Research
My research program
encompasses facets of community ecology,
theoretical ecology, conservation biology, and evolution. I
use a variety of scientific approaches to integrate applied,
theoretical, and basic research. Methods of investigation
include field experiments, long-term
demographic studies, and mathematical modeling in order to
understand how species
interact with each other and their environment; all within a
larger conservation biology framework. For ease of
presentation, I have tried to pigeon-hole my research into the
following broad categories. Please realize, however, that
there is much overlap among the categories that I provide
below.
Evolution of Mating
Systems
Ecological
Constraints in the Cooperatively Breeding Acorn Woodpecker
Collaborators: Walter D.
Koenig (Cornell University); Joey Haydock (Gonzaga University)
ONGOING RESEARCH
 The mating
system of the acorn woodpecker (Melanerpes formicivorus) is among the
most complex of any vertebrate, with groups consisting of a breeding core of
up to seven cobreeding males and three joint-nesting females mating together
(cooperative polyyamy or polygynandry) in combination with a variable number
of nonbreeding helpers that are offspring from prior years and that have
delayed dispersal to remain on their natal territory. Cobreeders of the same
sex are almost always close relatives, either siblings or parents and
offspring. The project tests experimentally the role of roosting and
nesting cavities and of storage facilities in which groups store acorns as
ecological constraints leading to delayed dispersal by offspring and
cooperative polygamy by same-sex coalitions of relatives. The project involves a thorough survey of cavities and storage facilities of existing
groups and an experiment in which artificial cavities and storage facilities
were provided in previously unused areas. The incidence and rate of
colonization of experimental sites compared to control sites, together with
the origin and identity of colonists, are being used to accept or reject these
hypotheses. The project will provide new insights into the role of
ecological constraints to the evolution of cooperative breeding, including
not only delayed dispersal and helping at the nest but also cooperative
polygamy. The project focuses specifically on the interactions between
ecological constraints, social factors such as group size and composition,
and variation in territory quality as factors influencing these social
phenomena. The study involves work in California oak woodland, a threatened
habitat known for its biodiversity, and continues a long-term project that
contributes to our knowledge of how ecosystems are affected by human-induced
changes.
Walters, E.L., J.
Haydock, and W.D. Koenig. Dispersal of
breeders in the acorn woodpecker: why leave if you can breed?
Submitted / In Revision.
Koenig, W.D., J.P.
McEntee, and E.L. Walters. 2008. Acorn harvesting by acorn woodpeckers:
annual variation and comparison with genetic estimates.
Evolutionary Ecology Research 10:811-822. Koenig,
W.D., E.L. Walters, and J. Haydock. 2009. Helpers and egg size in the
cooperatively breeding acorn woodpecker: testing the concealed
helper effects hypothesis. Behavioral Ecology
& Sociobiology 63:1659-1665.
We hire field assistants year
round. If interested, see
our employment
page.
Community Ecology
Markov Properties of Species Assemblages
Collaborators: Matthew Spencer (University
of Liverpool)
ONGOING RESEARCH
 The
succession of species assemblages has been modeled as a
Markovian process by investigators for over 40 years. We are
challenging some of the assumptions and generalizations that
have been used over the past four decades. Inherent problems are
illustrated through our analysis of various datasets and a
meta-analysis of published studies.
Trophic
Cascades in Fragmented Coastal Sage Scrub Habitat
Collaborators: Douglas T.
Bolger (Dartmouth College); Jay Diffendorfer (Illinois Natural
History Survey); Michael Anguiano (San Diego State University);
Michael Patten (University of Oklahoma)
ONGOING RESEARCH
Food web theory provides a useful framework
for management of ecosystems, and complements
well the more traditional population-level approach. However,
the applicability of food web concepts, including keystone species
and top-down cascades, to ecosystems of conservation concern
is unclear. Our project examines changes in predator-prey interactions
in the coastal sage scrub ecosystem of southern California caused
by habitat fragmentation, associated with urban development.
This project focuses on four landscape treatments in coastal
San Diego County that vary in the degree of exposure to urban
edge and fragmentation: interior of large habitat blocks (>1000ha),
 urbanized
edge of large blocks, large habitat fragments (50-100 ha) and
small fragments (5-20 ha). This research expands previous work
by continuing demographic studies on birds; but with simultaneous
estimation of mesocarnivore, snake, and raptor abundance and
activity to estimate their effects and to examine how these
vary with habitat fragmentation. The work will determine if
nest predation, juvenile and adult bird survival, as well as
small mammal abundance and survival vary with fragment size
and predator composition. In addition, it investigates the role
of snakes and raptors and determines their effect relative to
mammalian predators by comparisons across experimental treatments
and by path analysis. By comparing bird responses to small mammals,
this project addresses the question of whether all primary consumers
are vulnerable to cascades, or if the biological differences
between taxa make one group more susceptible to top-down regulation
than another.
Our research findings were recently featured. See Warren et al.
2006.
Urban food webs: predators, prey, and the people who feed them.
Ecological Bulletin 87(4):387-393. Walters,
E.L, D.T. Bolger, and M.A. Patten. No effect of urban
fragmentation on reproduction in coastal sage scrub avifauna.
Submitted / In Revision. Hellmuth,
S.M., E.L. Walters, and D.T. Bolger. A
comparison of the effects of temperature on the diel and seasonal
nestling provisioning patterns of the California Towhee and the
Wrentit. Submitted / In Revision. 2004
Field Crew Photo
2005
Field Crew Photo
2006
Field Crew Photo
Estimating
species interactions in a woodpecker tree-hole community at
the individual, population, and community levels
Collaborator: Frances C.
James (Florida State University)
ONGOING RESEARCH
 Species
assemblages are often dependent upon a discrete resource (e.g.
dung patches, pitcher plants, and carcasses).
Often, these types of discrete resources are ephemeral or temporary
in nature. Through both empirical (field experiments in the
Apalachicola National Forest) and theoretical (modeling) work,
I examine the nature in which these dynamic resources determine
the species assemblage associated with them.
The system that I work with is the community associated with
Red-cockaded Woodpecker cavities. The cavities are excavated
by Red-cockaded Woodpeckers and then used by a variety of mammals,
birds, reptiles, amphibians, and invertebrates. Most of the
occupants (birds and mammals) use the cavities for reproduction
and, thus, the cavity is integral to their life history. I have
examined the properties of the cavities such as the rate at
which they are recruited and lost from the system and the rate
at which they change in size over time. Species interactions
that occur among members of the community were determined empirically
through a variety of experiments that manipulated both cavities
and species within the community. Some of the publications that
have emerged (and will emerge) from this work are outlined below.
Walters, E.L.
and F.C. James. Short-term dynamics among species using a discrete
resource, cavities in living pines. Submitted / In Revision.
Walters, E.L..
Using Markov chain community development models within a
conservation framework. Submitted / In Revision.
Walters, E.L.
and F.C. James. 2010. Quantifying
purported competition with individual- and population-level
metrics. Conservation Biology. In Press.
Resource
Ratio Theory
Collaborators: Thomas E.
Miller (Florida State University); Jean H. Burns (Washington
University); Hannah L. Buckley (Lincoln University); Jamie M.
Kneitel (Cal State, Sacramento); Nicolas Mouquet (University of
Montpelier); Pablo Munguia (Smithsonian Environmental Research
Center); Paul M. Richards (NOAA)
A
model of species interactions based on their use of shared
resources was proposed in 1972 by Robert MacArthur and later
expanded by David Tilman. This "resource-ratio theory" has been
used to make a number of testable predictions about competition
and community patterns. We reviewed 1,333 papers that cite
Tilman’s original two publications to determine whether
predictions of the resource-ratio theory have been adequately
tested and to summarize their general conclusions. Most of the
citations do not directly test the theory: only 26 studies
provide well-designed tests of one or more predictions,
resulting in 42 individual tests of predictions. Most of these
tests were conducted in the laboratory or experimental
microcosms and used primary producers in freshwater systems. You
can read more about our findings in the following publications.
Miller, T.E.,
J.H. Burns, P. Munguia, E.L. Walters, J.M. Kneitel, P.M. Richards,
N. Mouquet, and H.L. Buckley. 2005.
A critical review of twenty years'
use of the Resource Ratio Theory. American Naturalist
165(4):439-448.
Miller, T.E.,
J.H. Burns, P. Munguia, E.L. Walters, J.M. Kneitel, P.M. Richards,
N. Mouquet, and H.L. Buckley. 2007.
Evaluating support for the
resource-ratio hypothesis: a response to Wilson et al. American Naturalist 169(5):707-708.
Phytotelmata
Container
habitats provide ideal opportunities for the study of community
ecology. Each container provides the habitat for an entire
community of organisms. We studied organisms associated with two
types of phyotelmata: pitcher plants and woodpecker tree holes
of northern Florida.
Pitcher
Plants
 2004.
Buckley, H., J. Burns, J. Kneitel, E.L. Walters, P. Munguia,
and T.E. Miller. Small-scale patterns
in community structure of Sarracenia purpurea inquilines.
Community Ecology 5(2):181-188.
Water-filled Woodpecker Tree Holes
Walters, E.L.
and J.M. Kneitel. 2004. Use of water-filled red-cockaded woodpecker
cavities by other organisms. Pp. 492-497 in: Costa, R. and S.J. Daniels,
eds. Red-cockaded woodpecker: road to recovery. Hancock House
Publishers, Blaine, Washington.
CONSERVATION BIOLOGY
Red-cockaded Woodpecker Habitat Structure
Collaborators:
Frances C. James (Florida State University); Charles A. Hess (US
Forest Service)
ONGOING RESEARCH
 Since
early 1997 I have been heavily involved in Red-cockaded
Woodpecker (an endangered species) management activities. As
part of our research group at Florida State University, we have
been examining the effect of fire, forestry activity,
competitors, and the U.S. Fish & Wildlife Service's
translocation program on the largest remaining population
(approximately 600 groups in the Apalachicola National Forest)
of Red-cockaded Woodpeckers in the world. The following chapter
examines forest structure and contrasts two populations of
red-cockaded woodpeckers with respect to the size distribution
of pine trees. We are currently examining other demographic
differences between the two populations with 15 years of
demographic data.
James, F.C.,
Richards, P., Walters, E.L., Schrader, M., Hess, C.A. and K.
McCluney. 2004. Sustainable forestry for the red-cockaded woodpecker’s
ecosystem. Pp. 60-69 in: Costa, R. and S.J. Daniels, eds. Red-cockaded
woodpecker: road to recovery. Hancock House Publishers, Blaine,
Washington.
Red-headed
Woodpecker Population Declines
Red-headed
woodpeckers have undergone large population declines over much
of their range. We examine various potential causes and make
recommendations on how to reverse the population decline.
Koenig, W.D.
and E.L. Walters. Submitted. Testing alternative hypotheses for
the cause of population declines: the case of the Red-headed
Woodpecker.
Habitat
Conservation Plans
/ Species Management Plans
I was part of
an NCEAS (National Center for Ecological Synthesis and Analysis)
working group examining the science behind the United States
Fish & Wildlife Service's Habitat Conservation Plan. Under
Section 10 of the Endangered Species Act, Habitat Conservation
Plans must be developed when endangered species are found on
private land and a risk of "take" is apparent. We
summarized the science behind all of the HCPs that had been
conducted up until the date we initiated our analysis. The fruit
of our labor was published in Conservation Biology in 2001.
Prior to this work, I had coauthored species management plants
for the red and blue listed forest and grassland birds of
British Columbia.
 Harding,
E.K., E.E. Crone, B.D. Elderd, J.M. Hoekstra, A.J. McKerrow,
J.D. Perrine, J. Regetz, L.J. Rissler, A.G. Stanley, E.L. Walters*,
and NCEAS HCP Working Group. 2001. The
scientific foundations of habitat conservation plans: a quantitative
assessment. Conservation Biology 15:488-500 (*order of authors
alphabetical after lead author)
Fraser, D.F.
and E. Walters. 1993. Preliminary species management plan for
Brewer’s Sparrow, subspecies breweri, in British
Columbia. British Columbia Ministry of Environment, Lands and
Parks Report, Victoria. 12pp.
Fraser, D.F.,
E.L. Walters, and C. Siddle. 1990. Species management plans
for the red and blue listed forest and grassland birds of British
Columbia. Contract report to the Wildlife Branch, Ministry of
Environment, Victoria, B.C.
Transportation-related
Wildlife Mortality
Collaborator:
Matthew J. Aresco (Nokuse Plantation)
ONGOING RESEARCH
I have been
interested in the effect of roads on population demographics for
a number of years. As a former member of the Lake Jackson Ecopassage Advisory Group,
we were charged with making recommendations on how to stem the unprecedented wildlife mortality associated
with US Highway 27 at Lake Jackson, Florida. This 1-km stretch
of highway has the highest turtle road mortality ever recorded
worldwide. For more information, see the Lake
Jackson Ecopassage web site that has been set up. A
similar situation is occurring with the
endangered Alabama
Red-bellied Turtle. We are currently working on some
demographic models that show the population is currently headed
to extinction, given yearly mortality attributed to roads.
Purple
Martin Population Declines
In the early
1990s, I was part of a study that documented that fewer than 30
Purple Martins were left in British Columbia. We erected
hundreds of nest boxes in a last-ditch conservation effort to
prevent the species from being extirpated from the province. It
worked - recent population estimates are currently in the
hundreds.
Fraser, D.F.,
C. Siddle, D. Copley and E. Walters. 1997. Status
of the Purple Martin in British Columbia. Wildlife Working
Report No. WR-89. 38 p.
Copley, D.R.
and E.L. Walters. 1991. Purple Martin nest box programme summary
- 1990. Victoria Naturalist 47:4-9.
Siddle, C., E.L.
Walters, and D.R. Copley. 1991. Status report of the Purple
Martin, Progne subis, in British Columbia. Contract
report to the Wildlife Branch, Ministry of Environment, Victoria,
B.C.
Walters, E.L.,
D.R. Copley and S.J. Statton. 1990. Purple Martin report finds
fewer than 30 birds left in B.C. Victoria Naturalist 47:1-4.
Utility
Structure - Wildlife Interactions
Collaborator:
Richard E. Harness (EDM International, Inc.)
 Since
1997 I have been working with utility organizations and companies
throughout the United States and Canada to examine factors influencing
wildlife - utility structure interactions. The focus of my work
has been on determining the extent to which woodpeckers damage
utility structures and evaluating potential preventative and
mitigative measures. My research has found that most woodpeckers
are using wood utility structures for either nesting or foraging
activities. Ways of preventing such damage depend upon the species
involved, geographic location, nearby habitat structure, integrity
of the pole, chemical treatment of the pole, previous mitigation
measures, and many other factors. Each case of damage must be
examined on an individual basis - there are no general trends
that allow companies to predict utility structure susceptibility
to damage. A field visit (supplemented with historical information)
is usually necessary so that recommendations can be made to
prevent, reduce, or repair woodpecker damage.
Harness, R.E.
and E.L. Walters. 2005. Knock on wood: woodpeckers and utility pole damage. IEEE Industry Applications Magazine
11(2):68-73.
2004. Harness, R.E. and
E.L. Walters.
Woodpeckers and utility pole
damage. Rural Electric Power Conference. May 23-25, 2004,
Scottsdale, AZ. 7p.
Harness, R.E.
and E.L. Walters. 2003. Mitigating woodpecker damage to utility
poles. Western Energy Institute and Northwest Public Power Association.
November 5-6, 2003, Reno, NV. 11p.
Walters, E.L.
2001. When good woodpeckers go bad: why do they damage utility
structures? Western Energy Institute and Northwest Public Power
Association. October 2001, Reno, NV. 6p.
Walters, E.L.
2000. Woodpeckers 101: the basics of woodpecker biology. Northeast
Pole Conference. October 2000, Binghamton, NY. 7p.
Walters, E.L.
1997. Woodpecker biology and behavior. Electric Power Research
Institute. May 1997, Charlotte, NC. 6p.
Marine
Mammals
Baird, R.W.,
Walters, E.L. and P.J. Stacey. 1993.
Status of the Bottlenose Dolphin,
Tursiops truncatus, in Canada. Canadian Field-Naturalist
107(4):466-480. Reprints available
upon request
Walters, E.L.
R.W. Baird and T.J. Guenther. 1992.
New killer whale “pod” discovered
near Victoria. Victoria Naturalist 49(3):7-8.
WILDLIFE BIOLOGY
Cavity-nesting Birds
I have been
studying cavity-nesting birds
(47 species) and mammals since 1990. To date, I
have had the opportunity to report on and/or conduct research on
19 of the 22
species of woodpeckers found in North America.
Field work has been conducted at research sites
in Arizona, British Columbia, California, and Florida. The bulk
of my postgraduate thesis and dissertation work has examined
hole-nesting communities associated with woodpecker holes.
Habitat
and space use of the Red-naped Sapsucker, Sphyrapicus nuchalis,
in the Hat Creek Valley, south-central British Columbia
Collaborator: Edward H. Miller (Memorial University)
ONGOING RESEARCH
 Red-naped
Sapsuckers are purported to be keystone species in the communities
in which they are found. My MS research examined the nature
in which sapsuckers use habitat and space. Using radio telemetry,
I established home range estimates and documented their use
of habitat as they foraged and nested. This study was part of
a larger study initiated by my former advisor, Ted Miller, in
1989. Some of the publications that have resulted from this
work are listed below.
Walters, E.L.
1996. Habitat and space use of
the Red-naped Sapsucker, Sphyrapicus nuchalis, in the
Hat Creek Valley, south-central British Columbia. MSc. Thesis,
University of Victoria, Victoria, B.C. Canada. Erratum
 Walters,
E.L. and E.H. Miller. 2001. Predation
on woodpeckers in British Columbia. Canadian Field-Naturalist
115(3): 413-419. Reprints available
upon request
Walters, E.L.,
E.H. Miller, and P.E. Lowther. 2002. Red-breasted Sapsucker
(Sphyrapicus ruber) and Red-naped Sapsucker (Sphyrapicus
nuchalis). In The Birds of North America, No. 663 (A. Poole
& F. Gill, Eds.). The Birds of North America, Inc., Philadelphia,
PA. Reprints available upon request
Walters, E.L.,
E.H. Miller, and P.E. Lowther. 2002. Yellow-bellied
Sapsucker (Sphyrapicus varius). In The Birds of
North America, No. 662 (A. Poole & F. Gill, Eds.). The Birds
of North America, Inc., Philadelphia, PA. Reprints
available upon request
Walters,
E.L.
2004. Study
identifies nest-cavity predators: woodpecker nests in British
Columbia are examined. Bluebird 26:15-17.
Walters, E.L.
and E.H. Miller. Factors affecting nest success in Red-naped
Sapsuckers. Submitted / In Revision.
Walters, E.L.
Revision of Birds of North America accounts: Red-breasted
Sapsucker and Red-naped Sapsucker. In Progress. Expected
Completion: Sep. 15, 2008.
Miscellaneous Research on Woodpeckers
Koenig, W.D., E.L. Walters, J.R. Walters, J.S. Kellam, K.G. Michalek,
and M.S. Schrader. 2005. Seasonal body weight variation in five
species of woodpeckers. Condor 107(4):810-822.
Miller, E.H.,
E.L. Walters and H. Ouellet. 1999. Plumage,
size, and sexual dimorphism in the Queen Charlotte Islands Hairy
Woodpecker. Condor 101:86-95.
Steeger, C.,
M. Machmer and E. Walters. 1996. Ecology and management of woodpeckers
and wildlife trees in British Columbia. Fraser River Action
Plan, Environment Canada, Ottawa. 23p. Reprints
available upon request
Walters, E.L.
1994. A critical review of “A methodology for surveying
woodpeckers in British Columbia”. Contract report to the
Wildlife Branch, Ministry of Environment, Victoria, B.C.
Radio
Telemetry
I have been
conducting telemetric studies for over 14 years, beginning with my postgraduate
work on space use by
Red-naped Sapsuckers in 1994. This was followed a year later
with
telemetry work in Arizona involving Red-naped Sapsuckers,
Williamson's Sapsuckers, Red-breasted Nuthatches, Pygmy
Nuthatches, Hermit Thrushes, and Orange-crowned Warblers. Other
projects later on included research on Red-bellied Woodpeckers in Florida
(1997) and
California Towhees (2004-2006). In 1996 I helped
coauthor a standards manual that is used by the British Columbia
government for anyone initiating
telemetry studies in that province.
Andrusiak, L,
E.L. Walters, T. Eliot and K. Simpsons. 1996. Standards
manual for wildlife radio telemetry. Resources Inventory
Committee, Ministry of Environment, Lands, and Parks, Victoria,
B.C.
Wildlife Viewing Plans
 Walters, E.L.
and D.R. Copley. 1991. Waterfowl use of the Martindale Flats
management area. Report to the Parks & Conservation Committee,
Victoria Natural History Society. Victoria, B.C.
Fraser,
D.F., C. Berryman, E.L. Walters and L.R. Ramsay. 1990. Wildlife
viewing plan for Goldstream Provincial Park. Contract report
to the Ministry of Parks, Vancouver, B.C.
Fraser, D.F.,
L.R. Ramsay, and E.L. Walters. 1990. Wildlife viewing plan for
Manning Provincial Park. Contract report to the Ministry of
Parks, Vancouver, B.C.
Wildlife
Diseases / Parasites
Wildlife diseases and
parasites play important roles in regulating populations. In the
publications listed below, we show that mortality due to a
protozoan accounted for mortality estimates upwards of 100,000
Band-tailed Pigeons in a 2-month period. Work with haematozoan
parasites of Red-bellied Woodpecker revealed that only males
exhibited decreased mass and body condition with parasite loads.
Stromberg, M.R.,
W.D. Koenig, E.L. Walters, and J. Schweisinger.
2008. Estimate of Trichomonas gallinae-induced
mortality in band-tailed pigeons, upper Carmel Valley,
California, winter 2006-2007. Wilson Journal of Ornithology
120(3):603-606.
 Schrader, M.S.,
E.L. Walters, F.C. James., and E.C. Greiner. 2003. Seasonal
prevalence of a haematozoan parasite of the Red-bellied Woodpecker
(Melanerpes carolinus) and its association with host
condition and overwinter survival. AUK 120(1):130-137.
Foster,
G.W., J.M. Kinsella, E.L. Walters, M.S. Schrader, and D.J. Forrester.
2002. Parasitic helminths of
red-bellied woodpeckers (Melanerpes carolinus) from
the Apalachicola National Forest in Florida. Journal of
Parasitology 88(6):1140-1142.
|
