters and Sahas Barve},

url = {https://www.ericlwalters.org/Koenig_et_al_2019.pdf, PDF link},

doi = {10.3389/fevo.2019.00272},

issn = {2296-701X},

year  = {2019},

date = {2019-07-01},

urldate = {2019-07-01},

journal = {FRONTIERS IN ECOLOGY AND EVOLUTION},

volume = {7},

abstract = {Cooperative breeding groups often involve “helpers-at-the-nest”; indeed, such behavior typically defines this intriguing breeding system. In few cases, however, has it been demonstrated that feeding nestlings by helpers, rather than some other behavior associated with helpers' presence, leads to greater reproductive success. One prediction of the hypothesis that feeding behavior per se is responsible for the fitness benefits conferred by helpers is that there should be close congruence between the patterns of helping-at-the-nest and the fitness effects of helpers. Here we look for such a relationship in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus) in order to begin to identify the behaviors of helpers that drive the increased fitness benefits they confer. In terms of young fledged, a helper male confers approximately the same fitness benefits to a group as does a helper female; more dramatically, the effects of helper males increases with increasing food supply, most importantly the prior year's acorn crop on which this species depends, whereas that of helper females does not. These patterns do not match the nest-feeding patterns of helpers, which are greater for females than males and do not increase with a larger acorn crop the prior autumn. In contrast, the proportion of time helpers spend tending acorn-storage facilities (granaries) and are present in or near their home territory is greater for males than females and, at least for males, positively related to the size of the acorn crop. These results fail to support the hypothesis that the primary benefit conferred by helpers is feeding young in the nest; rather, they suggest that behaviors such as territorial defense and predator detection are more important. Understanding exactly what those behaviors are in this, and most other cooperatively breeding systems, remain to be determined.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000468068400008,

title = {Habitat Saturation Results in Joint-Nesting Female Coalitions in a  Social Bird},

author = {Sahas Barve and Walter D. Koenig and Joseph Haydock and Eric L. Walters},

url = {https://www.ericlwalters.org/Barve_etal_2019.pdf, PDF link},

doi = {10.1086/703188},

issn = {0003-0147},

year  = {2019},

date = {2019-06-01},

urldate = {2019-06-01},

journal = {AMERICAN NATURALIST},

volume = {193},

number = {6},

pages = {830-840},

abstract = {Joint nesting by females and cooperative polyandry—cooperatively breeding groups with a male-biased breeder sex ratio—are little-understood, rare breeding systems. We tested alternative hypotheses of factors potentially driving these phenomena in a population of joint-nesting acorn woodpeckers (Melanerpes formicivorus). During periods of high population density and thus low independent breeding opportunities, acorn woodpecker females formed joint-nesting coalitions with close kin. Coalitions were typically associated with groups with a male bias. We found strong evidence for both inter- and intrasexual conflict, as joint nesting conferred a fitness benefit to some males, a significant fitness cost to females, and no gain in per capita reproductive output for either sex. Such conflict, particularly the cost to females, may be an important reason why joint nesting is rare among cooperatively breeding taxa.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000451572800006,

title = {Causes of seasonal decline in reproduction of the cooperatively-breeding  acorn woodpecker},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/Koenig_Walters2018.pdf, PDF link},

doi = {10.1111/jav.01784},

issn = {0908-8857},

year  = {2018},

date = {2018-11-01},

urldate = {2018-11-01},

journal = {JOURNAL OF AVIAN BIOLOGY},

volume = {49},

number = {11},

abstract = {Clutch size and reproductive success decline seasonally in a wide range of temperate avian taxa. Two competing hypotheses have been proposed to explain such declines: the ‘timing’ hypothesis, which states that conditions affecting reproduction decline intrinsically with date, and the ‘quality’ hypothesis, which proposes that high-quality individuals or individuals in high-quality situations breed earlier. We contrasted the relative importance of these two hypotheses using a long-term dataset of the cooperatively-breeding acorn woodpecker Melanerpes formicivorus in central coastal California (USA). This population exhibits an 11% seasonal decline in clutch size, a 60% seasonal decline in fledging success, and a 77% seasonal decline in fledgling overwinter survival. Clutch size tracks seasonal availability of flying insects, which are a likely ecological driver of the seasonal decline in reproduction and, because of the nonlinear relationship of flying insects with date, constitute a likely factor constraining even earlier nesting. By parsing lay date data into within-female and between-female components, we found that only the within-female component had a statistically significant direct effect on clutch size, supporting the timing hypothesis. For both fledging success and overwinter survival, however, both within- and between-female effects were highly significant, with between-female effects (differences in female quality) being stronger than within-female effects. These results suggest that timing per se is a key factor affecting the seasonal decline in clutch size, but that both differences in female quality and an intrinsic seasonal decline in conditions drive the even more dramatic seasonal declines in fledging success and overwinter survivorship of fledglings.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000438492800010,

title = {Wild acorn woodpeckers recognize associations between individuals in  other groups},

author = {Michael A. Pardo and Emilee A. Sparks and Tejal S. Kuray and Natasha D. Hagemeyer and Eric L. Walters and Walter D. Koenig},

url = {https://www.ericlwalters.org/Pardo_et_al_2018.pdf, PDF link},

doi = {10.1098/rspb.2018.1017},

issn = {0962-8452},

year  = {2018},

date = {2018-07-01},

urldate = {2018-07-01},

journal = {PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES},

volume = {285},

number = {1882},

abstract = {According to the social intelligence hypothesis, understanding the cognitive demands of the social environment is key to understanding the evolution of intelligence. Many important socio-cognitive abilities, however, have primarily been studied in a narrow subset of the social environment—within-group social interactions—despite the fact that between-group social interactions often have a substantial effect on fitness. In particular, triadic awareness (knowledge about the relationships and associations between others) is critical for navigating many types of complex social interactions, yet no existing study has investigated whether wild animals can track associations between members of other social groups. We investigated inter-group triadic awareness in wild acorn woodpeckers (Melanerpes formicivorus), a socially complex group-living bird. We presented woodpeckers with socially incongruous playbacks that simulated two outsiders from different groups calling together, and socially congruous playbacks that simulated two outsiders from the same group calling together. Subjects responded more quickly to the incongruous playbacks, suggesting that they were aware that the callers belonged to two different groups. This study provides the first demonstration that animals can recognize associations between members of other groups under natural circumstances, and highlights the importance of considering how inter-group social selection pressures may influence the evolution of cognition.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000395115000013,

title = {Testing alternative hypotheses for the cause of population declines: The  case of the Red-headed Woodpecker},

author = {Walter D. Koenig and Eric L. Walters and Paul G. Rodewald},

url = {https://www.ericlwalters.org/Koenig_et_al_2017.pdf, PDF link},

doi = {10.1650/CONDOR-16-101.1},

issn = {0010-5422},

year  = {2017},

date = {2017-02-01},

urldate = {2017-02-01},

journal = {CONDOR},

volume = {119},

number = {1},

pages = {143-154},

abstract = {The Red-headed Woodpecker (Melanerpes erythrocephalus) has experienced strong population declines during the past 3 decades. Using North American Breeding Bird Survey (BBS) and Audubon Christmas Bird Count (CBC) data, we investigated 4 hypotheses that may explain this decline, including: (1) interspecific competition with native Red-bellied Woodpeckers (Melanerpes carolinus) and nonnative European Starlings (Sturnus vulgaris); (2) predation by Cooper's Hawks (Accipiter cooperii) and Sharp-shinned Hawks (Accipiter striatus); (3) climate change; and (4) changes in forested area within their range. In analyses of both the breeding and overwintering periods, our results indicated a role of increased accipiter populations in driving Red-headed Woodpecker declines through increased predation. We also found evidence for significant effects of warmer winter temperatures and increased forest cover, both directly and indirectly through their effects on enhancing accipiter populations. In contrast, our results failed to support the hypothesis that interspecific competition with either Red-bellied Woodpeckers or European Starlings has played a role in Red-headed Woodpecker declines. Despite considerable evidence for nest-site competition and aggression between Red-headed Woodpeckers and both Red-bellied Woodpeckers and European Starlings, these interactions do not appear to be limiting Red-headed Woodpecker populations.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000390334200008,

title = {A novel nest-monitoring camera system using a Raspberry Pi  micro-computer},

author = {Anna C. B. Prinz and Vikas K. Taank and Vincent Voegeli and Eric L. Walters},

url = {https://www.ericlwalters.org/Prinz_et_al_2016.pdf, PDF link},

doi = {10.1111/jofo.12182},

issn = {0273-8570},

year  = {2016},

date = {2016-12-01},

urldate = {2016-12-01},

journal = {JOURNAL OF FIELD ORNITHOLOGY},

volume = {87},

number = {4},

pages = {427-435},

abstract = {The utility, availability, cost-effectiveness, and reliability of prefabricated video systems designed to monitor wildlife have lagged behind the unique and varied needs of many researchers. Many systems are limited by inflexible video settings, lack of adequate data storage, and cannot be programmed by the user. More sophisticated systems can be cost prohibitive, and the literature describing remote wildlife video monitoring has, for the most part, not incorporated advances in camera and computer technology. Here, we present details of a pilot study to design and construct a lower cost (US $340) nest camera system to record the behavior of Acorn Woodpeckers (Melanerpes formicivorus) in artificial tree cavity nests. This system incorporates a Raspberry Pi micro-computer, Pi NoIR infrared camera, a wireless adapter to transmit video over the Internet, and Deka rechargeable gel batteries for power. We programmed the system to motion-sense, to record exclusively during daylight hours, and to automatically upload videos to the cloud over wireless Internet. The Raspberry Pi micro-computer does not require advanced programming or electrical engineering skills to build and configure and, because it is programmable, provides unprecedented flexibility for field researchers who wish to configure the system to the specific needs of their study.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000381637500016,

title = {Provisioning patterns in the cooperatively breeding acorn woodpecker:  does feeding behaviour serve as a signal?},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/Koenig_Walters2016.pdf, PDF link},

doi = {10.1016/j.anbehav.2016.06.002},

issn = {0003-3472},

year  = {2016},

date = {2016-09-01},

urldate = {2016-09-01},

journal = {ANIMAL BEHAVIOUR},

volume = {119},

pages = {125-134},

abstract = {Acorn woodpeckers, Melanerpes formicivorus, are cooperative breeders in which social groups consist of both nonbreeding helpers at the nest (offspring from prior reproductive attempts) and cobreeders of one or both sexes (usually siblings or a parent and his/her offspring). Regardless of composition, groups generally have one nest at a time at which all individuals participate in provisioning offspring. We tested the hypothesis that provisioning behaviour serves a signalling function used to gain social advantages within groups by enhancing dominance or social prestige, or by reducing the likelihood of being expelled from the group (‘pay-to-stay’). We found that birds adjusted their provisioning behaviour based on the activities of other group members by clumping their visits and by alternating their visits with other group members, thus synchronizing and coordinating provisioning within groups. Despite this evidence that acorn woodpeckers respond to the provisioning behaviour of other group members, analyses of feeding rates and patterns of overlap revealed no support for the hypothesis that provisioning functions as a signal to other group members in any of three ways: breeder males signalling to breeder females to increase their probability of mating; helpers signalling to other helpers to enhance their dominance or social prestige; or helpers signalling to breeders to reduce the probability that they will be considered ‘lazy’ and be evicted from the group. Our results add to previous studies that have thus far failed to support a signalling function for provisioning behaviour in avian cooperative breeders.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000363484700015,

title = {Temporal variability and cooperative breeding: testing the bet-hedging  hypothesis in the acorn woodpecker},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/Koenig_Walters2015.pdf, PDF link},

doi = {10.1098/rspb.2015.1742},

issn = {0962-8452},

year  = {2015},

date = {2015-10-01},

urldate = {2015-10-01},

journal = {PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES},

volume = {282},

number = {1816},

abstract = {Cooperative breeding is generally considered an adaptation to ecological constraints on dispersal and independent breeding, usually due to limited breeding opportunities. Although benefits of cooperative breeding are typically thought of in terms of increased mean reproductive success, it has recently been proposed that this phenomenon may be a bet-hedging strategy that reduces variance in reproductive success (fecundity variance) in populations living in highly variable environments. We tested this hypothesis using long-term data on the polygynandrous acorn woodpecker (Melanerpes formicivorus). In general, fecundity variance decreased with increasing sociality, at least when controlling for annual variation in ecological conditions. Nonetheless, decreased fecundity variance was insufficient to compensate for reduced per capita reproductive success of larger, more social groups, which typically suffered lower estimated mean fitness. We did, however, find evidence that sociality in the form of larger group size resulted in increased fitness in years following a small acorn crop due to reduced fecundity variance. Bet-hedging, although not the factor driving sociality in general, may play a role in driving acorn woodpecker group living when acorns are scarce and ecological conditions are poor.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000358788000016,

title = {Tree community shifts and Acorn Woodpecker population increases over  three decades in a Californian oak woodland},

author = {Devin E. McMahon and Ian S. Pearse and Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/McMahon_etal_2015.pdf, PDF link},

doi = {10.1139/cjfr-2015-0035},

issn = {0045-5067},

year  = {2015},

date = {2015-08-01},

urldate = {2015-08-01},

journal = {CANADIAN JOURNAL OF FOREST RESEARCH},

volume = {45},

number = {8},

pages = {1113-1120},

abstract = {Forest communities change in response to shifting climate, changing land use, and species introductions, as well as the interactions of established species. We surveyed the oak (Quercus L. spp.) community and Acorn Woodpecker (Melanerpes formicivorus (Swainson, 1827)) population within 230 ha of oak forest and savanna in central coastal California in 1979 and 2013 to assess demographic changes over a timescale relevant to mature oaks. Overall, percent canopy cover increased, particularly where coast live oak (Quercus agrifolia Née) and California black oak (Quercus kelloggii Newberry) were most abundant. The density of stems of Q. agrifolia increased, whereas the density of stems and basal area of valley oak (Quercus lobata Née), a species favored by Acorn Woodpeckers, decreased. The number of Acorn Woodpeckers and woodpecker territories increased over the study period, coincident with the increase in percent canopy cover; however, these increases were not related spatially. Instead, increased acorn production associated with broad-scale canopy growth likely more than compensated for the loss of Q. lobata. Our findings suggest that forests in this area are becoming denser and savanna is becoming more open, which so far has supported an increase in the Acorn Woodpecker population, despite potential habitat loss if Q. lobata continues to decline.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000350963900008,

title = {What we don't know, and what needs to be known, about the cooperatively  breeding Acorn Woodpecker Melanerpes formicivorus},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/Koenig_Walters2014.pdf, PDF link},

doi = {10.3161/173484714X687091},

issn = {0001-6454},

year  = {2014},

date = {2014-12-01},

urldate = {2014-12-01},

journal = {ACTA ORNITHOLOGICA},

volume = {49},

number = {2},

pages = {221-232},

abstract = {The Acorn Woodpecker Melanerpes formicivorus is one of a small number of woodpecker species that are cooperative breeders, living in family groups of up to 15 individuals of both sexes and all ages and exhibiting a complex mating system involving multiple cobreeders of both sexes (polygynandry). Although much has been learned concerning the social organisation and ecology of this species, over 45 years of research at Hastings Reservation, central coastal California, USA, has left us with a large number of unanswered questions ranging from relatively minor issues such as why adults have white eyes and why juveniles have a plumage similar to adult males to more major issues such as how cavity limitation could act as a driver of their unique social behaviours and how brood reduction is adaptive. Here we briefly discuss some of these questions and speculate as to how they might be addressed by future work. Long-term studies are important as a means of addressing many demographic and behavioural questions, but are even more valuable as a means of generating new questions that would have been overlooked without detailed knowledge of natural history and general ecology.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Book Review: Woodpeckers of the World: A Photographic Guide},

author = {Walter D. Koenig and E. L. Walters},

url = {https://www.ericlwalters.org/KoenigWalters2014.pdf, PDF link},

year  = {2014},

date = {2014-05-01},

urldate = {2014-05-01},

journal = {Journal of Field Ornithology},

volume = {85},

pages = {435-436},

keywords = {book review, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000316407400042,

title = {Cooperative Breeding and Long-Distance Dispersal: A Test Using Vagrant  Records},

author = {Caroline L. Rusk and Eric L. Walters and Walter D. Koenig},

url = {https://www.ericlwalters.org/rusketal2013.pdf, PDF link},

doi = {10.1371/journal.pone.0058624},

issn = {1932-6203},

year  = {2013},

date = {2013-03-01},

urldate = {2013-03-01},

journal = {PLOS ONE},

volume = {8},

number = {3},

abstract = {Cooperative breeding is generally associated with increased philopatry and sedentariness, presumably because short-distance dispersal facilitates the maintenance of kin groups. There are, however, few data on long-distance dispersal in cooperative breeders—the variable likely to be important for genetic diversification and speciation. We tested the hypothesis that cooperative breeders are less likely to engage in long-distance dispersal events by comparing records of vagrants outside their normal geographic range for matched pairs (cooperatively vs. non-cooperatively breeding) of North American species of birds. Results failed to support the hypothesis of reduced long-distance dispersal among cooperative breeders. Thus, our results counter the conclusion that the lower rate of speciation among cooperative breeding taxa found in recent analyses is a consequence of reduced vagility.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000304151300006,

title = {An Experimental Study of Chick Provisioning in the Cooperatively  Breeding Acorn Woodpecker},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/koenig_walters2012ethology.pdf, PDF link},

doi = {10.1111/j.1439-0310.2012.02043.x},

issn = {0179-1613},

year  = {2012},

date = {2012-06-01},

urldate = {2012-06-01},

journal = {ETHOLOGY},

volume = {118},

number = {6},

pages = {566-574},

abstract = {Acorn woodpeckers (Melanerpes formicivorus) are cooperative breeders in which groups consist of a variable number of cobreeding males, joint-nesting females, and non-breeding helpers of both sexes that are offspring from prior nests. We temporarily manipulated brood size of nests to determine the feeding response of birds in relation to their status (breeder or non-breeding helper) and sex. All categories of birds responded similarly to brood size increases, adjusting their feeding rate upwards so as to maintain approximately the same per-nestling feeding rate. Breeders, however, exhibited more flexibility with respect to brood size reductions, decreasing their feeding rate while helpers did not. This suggests that the ‘feeding rules’ of helpers are less flexible than those of breeders, a result not previously detected in other cooperative breeders that have been studied to date. Particularly surprising was the finding that helpers maintain their feeding rates when brood demand is decreased rather than when it was increased, suggesting that the flexibility they exhibit is not a result of birds using the opportunity afforded by reduced brood demand to engage in other less cooperative activities.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000298386500022,

title = {Brooding, provisioning, and compensatory care in the cooperatively  breeding acorn woodpecker},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/koenig_walters2011behavecol.pdf, PDF link},

doi = {10.1093/beheco/arr172},

issn = {1045-2249},

year  = {2012},

date = {2012-01-01},

urldate = {2012-01-01},

journal = {BEHAVIORAL ECOLOGY},

volume = {23},

number = {1},

pages = {181-190},

abstract = {We analyzed reproductive investment in parental care (brooding and the provisioning of nestlings) in the acorn woodpecker (Melanerpes formicivorus), a cooperatively breeding species in which both polygynandry and helping-at-the-nest are common. As predicted based on the strategies pursued by birds of different sex and status, breeders generally invested more in parental care than helpers, and breeder females invested more than breeder males. Contrary to expectations, however, the degree to which individuals reduced their effort with increasing group size (i.e., patterns of load lightening or compensatory care) did not match overall investment. Instead, as group size increased, there was no significant difference in compensation in either brooding or provisioning among the different categories of birds. Compensation, at least by breeders, was significantly lower during the first week of the nestling period than later on, supporting the hypothesis that compensatory reduction in care is less likely when brood reduction is more common and was not affected by the acorn crop, which had no significant effect on the incidence of brood reduction despite being important to overall reproductive success. Our results offer support for the hypothesis that levels of compensation are influenced by the relative importance of brood reduction. More theoretical work, however, will be needed in order to understand the basis for patterns of compensation among individuals of different sex and status.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000297120000004,

title = {Fitness consequences of within-brood dominance in the cooperatively  breeding acorn woodpecker},

author = {Walter D. Koenig and Eric L. Walters and Joey Haydock},

url = {https://www.ericlwalters.org/koenigetal2011bes.pdf, PDF link},

doi = {10.1007/s00265-011-1231-1},

issn = {0340-5443},

year  = {2011},

date = {2011-12-01},

urldate = {2011-12-01},

journal = {BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY},

volume = {65},

number = {12},

pages = {2229-2238},

abstract = {Social dominance confers potential advantages in terms of access to superior resources, habitats, and breeding opportunities. In the cooperatively breeding acorn woodpecker (Melanerpes formicivorus), within-brood dominance among juveniles is correlated with relative body size as nestlings. Capitalizing on this relationship, we investigated the fitness consequences of dominance by means of paired comparisons of broodmates. We found that (1) larger fledglings retained at least some of their size advantage as adults; (2) overwinter survival of larger, dominant fledglings was significantly greater than subordinates, but was not relatively greater when resources were poor than when they were good; (3) among birds surviving their first winter, there were no differences vis-à-vis dominance in terms of the proportion of birds acting as helpers or inheriting their natal territory. However, larger, dominant males were present in the study area longer than subordinates, suggesting that they either survived better or were more successful at gaining reproductive opportunities; (4) if only one male broodmate became a helper instead of dispersing, he was significantly more likely to be the smaller subordinate, consistent with the view that helping is a best-of-a-bad-job strategy; and (5) there were no significant differences in reproductive success among pairs of male broodmates that cobred together as adults, consistent with prior work failing to detect a phenotypic correlation of reproductive skew. Our results indicate that within-brood dominance relationships established as juveniles have significant effects on first-year survivorship and at least some aspects of adult fitness.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000293884700002,

title = {Age-related provisioning behaviour in the cooperatively breeding acorn  woodpecker: testing the skills and the pay-to-stay hypotheses},

author = {Walter D. Koenig and Eric L. Walters},

url = {https://www.ericlwalters.org/koenig_walters2011animbehav.pdf, PDF link},

doi = {10.1016/j.anbehav.2011.05.028},

issn = {0003-3472},

year  = {2011},

date = {2011-09-01},

urldate = {2011-09-01},

journal = {ANIMAL BEHAVIOUR},

volume = {82},

number = {3},

pages = {437-444},

abstract = {Helpers in cooperatively breeding acorn woodpeckers, Melanerpes formicivorus, gain indirect fitness benefits by provisioning related offspring, but may also gain direct fitness benefits by any of several mechanisms. We tested the ‘skills’ hypothesis, which proposes that provisioning behaviour provides helpers with experience that allows them to be more successful when they breed later in life, and the ‘pay-to-stay’ hypothesis, which proposes that provisioning behaviour by helpers is rewarded by dominant breeders, allowing helpers to remain in their natal group longer, thus reaping nepotistic benefits. We found that young helpers provisioned at relatively low rates, which in most cases increased with age, a necessary requirement of the skills hypothesis. Analyses of birds with known feeding histories, however, revealed that helper males that fed young at higher rates had no greater reproductive success later in life than less helpful helper males, contrary to the skills hypothesis. In accord with pay-to-stay, males that fed more as second-year helpers remained in their natal group as helpers significantly longer and were more likely to inherit than were male broodmates that fed less. An analysis controlling for the time that birds remained in their natal groups, however, failed to indicate that prior feeding history played a significant role in these differences, which are more likely to be a consequence of differences in dispersal behaviour. In acorn woodpeckers, as in other species of cooperative breeders in which helpers are close relatives, the primary benefits of provisioning behaviour are indirect via kin selection rather than direct via either the acquisition of skills or payment of rent.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000292917900003,

title = {Variable helper effects, ecological conditions, and the evolution of cooperative breeding in the acorn woodpecker},

author = {Walter D. Koenig and Eric L. Walters and Joseph Haydock},

url = {https://www.ericlwalters.org/koenigetal2011amnat.pdf, PDF link},

doi = {10.1086/660832},

issn = {0003-0147},

year  = {2011},

date = {2011-08-01},

urldate = {2011-08-01},

journal = {AMERICAN NATURALIST},

volume = {178},

number = {2},

pages = {145-158},

abstract = {The ecological conditions leading to delayed dispersal and helping behavior are generally thought to follow one of two contrasting scenarios: that conditions are stable and predictable, resulting in young being ecologically forced to remain as helpers (extrinsic constraints and the habitat saturation hypothesis), or that conditions are highly variable and unpredictable, leading to the need for helpers to raise young, at least when conditions are poor (intrinsic constraints and the hard life hypothesis). We investigated how variability in ecological conditions influences the degree to which helpers augment breeder fitness in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus), a species in which the acorn crop, territory quality, and prior breeding experience all vary in ways that have important effects on fitness. We found that the relationship between ecological conditions and the probability that birds would remain as helpers was variable but that helpers generally yielded greater fitness benefits when ecological conditions were favorable, rather than unfavorable, for breeding. These results affirm the importance of extrinsic constraints to delayed dispersal and cooperative breeding in this species, despite its dependence on a highly variable and unpredictable acorn crop. Our findings also confirm that helpers can have very different fitness effects, depending on conditions, but that those effects are not necessarily greater when breeding conditions are unfavorable.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000291754800011,

title = {Effects of gypsy moth outbreaks on North American woodpeckers},

author = {Walter D. Koenig and Eric L. Walters and Andrew M. Liebhold},

url = {https://www.ericlwalters.org/gypsymoth2011.pdf, PDF link},

doi = {10.1525/cond.2011.100039},

issn = {0010-5422},

year  = {2011},

date = {2011-05-01},

urldate = {2011-05-01},

journal = {CONDOR},

volume = {113},

number = {2},

pages = {352-361},

abstract = {We examined the effects of the introduced gypsy moth (Lymantria dispar) on seven species of North American woodpeckers by matching spatially explicit data on gypsy moth outbreaks with data on breeding and wintering populations. In general, we detected modest effects during outbreaks: during the breeding season one species, the Red-headed Woodpecker (Melanerpes erythrocephalus), increased over pre-outbreak levels, while during the winter one species, the Yellow-bellied Sapsucker (Sphyrapicus varius), increased and one, the Downy Woodpecker (Picoides pubescens), decreased from pre-outbreak levels. Responses following outbreaks were similarly variable, and in general we were unsuccessful at predicting population responses to outbreaks from a priori knowledge of woodpecker ecology and behavior. We did, however, find evidence that the response of at least half of the species changed over the 34-year period covered by the study: except for the Northern Flicker (Colaptes auratus), whose response to outbreaks during the winter decreased, populations generally responded more positively to outbreaks with time. This temporal response suggests that North American woodpeckers may be taking greater advantage of the resource pulse and/or habitat changes caused by outbreaks of this exotic pest now than previously, so in the future the effects of gypsy moth outbreaks on these species may increase.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000284172800016,

title = {Quantifying purported competition with individual- and population-level metrics},

author = {Eric L. Walters and Frances C. James},

url = {https://www.ericlwalters.org/walters_james2010.pdf, PDF link},

doi = {10.1111/j.1523-1739.2010.01516.x},

issn = {0888-8892},

year  = {2010},

date = {2010-12-01},

urldate = {2010-12-01},

journal = {CONSERVATION BIOLOGY},

volume = {24},

number = {6},

pages = {1569-1577},

abstract = {Competitive species interactions may contribute to population declines. Purportedly, Red-bellied Woodpeckers (Melanerpes carolinus), a common species, and Red-cockaded Woodpeckers (Picoides borealis), an endangered species, compete for roosting and nesting cavities in living pine trees. To determine whether behavioral interactions measured at the individual level manifest themselves at the population level, we conducted field experiments designed to test whether the presence of Red-bellied Woodpeckers resulted in a decrease in fitness to Red-cockaded Woodpeckers. As part of a 4-year study examining the nature of interspecific interactions in two populations of Red-cockaded Woodpeckers (one stable, the Apalachicola Ranger District; one declining, the Wakulla Ranger District) in the Apalachicola National Forest, Florida, we conducted a set of Red-bellied Woodpecker removal experiments. Paradoxically, following the removal of Red-bellied Woodpeckers, we observed decreases in Red-cockaded Woodpecker group size, proportion of nests that were successful, and proportion of individuals remaining on territories. Removal of Red-bellied Woodpeckers may have exaggerated the immigration rate of Red-bellied Woodpeckers to Red-cockaded Woodpecker territories. The Red-cockaded Woodpeckers in the Apalachicola Ranger District likely can withstand pressure from immigrating Red-bellied Woodpeckers given that their population has remained relatively stable despite the presence of Red-bellied Woodpeckers. A major factor of population persistence in the Wakulla Ranger District was the high turnover rate of adult female Red-cockaded Woodpeckers, a phenomenon that was exacerbated by removal of Red-bellied Woodpeckers. Relying solely on observations of apparently competitive interactions between individuals may not necessarily provide information about population-level outcomes. Paradoxically, removing species that appear to be competitors may harm species of concern.},

keywords = {cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000269112000011,

title = {Helpers and egg investment in the cooperatively breeding acorn  woodpecker: testing the concealed helper effects hypothesis},

author = {Walter D. Koenig and Eric L. Walters and Joseph Haydock},

url = {https://www.ericlwalters.org/koenig_etal_2009.pdf, PDF link},

doi = {10.1007/s00265-009-0773-y},

issn = {0340-5443},

year  = {2009},

date = {2009-09-01},

urldate = {2009-09-01},

journal = {BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY},

volume = {63},

number = {11},

pages = {1659-1665},

abstract = {In cooperatively breeding acorn woodpeckers (Melanerpes formicivorus), helper males have a large positive effect on fledging success in good acorn crop years but only a small positive effect in poor acorn crop years, while helper females exhibit the opposite pattern. Based on these findings, we tested the “concealed helper effects” hypothesis, which proposes that laying females reduce investment in eggs (with respect to their size, number, or quality) in a way that confounds helper effects and results in an absence of a relationship between helpers and breeding success. Results generally failed to support the hypothesis. Mean egg size was positively related to temperatures during the 10 days prior to egg-laying and negatively related to the food supply as indexed by the prior fall’s acorn crop, but there were no significant differences vis-à-vis helpers except for interactions with the acorn crop that only partly corresponded to those predicted. With respect to clutch size, females laid larger clutches when assisted by female helpers, opposite the pattern predicted. Although our results suggest that egg size is adjusted to particular ecological circumstances, we conclude that neither egg nor clutch size is adjusted in a way that confounds the apparent effects of helpers, as proposed by the concealed helper effects hypothesis.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000260229000003,

title = {Acorn harvesting by acorn woodpeckers: annual variation and comparison  with genetic estimates},

author = {Walter D. Koenig and Jay P. McEntee and Eric L. Walters},

url = {https://www.ericlwalters.org/koenigetal2008.pdf, PDF link},

issn = {1522-0613},

year  = {2008},

date = {2008-10-01},

urldate = {2008-10-01},

journal = {EVOLUTIONARY ECOLOGY RESEARCH},

volume = {10},

number = {6},

pages = {811-822},

abstract = {Questions: (1) How does the effort that birds invest in harvesting acorns, including the distance the acorns are moved – a key factor affecting population structure of the trees – covary with the size of the acorn crop? (2) How well are harvest patterns, previously inferred by indirect, genetic methods, matched by data from direct observations of harvesting?

Organisms: The acorn woodpecker (Melanerpes formicivorus), a cooperatively breeding species that is highly dependent on acorns, which are stored in specialized storage trees known as granaries.

Methods: We observed acorn harvesting over 4 years at Hastings Reservation in central coastal California, a period over which acorn crops varied considerably in size. 

Results: Birds harvested 94% of acorns from a small number of trees located within 150 m of

their granary. The distances travelled by birds to harvest acorns and the number of trees from

which acorns were harvested were both greater in a poor acorn year than when the crop was

good. Birds did not necessarily prefer the species of acorn that was most abundant. The

distance birds travelled to harvest acorns, harvesting overlap among groups, and the number of

trees from which acorns were harvested generally matched the findings of Grivet et al. (2005),

indicating that an indirect genetic approach can be effective when direct observation of seed

dispersal is difficult.},

keywords = {acorn woodpecker, cooperative breeding, peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000233390700008,

title = {Seasonal body weight variation in five species of woodpeckers},

author = {WD Koenig and EL Walters and JR Walters and JS Kellam and KG Michalek and MS Schrader},

url = {https://www.ericlwalters.org/koenigetal2005.pdf, PDF link},

doi = {10.1650/7718.1},

year  = {2005},

date = {2005-11-01},

urldate = {2005-11-01},

journal = {CONDOR},

volume = {107},

number = {4},

pages = {810-822},

abstract = {We investigated patterns of seasonal variation in body weight in six populations of five resident species of temperate-zone woodpeckers: Acorn Woodpecker (Melanerpes formicivorus), Red-bellied Woodpecker (M. carolinus), Red-cockaded Woodpecker (Picoides borealis), Downy Woodpecker (P. pubescens), and Great Spotted Woodpecker (Dendrocopos major). After controlling for time of day and overall body size, annual variation in body weight was small and generally not statistically significant. However, analysis revealed evidence of significant “winter fattening,” comparable in magnitude to other temperate-zone resident species, in three of the species. The degree of winter fattening did not correlate with either the size of the acorn crop (for the Acorn Woodpecker) or latitude, two variables potentially related to predictability of food resources. However, the smaller species exhibited significantly greater winter fattening than the larger species, as predicted by the hypothesis that energy storage should be more important for small-bodied species. Furthermore, the food-storing Acorn Woodpecker exhibited considerably less winter fattening than the nonfood-storing species, supporting the hypothesis that food storage provides an ecological alternative to winter fattening.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000227072800008,

title = {Knock on wood: woodpeckers and utility pole damage},

author = {RE Harness and EL Walters},

url = {https://www.ericlwalters.org/harnesswalters2005.pdf, PDF link},

doi = {10.1109/MIA.2005.1405829},

issn = {1077-2618},

year  = {2005},

date = {2005-03-01},

urldate = {2005-03-01},

journal = {IEEE INDUSTRY APPLICATIONS MAGAZINE},

volume = {11},

number = {2},

pages = {68-73},

abstract = {This work discusses how protect pole damages form woodpeckers. Wire mesh is the most widely used barrier to prevent damage. When selecting a barrier, it is critical to know which woodpecker species are causing pole damage. The most commonly used mesh is 19-gauge galvanized wire in a 1/4-in mesh pattern. Larger species, such as the pileated woodpecker, can penetrate 19-gauge wire, so a heavier gauge wire is required. It is becoming common for utilities to repair woodpecker cavities in wood poles with fillers in an effort to extend the pole's useful life. There are a variety of tools to calculate damage and determine if a pole can be repaired or must be replaced. A number of repair products are discussed.},

keywords = {peer-reviewed, utility structure-woodpecker, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000181700500013,

title = {Seasonal prevalence of a haematozoan parasite of red-bellied woodpeckers  (Melanerpes carolinus) and its association with host condition and  overwinter survival},

author = {MS Schrader and EL Walters and FC James and EC Greiner},

url = {https://www.ericlwalters.org/schrader_etal_2003.pdf, PDF link},

doi = {https://doi.org/10.1093/auk/120.1.130},

year  = {2003},

date = {2003-01-01},

urldate = {2003-01-01},

journal = {AUK},

volume = {120},

number = {1},

pages = {130-137},

abstract = {We examined seasonal prevalence of a haematozoan parasite (Haemoproteus velans) of the Red-bellied Woodpecker (Melanerpes carolinus) in the Apalachicola National Forest, northern Florida. We also investigated how infection with H. velans was associated with host mass, body condition, and overwinter survival. Analysis of blood smears taken from individual woodpeckers between May 2000 and July 2001 indicated that prevalence of H. velans peaked in July 2000, at ∼80% of individuals sampled, decreased to 0% in January and February 2001, and peaked again in July 2001, at ∼50% of individuals. Infection with H. velans was associated with low mass and poor body condition in males. Infection showed no association with female mass. In addition, infection with H. velans showed no relationship with overwinter survival. Our data reemphasize the importance of considering seasonal variation in parasite prevalence during testing for haematozoa. In addition, our data suggest that, although infection with H. velans is associated with poorer host condition, it does not negatively affect host survival.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000180255000015,

title = {Parasitic helminths of red-bellied woodpeckers (Melanerpes carolinus)  from the Apalachicola National Forest in Florida},

author = {GW Foster and JM Kinsella and EL Walters and MS Schrader and DJ Forrester},

url = {https://www.ericlwalters.org/foster_et_al2002.pdf, PDF link},

doi = {10.1645/0022-3395(2002)088[1140:PHORBW]2.0.CO;2},

issn = {0022-3395},

year  = {2002},

date = {2002-12-01},

urldate = {2002-12-01},

journal = {JOURNAL OF PARASITOLOGY},

volume = {88},

number = {6},

pages = {1140-1142},

abstract = {Seventy-four red-bellied woodpeckers (Melanerpes carolinus) from the Apalachicola National Forest (30°10′N, 84°40′W) in northwest Florida were examined for helminths. The most prevalent parasites were the nematode Aproctella stoddardi (11%) and the acanthocephalan Mediorhynchus centurorum (11%). New host records include Pseudaprocta samueli, A. stoddardi, Tridentocapillaria tridens, Diplotriaena americana, Dispharynx nasuta, Procyrnea pileata, Orthoskrjabinia rostellata, and Brachylaima fuscatum. The helminth fauna was characterized by low prevalences and intensities of infection and low numbers of species per bird (1.2). The frequency of prescribed burning and habitat understory flora composition did not influence the prevalences or intensities of helminths in red-bellied woodpeckers collected from 2 similar but differently managed sites within the forest.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000175520500004,

title = {Predation on nesting woodpeckers in British Columbia},

author = {EL Walters and EH Miller},

url = {https://www.ericlwalters.org/waltersmiller2001.pdf, PDF link},

issn = {0008-3550},

year  = {2001},

date = {2001-07-01},

urldate = {2001-07-01},

journal = {CANADIAN FIELD-NATURALIST},

volume = {115},

number = {3},

pages = {413-419},

abstract = {Predation on eggs, nestlings, and breeding adults of Red-naped Sapsuckers, Sphyrapicus nuchalis, Northern Flickers, Colaptes auratus, Hairy Woodpeckers, Picoides villosus, and Williamson's Sapsuckers, S. thyroideus, was documented in the Hat Creek valley, south-central British Columbia from 1989-1994. Predation by Black Bears (Ursus americanus), Deer Mice (Peromyscus maniculatus), and House Wrens (Troglodytes aedon) was observed; and predation by Long-tailed Weasels (Mustela frenata) was inferred.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000078730200010,

title = {Plumage, size, and sexual dimorphism in the Queen Charlotte Islands Hairy Woodpecker},

author = {EH Miller and EL Walters and H Ouellet},

url = {https://www.ericlwalters.org/milleretal.pdf, PDF link},

doi = {10.2307/1370449},

issn = {0010-5422},

year  = {1999},

date = {1999-02-01},

urldate = {1999-02-01},

journal = {CONDOR},

volume = {101},

number = {1},

pages = {86-95},

abstract = {Plumage, size, and sexual dimorphism of the endemic Hairy Woodpecker subspecies Picoides villosus picoideus are described and compared with a less isolated insular population. Museum specimens of P. v. picoideus from the Queen Charlotte Islands, British Columbia were compared with P. v. harrisi specimens from Vancouver Island, British Columbia. Specimens from the two localities are similar in size, although the culmen of P. v. picoideus is 5-6% shorter. In plumage, P. v. picoideus is distinct in having markings on the belly and flanks, dorsal barring, and barring on the outer rectrices. The breast and belly are much darker and the wing coverts have fewer white markings in P. v. picoideus than in P. v. harrisi. Adults and juveniles, and adult males and females, differ only in minor features of plumage. Adult plumage of P. v. picoideus and insular populations of P. villosus in Newfoundland and the Grand Bahamas resembles juvenal plumage in mainland locations, and includes ancestral traits in this woodpecker lineage. Sexual dimorphism in size is similar in P. v. picoideus, P. v. harrisi, and continental populations, suggesting no ecological release of the sexes on the Queen Charlotte Islands or Vancouver Island. Relative sexual dimorphism in bill size varies little over the species' range, hence appears to be influenced little by ecological factors.},

keywords = {peer-reviewed, woodpecker},

pubstate = {published},

tppubtype = {article}

}