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.
Ecological
Constraints, Reproductive Skew, and the Evolution of Cooperative
Breeding in the 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 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. Males compete to mate
and females lay their eggs communally in the same nest. Cobreeders of the same
sex are almost always close relatives, either siblings or parents and
offspring. The project tests experimentally the role of roosting / 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 also involves
a study of reproductive skew among cobreeding males. Previous
work revealed that joint-nesting groups of females, unlike
males, share parentage equally. Through experiments, behavioral
observations, and genetic analyses; we are attempting to
determine the factors that influence reproductive sharing in
acorn woodpecker societies. A primary goal of this study is to
understand the fitness consequences of cooperative breeding and
to integrate findings into the larger questions of the evolution
and ecology of group living in highly social species like acorn
woodpeckers and humans.
Koenig, W.D., E.L. Walters, J. M.H. Knops, and W. J. Carmen. 2015. Acorns and acorn woodpeckers: ups and downs in a long-term relationship. Pp. 23-33. In [Standiford, Richard B.; Purcell, Kathryn L., tech. cords]. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 579 p.
Koenig, W.D., E.L. Walters, I.S. Pearse, and J.M.H. Knops. 2014. Serotiny in California oaks. Madroño 61:151-158.
We hire field assistants year
round. If interested, see
our employment
page.
Seed Dispersal
Avian Seed Dispersal Ecology in the Wet Forests of the Dominican Republic
My graduate student, Spencer Schubert, is studying seed dispersal (the movement of seeds away from the parent plant) within tropical forests of the Dominican Republic. Several fruiting species produce a crop multiple times per year and Spencer is trying to determine why such a strategy has evolved. He is also examining the network of frugivore mutualists and their role in determining the biodiversity of wet forests in the region.
The role of generalist avian frugivores in determining the distribution of the mistletoe
My graduate student, Nick Flanders, is examining the role of frugivorous birds in the dispersal and distribution of oak mistletoe (Phoradendron leucarpum). Through this project, Nick aims to further develop his understanding of plant ecology, interactions between birds and plants in the southeastern US, and the use of occupancy models to estimate bird distributions.
The role of hackberry (Celtis occidentalis) as a keystone resource for fall migrant songbirds
My graduate student, Chance Hines, is studying the role of hackberry (Celtis occidentalis) as a keystone resource within migrant songbird stopover habitat. Through a mutualism with hackberry gall psyllids, hackberry trees indirectly create species-rich patches of fruiting plants that are used by migrant songbirds during stopovers in the auturmn.
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.
Walters, E.L. Submitted. Unintended consequences of competitor removal: Markov chain community development models reveal hidden relationships. Journal of Animal Ecology.
Estimating
species interactions in a woodpecker tree-hole community at
the individual, population, and community levels
Collaborator: Frances C.
James (Florida State University)
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.
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.
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.
Urban Fragmentation and its Effect on
North America's Atlantic Migratory Flyway
ONGOING RESEARCH
Understanding the role of urban fragmentation on wildlife
movement patterns is critical to long-term conservation of
species using such areas. One of North America's most
important migration routes, the Atlantic Flyway, follows a
path directly over an urban area of 1.6 million people.
Hampton Roads, the 2nd largest port in North America, provides
important stopover habitat to millions of birds each year.
Fragmented patches of protected habitat are critically
important to many migratory species. Our work examines the
role that these habitat patches play for both resident and
migratory species within the urban matrix. The project also
involves a significant public outreach component whereby
members of the public get to experience bird banding up close
and get a better understanding of the suite of species that
rely on these remnants of habitat within a large major city.
Using NPOL/TOGA/NEXRAD Radar To Determine Habitat Use and Flight Paths of
Migratory Birds Along the Atlantic Flyway
Collaborators:
Jeff Buler (University of Delaware), Barry Truitt (The Nature
Conservancy), Deanna Dawson (USGS), Walt Petersen (NASA)
ONGOING RESEARCH
In
conjunction with NASA's ground validation dual polarimetric
radar (NPOL), we are studying migrant flight behavior along
Virginia's Eastern Shore. The radar will be based at the NSF
LTER site at Oyster and will be used by our research team to
study migrant movement behavior in the spring and fall along
Virginia's Delmarva Peninsula. More
info. Press
release.
Since
2013 we have been studying bird window kills. Up to a billion birds die per year in North America as a result of striking windows. We are conducting research at the Virginia Zoo and the Old Dominion University campus. We are also part of a national effort to look at nationwide trends in bird mortalities because of windows.
Collaborators:
Frances C. James (Florida State University); Charles A. Hess (US
Forest Service)
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.
Invasive
Species / New Records
Introduced in
1869, gypsy moths have invaded over 1 million square kilometers
of forest in North America. We examine the effects of this
massive disturbance event on North American woodpecker species.
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.
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)
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.
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.
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.
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)
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.,
E.H. Miller, and P.E. Lowther. 2014. Red-naped Sapsucker
(Sphyrapicus nuchalis). The Birds of North America Online (A. Poolel, Ed.). Ithaca: Cornell Lab of Ornithology; The Birds of North America Online. doi:10.2173/bna.663b
Walters, E.L.,
E.H. Miller, and P.E. Lowther. 2014. Red-breasted Sapsucker
(Sphyrapicus ruber). The Birds of North America Online (A. Poolel, Ed.). Ithaca: Cornell Lab of Ornithology; The Birds of North America Online. doi:10.2173/bna.663a
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
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 telemetry studies for over 23 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. We are currently using telemetry with Hispaniolan Woodpeckers and Palmchats in the Dominican Republic in addition to nanotags with our Acorn Woodpecker population.
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.
Collaborator:
Holly D. Gaff (Old Dominion University), Jory Brinkerhoff
(University of Richmond)
ONGOING RESEARCH
Avian
hosts likely play an important role in tick dispersal. Several
species of ticks in eastern Virginia
have
shown sudden and dramatic range shifts. These tick species act
as vectors of human disease and thus a complete understanding of
the role that avian hosts play in these range shifts is of
critical importance. Our research examines how both resident and
migratory avian species act as hosts to different tick life
stages at various
times of year. Our sampling occurs at several key locations in
Virginia in order to map the
progression of new tick species and the pathogens they carry as
they move deeper into Virginia.
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 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. Males compete to mate
and females lay their eggs communally in the same nest. Cobreeders of the same
sex are almost always close relatives, either siblings or parents and
offspring. The project tests experimentally the role of roosting / 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 also involves
a study of reproductive skew among cobreeding males. Previous
work revealed that joint-nesting groups of females, unlike
males, share parentage equally. Through experiments, behavioral
observations, and genetic analyses; we are attempting to
determine the factors that influence reproductive sharing in
acorn woodpecker societies. A primary goal of this study is to
understand the fitness consequences of cooperative breeding and
to integrate findings into the larger questions of the evolution
and ecology of group living in highly social species like acorn
woodpeckers and humans.
My graduate student, Spencer Schubert, is studying seed dispersal (the movement of seeds away from the parent plant) within tropical forests of the Dominican Republic. Several fruiting species produce a crop multiple times per year and Spencer is trying to determine why such a strategy has evolved. He is also examining the network of frugivore mutualists and their role in determining the biodiversity of wet forests in the region.
My graduate student, Chance Hines, is studying the role of hackberry (Celtis occidentalis) as a keystone resource within migrant songbird stopover habitat. Through a mutualism with hackberry gall psyllids, hackberry trees indirectly create species-rich patches of fruiting plants that are used by migrant songbirds during stopovers in the auturmn.
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. 
Species
assemblages are often dependent upon a discrete resource (e.g.
dung patches, 
2004.
Buckley, H., J. Burns, J. Kneitel, E.L. Walters, P. Munguia,
and T.E. Miller. 
ONGOING RESEARCH
Since
2013 we have been studying bird window kills. Up to a billion birds die per year in North America as a result of striking windows. We are conducting research at the Virginia Zoo and the Old Dominion University campus. We are also part of a 
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.
/ Species Management Plans
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. 
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.
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.,
E.H. Miller, and P.E. Lowther. 2014. Red-breasted Sapsucker
(Sphyrapicus ruber). The Birds of North America Online (A. Poolel, Ed.). Ithaca: Cornell Lab of Ornithology; The Birds of North America Online. doi:10.2173/bna.663a
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.
Schrader, M.S.,
E.L. Walters, F.C. James., and E.C. Greiner. 2003. 
Avian
hosts likely play an important role in tick dispersal. Several
species of ticks in eastern Virginia
have
shown sudden and dramatic range shifts. These tick species act
as vectors of human disease and thus a complete understanding of
the role that avian hosts play in these range shifts is of
critical importance. Our research examines how both resident and
migratory avian species act as hosts to different tick life
stages at various
times of year. Our sampling occurs at several key locations in
Virginia in order to map the
progression of new tick species and the pathogens they carry as
they move deeper into Virginia.
