![](media/image1.png){width="1.6861111111111111in"
height="1.4881944444444444in"}

######## 

######## U.S. Shorebird 

######## Conservation Plan

**National Shorebird**

**Research Needs**

A Proposal for a National Research Program and

Example High Priority Research Topics

May 2000

A Technical Report of the Research and Monitoring Working Group of the

U.S. Shorebird Conservation Plan

**This report should be cited as follows:**

Oring, Lew, Brian Harrington, Stephen Brown, and Catherine Hickey, eds.
2000. National Shorebird Research Needs: A Proposal for a National
Research Program and Example High Priority Research Topics. Manomet
Center for Conservation Sciences. http://www.Manomet.org/USSCP/files.htm

**Contributing Authors:**

Mary Anne Bishop, Prince William Sound Science Center

Cheri Gratto-Trevor, Canadian Wildlife Service

Susan Haig, USGS Forest and Rangeland Ecosystem Science Center

Brian Harrington, Manomet Center for Conservation Sciences

Rick Lanctot, USGS Alaska Biological Science Center

Todd Mabee, Colorado State University

David Mizrahi, Clemson University

Lewis Oring, University of Nevada, Reno

Laura Payne, University of Wisconsin

Nils Warnock, Point Reyes Bird Observatory

**Research Task Group Participants:**

Lew Oring, Chair, University of Nevada Reno

Mary Anne Bishop, Prince William Sound Science Center

Bob Gill, USGS Alaska Biological Science Center

Cheri Gratto-Trevor, Canadian Wildlife Service

Susan Haig, USGS Forest and Rangeland Ecosystem Science Center

Richard Lanctot, USGS Alaska Biological Science Center

David Mizrahi, Clemson University

Guy Morrison, Canadian Wildlife Service

Laura Payne, University of Wisconsin

Susan Skagen, USGS Midcontinent Ecological Science Center

**Table Of Contents**

[Introduction 1](#introduction)

[Program Administration 1](#program-administration)

[Example Priority Research Topics 2](#example-priority-research-topics)

[A. Essential research designed to facilitate stable and self-sustaining
shorebird populations, especially those of high national conservation
priority (ranks 5,4).
2](#a.-essential-research-designed-to-facilitate-stable-and-self-sustaining-shorebird-populations-especially-those-of-high-national-conservation-priority-ranks-54.)

[1. Identification of population limiting factors
2](#identification-of-population-limiting-factors)

[2. Distribution and abundance 2](#distribution-and-abundance)

[3. Space use and dispersal (including movements within and among years)
2](#space-use-and-dispersal-including-movements-within-and-among-years)

[4. Migration systems 2](#migration-systems)

[5. Turnover rates and stopover ecology
2](#turnover-rates-and-stopover-ecology)

[6. Energetics and foraging ecology 2](#energetics-and-foraging-ecology)

[7. Differentiation of sub-species and species
2](#differentiation-of-sub-species-and-species)

[B. Management research with application across regions.
3](#b.-management-research-with-application-across-regions.)

[1. Effects of global climate change.
3](#effects-of-global-climate-change.)

[2. Predator control. 3](#predator-control.)

[3. Disturbance. 3](#disturbance.)

[4. Increasing productivity. 3](#increasing-productivity.)

[C. Monitoring research and development of protocols for tracking
population trends.
3](#c.-monitoring-research-and-development-of-protocols-for-tracking-population-trends.)

[1. Population trends. 3](#population-trends.)

[2. Population fluctuations. 3](#population-fluctuations.)

[3. Research on the validity of sampling techniques.
3](#research-on-the-validity-of-sampling-techniques.)

[D. Other Priority Research Topics.
3](#d.-other-priority-research-topics.)

[Appendix 1. Descriptions of Selected Research Topics
4](#appendix-1.-descriptions-of-selected-research-topics)

[1) Critical Life History Information
4](#critical-life-history-information)

[A. Analysis of existing information on life histories and populations.
4](#a.-analysis-of-existing-information-on-life-histories-and-populations.)

[B. Collection of missing life history information for high priority
species.
4](#b.-collection-of-missing-life-history-information-for-high-priority-species.)

[2) Basic Research with Significant Conservation Implications
4](#basic-research-with-significant-conservation-implications)

[A. Shorebird distribution and abundance, including temporal and spatial
variation (Laura Payne)
4](#a.-shorebird-distribution-and-abundance-including-temporal-and-spatial-variation-laura-payne)

[B. Space Use and Dispersal (Sue Haig and Lew Oring).
5](#b.-space-use-and-dispersal-sue-haig-and-lew-oring.)

[C. Shorebird migration systems: origins, routes, and destinations of
specific populations (Guy Morrison)
7](#c.-shorebird-migration-systems-origins-routes-and-destinations-of-specific-populations-guy-morrison)

[D. Differentiation of sub-species and populations (Rick Lanctot)
10](#d.-differentiation-of-sub-species-and-populations-rick-lanctot)

[E. Turnover rates and stopover ecology (Nils Warnock and Mary Anne
Bishop)
12](#e.-turnover-rates-and-stopover-ecology-nils-warnock-and-mary-anne-bishop)

[3) Identification of Population Limitations (Cheri Gratto-Trevor)
14](#identification-of-population-limitations-cheri-gratto-trevor)

[A. Factors influencing productivity and breeding success
14](#a.-factors-influencing-productivity-and-breeding-success)

[B. Factors influencing juvenile and adult mortality
16](#b.-factors-influencing-juvenile-and-adult-mortality)

[4) Habitat Use, Quality, & Dynamics (Brian Harrington)
16](#habitat-use-quality-dynamics-brian-harrington)

[A. Habitat Distribution and Abundance
16](#a.-habitat-distribution-and-abundance)

[1. Means of identifying and assessing the quality of shorebird habitat
16](#means-of-identifying-and-assessing-the-quality-of-shorebird-habitat)

[2. Means of cooperation with other initiatives to track the
distribution of wetland and waterbird habitats
19](#means-of-cooperation-with-other-initiatives-to-track-the-distribution-of-wetland-and-waterbird-habitats)

[B. Migration Stopover Sites 19](#b.-migration-stopover-sites)

[1. Identification of characteristics of migratory stopover sites that
correlate with high use by shorebirds
19](#identification-of-characteristics-of-migratory-stopover-sites-that-correlate-with-high-use-by-shorebirds)

[2. Specific environmental risks associated with changes in habitat
characteristics
20](#specific-environmental-risks-associated-with-changes-in-habitat-characteristics)

[5) Management Research 20](#management-research)

[A. Assessment of population limiting factors
20](#a.-assessment-of-population-limiting-factors)

[B. Research to design techniques for reducing specific population
limiting factors
21](#b.-research-to-design-techniques-for-reducing-specific-population-limiting-factors)

[1. Management techniques to protect nesting shorebirds (Todd Mabee)
21](#management-techniques-to-protect-nesting-shorebirds-todd-mabee)

[2. Evaluating created wetland habitats for migrating shorebirds (David
Mizrahi)
23](#evaluating-created-wetland-habitats-for-migrating-shorebirds-david-mizrahi)

[Literature Cited 27](#literature-cited)

# Introduction

Populations of many of North America's 52 shorebird species are in steep
decline. In order to reverse these declines, and to assure stable,
self-sustaining populations, fundamental knowledge of shorebird biology
is essential. However, vast gaps exist in our knowledge of North
America's shorebirds. For example, for only a few of the rarest species
is there a scientifically valid estimate of population size. In
addition, the factors limiting the populations of most species are
unknown. Maintenance of stable and self-sustaining shorebird populations
is the central goal of the National Shorebird Research Program (NSRP)
proposed here. Shorebird conservation efforts cannot succeed in the
absence of sound knowledge on various aspects of shorebird biology.

As information on shorebird biology unfolds, it is difficult to predict
what topics will emerge as key issues for conservation. For example,
population declines may turn out to have sources in breeding areas,
along migration routes, or on the wintering grounds, or even a
combination. Issues such as acid rain, pollution, global warming, or
habitat loss might be involved, or other issues not presently recognized
may be key. Alternatively, with improved information, we may discover
that some declines that originally appeared to be alarming are actually
the results of natural population fluctuations.

In order to provide the up-to-date, scientifically rigorous information
essential for shorebird conservation, the U. S. Shorebird Conservation
Plan recommends the institution of the NSRP. This program will support
essential conservation based research on shorebirds through
establishment of a competitive grants program administered by the
Biological Resources Division of the United States Geological Survey,
acting upon the recommendation of a panel of experts. The program should
include annual funding of \$2 million for national research priorities,
and \$1.75 million for regional research priorities.

# Program Administration

The NSRP will be administered at USGS Patuxent Wildlife Research Center.
It may be necessary to utilize some proportion of new research funding
to hire support staff. The program administrator, a USGS employee, will
work with the Shorebird Planning Council to identify panel members, each
with the highest scientific credentials and possessing skills
representative of various research areas, e.g. breeding and non-breeding
biology, coastal and inland areas. The makeup of the panel will include
a Chair named by USGS and eight additional shorebird experts named by
the Shorebird Planning Council. The panel and the program administrator
will develop proposal guidelines and operating procedures, following as
closely as possible the guidelines used by the National Science
Foundation.

The function of the panel is to assure that funds are spent in a manner
most likely to enhance the goal of assuring stable and self-sustaining
shorebird populations. Proposals submitted to the NSRP will have the
obligation of convincing the evaluation panel that they will contribute
knowledge important to the restoration or maintenance of stable
shorebird populations. The panel will have the obligation of ranking
proposals on the basis of their likelihood to enhance shorebird
conservation through restoration or maintenance of stable populations.
The panel will have the national shorebird conservation priorities as a
guide in prioritizing proposed research. Partnerships among federal,
state, non-governmental organizations, and academic scientists will be
encouraged where this is logical for achieving the goal of stable and
self-sustaining shorebird populations.

While the goal of this program is population based, this in no way
infers that high priority research could not be funded at other levels,
such as mechanistic research dealing with the behavior or physiology of
shorebirds, their prey and predators; community, ecosystem or landscape
level ecology, etc. But, in the end, the goal is to maintain stable and
self-sustaining populations. Therefore, mechanistic, community,
ecosystem, or landscape proposals all have the obligation of
demonstrating their relevance to conservation of shorebird populations.

In addition to the 2M requested for the NSRP, 1.75 M has been requested
to support regional research. Just as the national shorebird community
has established national conservation priorities, regional groups are
ranking conservation priorities of species within regions. Sometimes
these are concordant with national priorities, sometimes they are
different. Regional support should be sought for research primarily of
importance relative to regional conservation priorities, or for
monitoring or management research primarily of regional application.

# Example Priority Research Topics 

## A. Essential research designed to facilitate stable and self-sustaining shorebird populations, especially those of high national conservation priority (ranks 5,4).

Persons proposing this research accept the responsibility of elucidating
how it will help lead to stable and self-sustaining shorebird
populations. Research aimed primarily at species/subspecies of low
national conservation ranking but high regional ranking should seek
funding through local/regional programs. Categories below overlap
broadly since avian life history necessarily involves multiple factors
at the same moment in time or space. Proposals for development of new
techniques broadly applicable to the topics below are encouraged.

### 1. Identification of population limiting factors

What limits the size of shorebird populations, especially for species of
concern?

Understanding the answer is basic to developing sound conservation
strategies.

a\. Factors influencing productivity/breeding success

b\. Factors influencing both juvenile and adult mortality (including
predation, environmental toxicants)

c\. Disturbance as a factor affecting \"a\" and \"b\" above, as well as
predation risk.

### 2. Distribution and abundance

Understanding patterns of shorebird distribution and abundance, and
factors controlling them. Research to improve monitoring activities
would fit in this area, but activities specifically aimed at monitoring
population trends are addressed under priority monitoring programs.

### 3. Space use and dispersal (including movements within and among years)

Exploration of factors affecting space use and dispersal decisions,
including the relationship of key habitat features such as foraging
benefit, predator risk, and information acquisition to relative use of
space.

### 4. Migration systems

Increasing our understanding of the dynamics of migration patterns,
including how populations move among sites, and why.

### 5. Turnover rates and stopover ecology

Understanding the timing of landscape level habitat use, which is
critical for monitoring studies, and understanding factors affecting
turnover rates.

### 6. Energetics and foraging ecology

Analysis of dietary requirements, elucidation of dietary preferences,
nutritional requirements, and metabolic needs.

### 7. Differentiation of sub-species and species

Identifying geographic population subdivision, determining conservation
issues below the species level, and identification of the role of
subspecies in the overall population dynamics of a species.

## B. Management research with application across regions.

Research proposals in this area must establish broad applicability to
enhancing shorebird populations across multiple regions, and includes
technique development where applicable to managing shorebirds.

1\. Controlling population limiting factors.

Research designed to develop techniques for reducing specific population
limiting factors, e.g., techniques for reducing nest predation, reducing
risks from toxicants, and improving or providing habitat.

### 1. Effects of global climate change.

Modeling potential impacts of and development of management protocols to
mitigate effects of global climate change.

### 2. Predator control.

Development of techniques to deter predators, e.g., including aversive
conditioning to reduce losses from both avian and mammalian predators.

### 3. Disturbance.

Disturbance effects on foraging and breeding, including measuring
disturbance impact and/or studying ways of reducing disturbance.

### 4. Increasing productivity.

Techniques for increasing productivity, including, captive breeding
reintroduction and associated techniques.

## C. Monitoring research and development of protocols for tracking population trends.

Research proposals in this area should identify how the projects can
lead to improved monitoring of species of national conservation concern
and/or development of techniques widely applicable across species.
Identification of sites used, habitats used, and variation across time
and space is primarily a monitoring activity and should be supported
with monitoring funds. However, development of new techniques for
analysis of monitoring data is highly appropriate for funding from this
program, including:

### 1. Population trends.

Development of models to predict population trends;

### 2. Population fluctuations.

Exploration of population fluctuations, and their impact on estimates of
numbers using sites; and

### 3. Research on the validity of sampling techniques.

## D. Other Priority Research Topics.

The topics outlined above are meant to be illustrative, not all
inclusive. Any research proposal judged by the Panel as likely to
provide knowledge of high value for enhancing stable and self-sustaining
shorebird populations is suitable for this program. One specific
additional topic identified by the working group as high priority is a
detailed literature review of existing life history information by
species, noting important gaps in knowledge on the following topics:

A. Distribution and abundance, including temporal and spatial variation

B. Energetics, diet and foraging behavior

C. Shorebird migration systems: origins, routes and destinations of
specific populations

D. Genetic variation within and between populations

E. Population dynamics, including:

1\. natality including factors affecting variation

2\. hatching/fledging, including factors affecting variation

3\. recruitment, including factors affecting variation

4\. longevity/survival, including factors affecting variation

5\. dispersal

# Appendix 1. Descriptions of Selected Research Topics

This appendix provides 5 examples of research topics of current interest
to development and implementation of National Shorebird Research
Priorities. These are intended to be illustrations of topics where
compiled information would benefit national shorebird conservation
planning.

## 1) Critical Life History Information

The maintenance of viable shorebird populations requires a long term
balance between recruitment and mortality. For species that have already
declined significantly from historic populations, restoration requires
that recruitment exceed mortality. Assessment of whether or not these
goals are being attained, and development of plans to increase
populations, requires baseline data on such factors as distribution and
abundance, natural variation in population sizes and distribution
patterns, and detailed knowledge of population limiting factors.
Therefore, the first priority for shorebird research is completion of a
species by species review of life history data including distribution
and abundance, and aspects of population dynamics such as age at first
breeding, hatching and fledging success, survival to reproductive age,
longevity, causes of mortality, geographic and annual variation of
populations, and interconnectedness of populations. This project is
described in section A. below, followed by recommendations for
collection of missing information on high priority species.

### A. Analysis of existing information on life histories and populations.

A considerable amount of research has been conducted on many species of
shorebirds to describe their basic life history characteristics.
However, there has never been a comprehensive analysis of the areas
where information critical to conservation is missing, even for many
high priority species. This section describes the elements that should
be addressed in a project designed to collect existing life history
information, and to locate and prioritize the most critical information
needed to effectively manage particular species:

1\. Distribution and abundance, including temporal and spatial variation

2\. Energetics, diet, and foraging behavior

3\. Interconnectedness of breeding, post-breeding, migrating, and
wintering populations

4\. Genetic variation within and between populations

5\. Population dynamics, including:

a\) Natality, including factors affecting variation

b\) Hatching/fledging including factors affecting variation

c\) Recruitment, including factors affecting variation

d\) Longevity/survival, including factors affecting variation

e\) Dispersal

### B. Collection of missing life history information for high priority species. 

Filling in missing information for high priority species should be a
primary research focus, especially for species with high conservation
priority rankings.

## 2) Basic Research with Significant Conservation Implications

### A. Shorebird distribution and abundance, including temporal and spatial variation (Laura Payne)

***Classification of distribution, density, and habitat specificity***.
The success of conservation and management programs depends to a large
extent on how much prior information we have on the distribution and
abundance of each species. To identify important gaps in our knowledge
of distribution and abundance, shorebirds should be classified according
to distribution, density, and habitat specificity, and also including a
measure of the level of confidence in the classification of each
species. In some cases it may be useful to make separate matrices for
breeding season, migration, and/or winter season.

Species with sparse population density, extensive range, and broad
habitat specificity may be threatened by gradual loss of habitat (such
as conversion of wetlands to agriculture) in the interior U.S., while
species with a dense population, restricted range, and narrow habitat
specificity may be threatened by oil spills or beachfront development in
the coastal U.S. This project will help prioritize future conservation
efforts by classifying species. Which species (or guilds, or types of
species) are well covered, and which are not? In which cases are
species-based approaches necessary, given that most efforts to date are
site-based?

***Landscape scale distribution***. Most of our knowledge of shorebird
migration has come from specific geographic locations, without the
benefit of an overriding landscape-scale perspective. Consequently, our
assumptions about how shorebirds use the landscape are influenced by the
scale at which we observe and census them. Research should be undertaken
to determine the scale at which shorebirds use the landscape, including
their local movements during breeding, migration (see Farmer and Parent
1997), and wintering.

***Anthropogenic effects on shorebird distribution***. Several
mechanisms have been proposed to explain (changes in) distribution and
abundance patterns of shorebirds. Further research should investigate
anthropogenic influences, whether through direct disturbance (see
Pfister et al. 1992), habitat alteration, or change in
landscape/community structure.

***Responses to changing habitat characteristics***. Some species show
consistent, year to year use of the same \'traditional\' sites
(especially in coastal areas). How flexible are these species to habitat
loss or long term changes? Does restored habitat attract these
shorebirds as effectively as it might their opportunistic, inland
congeners?

### B. Space Use and Dispersal (Sue Haig and Lew Oring).

Traditional shorebird conservation efforts have focussed on identifying
and protecting migratory stop-over sites where massive numbers of birds
pass through an area for a short period of time. In North America, this
tradition has continued as much of shorebird breeding takes place in
arctic regions where, until recently, habitat was thought to be
unharmed; and winter sites are only recently being recognized. However,
as more studies are conducted that examine how shorebirds use their
habitats within and among different phases of the annual cycle as well
as across years, we are learning the critical importance of having this
information prior to designing conservation strategies for species,
sites, or regions (Table 1).

For example, in the western Great Basin, individual American Avocets
move among multiple sites that can span hundreds of kilometers in
distance during the 2-4 months they spend post-breeding/pre-migration.
Conversely, Killdeer in the region will

generally stay within 1-3 km of their former nests sites for most of the
year, however, they use their immediate area far more than Avocets.
Thus, to design a regional conservation strategy that includes even just
two of the nine breeding shorebirds in the area, we need to consider
extensive areas around wetlands as well as a mosaic of wetlands that
offer alternatives for Avocets.

Similarly, the links between more distant sites used over various phases
of the annual cycle are important to identify. For example, Western
Sandpipers use of series of North American stopover sites and breeding
areas that range from Baja to western Alaska. Yet Western Sandpipers
that winter in San Francisco Bay have home ranges that average 22 km.
Thus, single-species efforts must take a multi-dimensional view that
links distant sites.

Finally, annual patterns of site use, regardless of the phase of the
annual cycle, can provide perspective on habitat quality and stability.
For example, each year sites such as the Great Salt Lake, Mono Lake, and
Lake Abert provide post-breeding/pre-migration habitat for hundreds of
thousands of shorebirds. Thus, it was important to recognize these sites
and their inter-linkages for species such as American Avocets, Wilson\'s
Phalaropes, and Red-necked Phalaropes. Conversely, during the breeding
season, species such as Piping Plovers, Buff-breasted Sandpipers, and
various phalaropes have widely-varying site fidelity that can range from
returning to local areas to moving hundreds of kilometers away. Thus,
they must be provided options for breeding when conditions change in
their highly dynamic environments.

Therefore, our conservation planning efforts from local to global must
consider and incorporate the vast diversity of space use among
shorebirds throughout the annual cycle. Included in these studies should
be efforts not only to describe patterns of space use but to address
hypotheses that will explain factors that contribute to space use
decisions, what limits space use, and what can be done to insure proper
conservation of the suite of sites needed for viable populations. Use of
color-marked birds, radio-telemetry, satellite telemetry,
population-specific molecular markers, and geographic information
systems will provide the tools necessary to address these issues.

### C. Shorebird migration systems: origins, routes, and destinations of specific populations (Guy Morrison)

Knowledge of what may be termed the migration system of a shorebird
species, involving an understanding of its breeding origins, migration
routes and wintering destinations, is a basic requirement for
conservation. Knowledge of how populations move between sites and which
sites are linked is important in ensuring that all the areas needed by
the birds to complete their annual travels are adequately protected.

While the broad outline of the migration systems used by many species
may be understood, detailed knowledge exists for remarkably few species,
and even for those, is often incomplete. Shorebirds exhibit a variety of
migration systems and strategies. Table 1 shows a general categorization
of shorebirds according to whether they are principally coastal or
inland migrants (in North America, note many species occur in both types
of habitat, though usually one predominates), according to migration
distance (long, intermediate, short) and flyway/coast occurrence. Note
that coastal migrants are generally gregarious, occurring in large
flocks during migration and wintering periods, while inland migrants
tend to include solitary or more dispersed species.

General Approach: While it is desirable to have a clear knowledge of
migration links for all species, a more practical approach may be to
focus on a number of "flagship" species that move between many of the
key areas situated in the various flyways. This approach has proved
effective in elucidating links between sites for a number of species,
including Red Knot, Sanderling, Semipalmated Sandpiper and Western
Sandpiper. A number of potential flagship species are indicated in bold
in Table 2.

Methods. Traditional methods of investigating migration patterns have
involved banding and color-marking shorebirds, and these continue to be
effective, if time consuming and labor intensive, for many species. New
techniques need to be used and developed. Radio tracking has proved very
instructive in showing long-distance movements of Western Sandpipers
along the Pacific Flyway and is being developed for Red Knots along the
Western Atlantic Flyway. Satellite telemetry has almost reached the
point where it can be used for shorebirds, though available units are
still potentially rather heavy to place on long-distance migrants:
development of smaller units and/or lighter power sources will
revolutionize the study of shorebird migration and should be pursued. A
variety of "molecular" methods are available by which populations and
sub-populations may potentially be identified, including DNA techniques
and methods involving analysis of stable isotopes. Combination of these
methods will provide insight into movements of populations,
sub-populations, sexes etc.

Recommendation. A number of flagship species which use major sites in
all geographical regions and flyways should be chosen for study, and an
integrated program involving traditional and new techniques developed to
elucidate movement patterns of all segments of the population in
relation to ecological requirements at all stages of the annual cycle.

Table 2. Migration systems of shorebirds, showing principal
flyway/coast(s) used and migration distance for species that occur
principally in coastal or inland habitats. Species that tend to be
dispersed, or occur either solitarily or in small flocks are in italics.
Some suggested "flaghip" species representative of different categories
are indicated in bold.

  -------------- ---------- ---------- ----------------- --------- ------------------ ----------
  **Coastal**                                                                         

                 Both       Pacific    Central-Pacific   Central   Central-Atlantic   Atlantic

  Long           **SAND**   **PGPL**                               **HUGO** RUTU      **REKN**
                 RNPH REPH  SHSA WATA                                                 
                            SURF                                                      

  Intermediate   BBPL SEPL  **WESA**                                                  **SESA**
                 LESA       LBDO                                                      
                 **DUNL**                                                             
                 SBDO WHIM                                                            

  Short          **WILL**   BLOY BLTU                              AMOY               **PUSA**
                            ROSA                                                      
  -------------- ---------- ---------- ----------------- --------- ------------------ ----------

  -------------- ---------- --------- ----------------- ---------- ------------------ ----------
  **Inland**                                                                          

                 Both       Pacific   Central-Pacific   Central    Central-Atlantic   Atlantic

  Long                                                  BASA       AGPL ESCU **WRSA** 
                                                        **WIPH**                      
                                                        PESA                          

  Intermediate   *GRYE LEYE                             *SOSA*     *UPSA*             
                 SPSA*                                                                

  Short          *KILL*               *SNPL* AMAV       *MOUP*     *WIPL **PIPL**     
                 **BNST**             *LBCU* **MAGO**              AMWO*              
                 *COSN*                                                               
  -------------- ---------- --------- ----------------- ---------- ------------------ ----------

### D. Differentiation of sub-species and populations (Rick Lanctot)

Monitoring shorebird population trends, distribution, and abundance is
one of the top priorities of the Shorebird Plan. Essential to this goal
is the ability to identify geographically distinct subspecies and/or
populations. This section describes the merits of identifying geographic
population subdivision (or phylogeography), lists previous efforts to
identify populations within shorebird species, and lists future research
priorities.

Understanding geographic population subdivision is imperative given the
varied geographic distributions, life histories, and migratory pathways
of most shorebirds. Indeed, species (and perhaps populations within
species) may differ in their breeding and natal philopatry, winter
fidelity, migratory pathways, and location in which they winter. The
extent to which these factors contribute to genetic differentiation of
populations within species varies, and is relatively unknown for most
shorebirds. Phylogeographic structuring can have dramatic effects on how
species should be managed however. For example, high breeding site
fidelity and/or natal philopatry may result in genetically unique
populations which would require particular areas within a species range
be conserved to protect that portion of the breeding population.
Similarly, highly defined migratory pathways may require protection of
particular staging areas to ensure the species is able to complete their
annual flight.

Historically, ornithologists have relied on observational methods, such
as mark and recapture techniques or morphological comparisons, to
investigate contemporary gene flow or population distinctness within
shorebird species. These methods have provided valuable information in a
few cases, but have been generally difficult to conduct, unreliable
(i.e., few birds have been resighted), and/or expensive. The advent of
satellite transmitters has the potential to provide valuable information
on migratory movements, although current transmitter models are too
heavy for all but the largest of shorebirds. A variety of molecular
techniques have also been employed to estimate historic (and possibly
contemporary) gene flow among populations (Table 3). Most of these
studies, utilizing protein, mitochondrial DNA and minisatellite DNA
markers, have found low levels of population subdivision within
shorebirds. Haig et al. (1997), using random amplified polymorphic DNA
(RAPD) markers, found that population subdivision varied greatly within
breeding populations of nine migratory species sampled throughout North
America. Their results provided strong evidence for phylogeographical
structure, with population differentiation correlated with interspecific
variation in philopatry and geographic separation of breeding
populations. Recent molecular advances involve the use of the polymerase
chain reaction and microsatellite markers, although no data have been
published on North American shorebirds to date. A new avenue for
identifying the geographic origins of migratory bird species (and hence
the degree of mixing of breeding populations on migratory or wintering
sites) involves the use of stable isotopes (Chamberlain, et al. 1997).
Isotopes accumulated in the feathers of birds on their breeding groups
have the potential of acting as markers, much as colored tarsal bands
can identify the location a bird was captured. Undoubtedly, a
combination of the above methods should be used to accurately identify
the level at which species can be subdivided into definable management
units.

Given the limiting finances available to conduct phylogeographic
studies, it seems reasonable that future research be limited to
species 1) that are threatened or endangered in particular portions of
their breeding or wintering range, 2) whose members are distributed in
geographically distinct locations and whose relatedness is unknown, and
3) who have morphologically similar congeners whose taxonomic status is
questionable. Such efforts may prove valuable in defining subspecies or
populations within species, and consequently determining whether
segments of any one species should be managed separately and perhaps
preferentially from other segments.

Table 3. Molecular techniques employed to estimate population structure
in shorebirds.

  ----------------- ------------------------- ------------------ -----------------
  Genetic Marker    Species Tested            Conclusions        References

  Protein           *Calidris canutus, C.     Most species had   Baker and Strauch
  electrophoresis   maritima, C. minutilla,   low levels of      1988
                    C. fuscicollis, C.        within-species     
                    alpina, C. mauri,         genetic variation, 
                    Catoptrophorus            and resembled      
                    semipalmatus, Limnodromus large panmictic    
                    griseus*                  populations.       

                    *Charadrius melodus*      Little population  Haig and Oring
                                              differentiation.   1988

  Random amplified  *Limnodromus scolopaceus, Phylogeographic    Haig et al. 1997
  polymorphic DNA   L. griseus, Limosa        structured varied  
  (RAPD)            haemastica, Phalaropus    among species and  
                    lobatus, Charadrius       correlated with    
                    semipalmatus, Calidris    variation in       
                    alpina, C. melanotos, C.  philopatry and     
                    pusilla, C. mauri*        geographical       
                                              separation of      
                                              breeding           
                                              populations.       

                    *Scolopax rusticola*      Support migration  Burlando et al.
                                              patterns based on  1996
                                              banding data.      

  Mitochondrial DNA *Arenaria interpres,      *A. interpres*     Wenink et al.
                    Calidris alpina*          populations are    1994
                                              unstructured,      
                                              whereas *C.        
                                              alpina* show       
                                              genetic structure. 

                    *Calidris alpina*         Five major         Wenink et al.
                                              phylogeographic    1996
                                              groups identified. 

  Minisatellite DNA *Actitis macularia*       Little             Reed et al. 1996
                                              differentiation    
                                              between two        
                                              populations in     
                                              center of range.   

  Microsatellite    *Haematopus ostralegus*   No population      Treuren et al.
  DNA                                         structure.         Submitted

  Stable Isotopes   No shorebirds to date.    No information     Chamberlain et
                                              available.         al. 1997
  ----------------- ------------------------- ------------------ -----------------

### E. Turnover rates and stopover ecology (Nils Warnock and Mary Anne Bishop)

Understanding the stopover ecology of shorebirds is a critical component
of understanding the complete life cycle of these birds. Conservation of
migratory stopover sites relies not only on knowing how and when
different areas of their migration landscape are used, but also on
knowing what influences the use of and time spent at different areas of
that landscape (Warnock and Bishop 1998). Most monitoring efforts
require some understanding of turnover rates of shorebirds at different
sites, since without these data interpretive power of count data and
accurate estimation of maximum population sizes using sites and regions
are weakened (Warnock et al 1998). Recent work in the Great Plains of
North America has emphasized the importance of understanding length of
stay of shorebirds by demonstrating that although small, scattered
wetlands may support small numbers of shorebirds at a single time, when
combining use of small wetlands over a region and factoring in rapid
turnover, large numbers of shorebirds are actually using the flyway
(Skagen and Knopf 1994, Farmer and Parent 1997, Skagen 1997). Until
recently length of stay of shorebirds has largely been estimated through
resightings of marked birds, but advances in the miniaturization of
radiotransmitters have resulted in more accurate estimates of length of
stay at banding and stopover sites (Skagen and Knopf 1994, Iverson et
al. 1996, Warnock and Bishop 1998). Calculations of length of stay of
shorebirds other than *Calidris* sandpipers at migratory stopover sites
are largely lacking and urgently needed.

***Length of stay of some North American Sandpipers***

Table 4 lists published length of stay information for some sandpipers.

***Factors affecting length of stay*** (from Warnock and Bishop 1998).
Numerous studies have examined the relationship between indexes of body
condition of migrant shorebirds to length of stay at stopover sites
(e.g. Skagen and Knopf 1994, Lyons and Haig 1995, Iverson et al. 1996).
Warnock and Bishop (1998) found no relationship between length of stay
and body condition of birds at their banding sites. However, they
detected a small but significant trend for body condition at the banding
site of male Western Sandpipers to be correlated with length of stay at
the Copper River Delta. Adult, male Western Sandpipers tend to arrive
slightly earlier at the breeding grounds than females, just as snow
begins to melt (Holmes 1971). Earliest arrivals to sub-Arctic and Arctic
breeding grounds encounter greater uncertainties in weather (Green et
al. 1977) and food availability (Holmes 1972), forces that will select
for birds in better body condition.

However, body condition of migrating shorebirds at time of capture
generally explains little of the variation in the length of stay of
birds at stopovers (Skagen and Knopf 1994, Lyons and Haig 1995, Iverson
et al. 1996, Warnock and Bishop 1998), and other factors need be
considered. Wind conditions could mask effects of body condition on
length of stay at stopover sites (Holmgren et al. 1993), and may be an
important influence on length of stay for some species of shorebirds
(Butler et al. 1997). Skagen and Knopf (1994) failed to detect effects
of wind on the departures of migrating Semipalmated Sandpipers (*C.
pusilla*), but in one year they found White-rumped Sandpipers departing
more often on northerly winds. Western Sandpipers appear to be unable to
make the migration movement from San Francisco to Alaska given the time
they do it in (Iverson et al. 1996) and their body conditions without
assistance from wind (Butler et al. 1997). Other factors likely
influence length of stay of shorebirds at stopover sites. Two such
factors are arrival date and sex. Semipalmated Sandpipers (Dunn et al.
1988, Lyons and Haig 1995), Little Stints (*C. minuta*, Keijl et al.
1992), and White-rumped Sandpipers (in one of two years, Skagen and
Knopf 1994), have shorter length of stays as the migration progresses.
Male Semipalmated Sandpipers have shorter length of stay in spring than
females (Skagen and Knopf 1994, Lyons and Haig 1995). Warnock and Bishop
(1998) failed to detect differences in length of stay of Western
Sandpipers at banding sites based on date or sex. However, at one
stopover site, the Copper River Delta, the last major stopover site
before the breeding grounds, the later in date a male arrived, the
shorter he stayed. No pattern was detected for females. In Spain, male
Curlew Sandpipers had longer lengths of stay than females (Figuerola and
Bertolero 1998).

Shorebirds migrating towards breeding grounds in the sub-Arctic and
Arctic face time constraints, and males probably face tighter
constraints than females the closer they get to the breeding grounds, as
has been suggested for Western Sandpipers (Warnock and Bishop 1998).
Early arrivals may fledge more young than late arrivals as is seen with
female, polyandrous Spotted Sandpipers (*Actitis macularia*, Oring and
Lank 1986). Females also face time constraints. Eggs laid too early in
the season face freezing (Green et al. 1977), while for chicks hatching
too late in the short breeding season there is an increased probability
of food shortages (Holmes 1972) and, in some years, greater predation
(Oring and Lank 1986, Jönsson 1991). However, energetic costs for
females may be equally or more important than time considerations
because egg production is energetically expensive (MacLean 1969, Blem
1990).

A potential influence on length of stay is prey depletion at stopover
sites. At some sites, it has been shown that shorebirds impact
invertebrate populations over the migration period (Schneider and
Harrington 1981, Wilson 1989). Prey depletion at stopover sites by
Western Sandpipers is not thought to affect length of stay (Warnock and
Bishop 1998). Migration season (Fall vs. Spring) may influence the
length of stay of some shorebirds, but this remains to be properly
tested.

## 3) Identification of Population Limitations (Cheri Gratto-Trevor)

To effectively manage, enhance or maintain shorebird populations we need
to understand their population dynamics: factors affecting their
productivity and survival. Some similarities exist among species (e.g.
most North American shorebirds lay clutches of 4 eggs on the ground),
but many other aspects differ according to mating system, taxonomic
group, species size, latitudinal distribution, coastal versus interior
habitat, annual variation in climate and predator regimes, and so on
(Pitelka et al. 1974, Evans and Pienkowski 1984, Whitfield 1985, Helmers
and Gratto-Trevor 1996). We need to know whether populations of
shorebirds in decline are most affected by changes in productivity or
survival (and immigration/emigration), where the greatest effects occur,
and why. Some of this information exists for some species in some areas,
but much is lacking (e.g. Table 5).

### A. Factors influencing productivity and breeding success

For many shorebird species, estimates of year to year variation in
hatching rates exist (e.g. Table 5). Fewer studies provide information
on fledging rates, or numbers hatched or fledged per adult female
(including annual variation in mate acquisition and non breeding).
Almost no shorebird studies have determined survival from hatch to age
of first breeding. Average age of first breeding itself (including sex
and annual differences) is unknown for many species. Rates of natal
philopatry and dispersal are virtually unknown (Evans and Pienkowski
1984, Thompson et al. 1994). Due to this lack of information, it is
difficult to produce useful models to examine the potential effects of
changes in productivity, breeding biology, and survival on population
trends. Reasons for year to year variation in productivity have been
examined in some species, and some general conclusions can be drawn
about the effects of disturbance, weather, changes in predator regimes,
etc. in some habitats (e.g. Evans and Pienkowski 1984). The importance
of microtine cycles (with shorebird eggs and chicks as alternative prey
in low microtine years) has been demonstrated in some parts of the
arctic (Summers and Underhill 1987, Sutherland 1988), but whether such
factors are important in other regions such as the prairies is unknown.
A few studies have discussed potential effects of climate change on
shorebird populations (Lester and Myers 1991, Gratto-Trevor 1997), but
more information is necessary.

Table 5. Population demography information for selected shorebird
species: those with Birds of North America accounts. Average nest
success=% nests with \> 1 hatched/total nests, range from different
studies, in parentheses=%eggs hatched/total eggs. Average fledging
success=fledged chicks/chicks hatched, range from different studies.
Annual adult survival estimate from computer program. This is not
intended to include all studies where multiple datasets exist on the
same factor.

  --------- --------- --------- ---------- ---------- ---------- -------- ---------- ---------------
  Species   Average   Ave. nest Ave.       Ave.       Survival   Annual   Annual     Reference
                                fledging              to         adult    adult      

            mass (g)  success   success    1st        1st summer return   survival   
                                           breeding              rate     est.       

  LESA      23        57-90+%   40%        1                     52%                 Miller 1983,
                                                                                     Cooper 1994

  SESA      28        50%       50%        2-3                   47%      59%        Gratto-Trevor
                                                                                     1992,
                                                                                     Sandercock and
                                                                                     Gratto-Trevor
                                                                                     1997

  SNPL      41        53%       40%        1                     75%      58-88%     Page et al.
                                                                                     1995

  SPSA      46        (51%)     83%        1?                    63%?                Oring et al.
                                                                                     1997

  SOSA      48                                                                       Moskoff 1995

  WRSA      50                                                                       Parmelee 1992

  PIPL      54        34%       \~82%      1                     66%      66%        Haig 1992, Haig
                                                                                     and Oring 1988

  DUNL      58        30%       36%        2          33%        72%      74%        Warnock and
                                                                                     Gill 1996,
                                                                                     Warnock et al.
                                                                                     1999

  STSA      58        53-92%    \<50%                            73%                 Klima and Jehl
                                                                                     1998

  WIPH      60        33%                  1                     19%                 Colwell and
                                                                                     Jehl 1994

  BBSA      63        40%       28%                              12%                 Lanctot and
                                                                                     Laredo 1994

  PESA      81        62-71%                                     6%                  Holmes and
                                                                                     Pitelka 1998

  MOPL      95        26-65%    25-35%?                                              Knopf 1996

  AMWO      135       58%       90%?       1          59%        40%      60%        Keppie and
                                                                                     Whiting 1994

  AMGP      152       50-70%               1                     76%                 Johnson and
                                                                                     Connors 1996

  GRYE      153                                                                      Elphick and
                                                                                     Tibbitts 1998

  SURF      202                                                                      Senner and
                                                                                     McCaffery 1997

  BBPL      220       58-65%               2?         63%        89%                 Paulson 1995

  AMAV      312       40%       38%        2          58% (to    83-86%              Robinson et al.
                                                      2S)                            1997

  ESCU      375                                                                      Gill et al.
                                                                                     1998

  WHIM      404       48%       32%        3                                         Skeel and
                                                                                     Mallory 1996

  BLOY      555       54-62%    32-82%     5                     90%                 Andres and
                                                                                     Falxa 1995

  AMOY      602       72%       34-80%     3-4                   85%                 Nol and
                                                                                     Humphrey 1994
  --------- --------- --------- ---------- ---------- ---------- -------- ---------- ---------------

### B. Factors influencing juvenile and adult mortality

We have some estimates of survival rates, mostly for adults, primarily
based on return rates that confound philopatry and survival (e.g. Table
5). A computer model of population trends in Semipalmated Sandpipers was
very sensitive to even slight changes in adult survival (and
emigration/immigration) compared to large changes in productivity
(Hitchcock and Gratto-Trevor 1997). If this is true for one of the
smallest shorebirds it seems likely to be so for most other shorebird
species, especially those with considerable year to year variability in
productivity and/or delayed age of first breeding. If even slight
changes in adult survival (and immigration/emigration) rates have such a
large effect on population trend, we need better estimates of adult
survival (e.g. using modern computer programs such as Surge or Mark -
although even those cannot correct for birds that permanently emigrate,
e.g Warnock et al. 1999) and movements among breeding populations for
most shorebird species (Haig ?). We need to know where mortality is
occurring in the life cycle, in what locations and why - whether
declines have occurred due to anthropogenic changes in habitat (e.g.
power lines, predator regimes, disturbance, etc.). Particularly for
endangered species, population trends should be modeled, to determine if
increases in productivity possible through management can conceivably
offset even slight declines in adult survival. It is possible that
management efforts would be better directed towards improving adult
survival than improving productivity.

## 4) Habitat Use, Quality, & Dynamics (Brian Harrington)

### A. Habitat Distribution and Abundance

There are approximately 70 species of shorebirds found in North America,
roughly 50 of which occur regularly. Each species has its own food and
habitat requirements, and for most species, the requirements are
different between breeding, migration, and wintering seasons. In some
situations (varying with species, season and geographic season) species
may be quite labile in selection of food and/or habitat, whereas in
other cases they may be highly specialized. Outlining habitat research
requirements for shorebirds is an awesome challenge, demanding that a
process be identified that can be applied across species to find out
priority information needs. Habitat research priorities for the USSCP
aim to identify food and habitat information needs with respect to their
influences on population stability and conservation planning.

### 1. Means of identifying and assessing the quality of shorebird habitat

a\) [Breeding Habitat]{.underline}

A systematic research program is needed to identify amounts and
availability of breeding habitat of North American shorebirds with a
view to understanding whether amounts of habitat are limiting population
size. In the US SCP, priority is given to research for developing
mapping by using satellite or other aerial imagery. For each selected
species breeding habitat preferences needs to be identified and
characterized for signatures detectable with remote imagery. Amounts of
habitat within the breeding range of the species can then be evaluated.
Ground-based sub-sampling with a goal of quantifying breeding densities,
habitat amounts and locations can document effectiveness of the methods.
Priority should be given to species that use habitats thought to be
highly limited and/or in decline, for example Alaskan breeding habitat
of Bristle-thighed Curlews, short-grass prairie, alkalai basins, prairie
pothole, or coastal beaches.

Conditions of breeding habitat also can change from year-to-year,
depending for example, on rainfall amounts or (in Alaska and Arctic
Canada) spring snow conditions (Nol *et al.,* 1997). Some shorebirds
species, for example Pectoral Sandpiper, will shift breeding locations
as habitat (and other ?) conditions vary (Parmelee *et al.*, 1968),
whereas other species do not (Lappo, 1996). Relationships between annual
habitat conditions and annual breeding productivity of shorebird species
are poorly known. Annual shorebird breeding habitat conditions (e.g.
temperature and snow cover in Alaska, temperature and rainfall in the
Lower 48 states) should be monitored to establish how habitat conditions
relate to annual breeding production.

b\) [Non-breeding Habitat]{.underline}

Most shorebirds that breed in the U.S. migrate to wintering areas in the
Caribbean, Central and South America, in Oceania, or in the southern
United States. In many cases the nonbreeding period is almost a
continuum of movement, with southward migration requiring 1-4 months, a
2-4 month wintering period, and a 1-3 month northward migration period
(Morrison, 1984). Many kinds of shorebirds depend upon migration
stopover habitats in the United States, yet relatively small portions of
their populations may breed or spend winter in the U.S.

***Migration seasons***. Although there is little documenting research,
it is generally held that shorebirds are more limited by availability of
suitable habitat during migration than by availability of particular
prey types. For example, based on assessments of Skagen & Oman (1996),
it is clear that many kinds of shorebirds are quite variable in prey
selection during migration, taking advantage of foraging opportunities
as they develop at the right time and place. Frequently good migration
foraging opportunities are associated with changed habitat conditions,
for example lowering water levels in nonmarine wetlands that make
mud-dwelling invertebrate animals accessible to shorebirds (Safran *et
al.*, 1997). Other situations are more predictable, for example a
seasonal bloom of marine invertebrate animals at tidal coastal locations
(Schneider & Harrington, 1981).

The way in which shorebirds use migration stopover areas may also vary.
In some situations individuals may visit a stopover site only briefly
before quickly moving to another location ('short-hop' migrants , e.g.
American Avocets (Robinson & Oring, 1996). Other species visit stopover
sites for many days in order to lay on fat, muscle and other body
tissues needed for long-distance flights that may span hundreds or
thousands of miles without stops ('long-hop' migrants, e.g. White-rumped
Sandpipers (Harrington et. al., 1991).

A variety of studies show that food resources at migration staging areas
can be depleted by shorebirds (e.g. Schneider & Harrington, 1981); other
studies have not found prey depletion (Duffy *et al.* 1981). Those
situations where food depletion has been documented indicate that
migration habitat may be limiting to shorebird numbers. Moreover,
circumstantial information suggests that shorebirds unable to gain
sufficient fat at staging sites have higher mortality rates than those
that do (Pfister et al 1998). Notwithstanding this logic, it also is
possible that large fractions of a species population may use a single
staging site simply because it is a location with rich food resources
accessible at a strategic time. This does not preclude the possibility
that there is extensive alternative habitat available. In other
situations there is little pre-migration fattening as daily turnover
rates of birds are high (i.e. visitation periods by individual birds are
too short to enable pre-migration fattening, Butler *et al.,* 1987).

Research is needed on relationships between shorebirds' use of migration
staging sites, prey depletion, and population biology to identify
whether populations are affected by loss of migration stopover habitat.
This requires information on the migration strategies that different
species employ (migration duration, numbers of stopovers used) and
understandings of whether conditions at migration stopover areas have
important effects on populations. A good starting point will be to
compare dispersion patterns between shorebird species, identifying those
whose populations are most concentrated at small numbers of migration
and/or wintering areas. This should be followed with studies of resource
use and prey depletion patterns of the most highly concentrated species
to explore whether they are habitat-limited (studies also can
simultaneously examine other factors such as disease and predation).

Some shorebirds may employ more than one kind of migration strategy,
depending upon stage of migration and/or prevailing habitat conditions
(e.g. White-rumped Sandpiper, Harrington et al. 1991). Little is known
of whether/how shorebirds may change strategies. The question is
particularly important with respect to species migrating through regions
where habitat and food resources are unpredictable (Skagen & Knopf,
1994). For example, pothole prairie or playa lake habitat conditions can
vary enormously depending upon rainfall cycles; during some years water
levels are high in practically all wetlands, whereas only relatively
small numbers of wetlands are available during dry periods. There is
little information to suggest whether such variable landscape conditions
affect shorebird populations, both with respect to breeding species or
species in migration. Costs of doing this research are estimated at
\$2.5 million per year over a two decade period.

***Winter seasons***. There also is very little known of how winter
habitat conditions affect shorebird populations. Baker and Baker (1972),
in their classic studies, propose that shorebird populations may be more
limited by wintering habitat conditions than by breeding habitat
conditions.

Most of the shorebird species breeding in North America winter
principally south of the United States. Species that winter principally
in North America --and mostly in the U.S.\-- include Piping Plover,
Snowy Plover, Mountain Plover, Killdeer, Black and American
Oystercatcher, Black Turnstone, Purple and Rock Sandpipers, Dunlin, and
Common Snipe. A number of additional species have portions of their
populations wintering in the U.S., with most individuals wintering south
of the U.S.

Habitat research needed for predominately U.S.-wintering species. Little
is known of what makes good winter habitat for most of the species
listed above, possibly excepting ongoing research with Piping and
Mountain plovers. The balance of the listed species are all wintering in
coastal habitats, some (e.g. American Oystercatcher and Rock and Purple
Sandpiper) in relatively restricted zones where loss of key habitat
could potentially reduce population size by a serious degree. Research
needed should focus on developing a basic understanding of the feeding
and roosting habitat requirements.

U.S.-breeding shorebirds that winter predominately outside of the United
States include Wilson's and Snowy Plover , Black-necked Stilt, American
Avocet, Willet, Spotted Sandpiper, Upland Sandpiper, Long-billed Curlew,
Marbled Godwit, Surfbird\*\*, Western Sandpiper\*, Long-billed
Dowitcher\*, and Wilson's Phalarope. Several of these species
concentrate in relatively small wintering regions, and appear vulnerable
to loss of strategic wintering habitat. Research is needed in western
Mexico --especially in Sinaloa, Nayarit and Baja California del Sur\--
on habitat requirements of Black-necked Stilt, American Avocets,
Willets, Long-billed Curlews, Marbled Godwits, dowitchers and Western
Sandpipers (Morrison *et al.* 1993). Upland Sandpipers winter
principally in Argentina, but evidently are quite dispersed (Hayes *et
al*., 1990). \[Large numbers of Willets also winter in on the Atlantic
coast of South America between Guyana and eastern Brazil; it is unclear
whether these are mostly Eastern and/or Western Willets, but it is most
likely that they are the Eastern race. Little is known of their winter
ecology.\] Wilson's Phalarope winter principally in Chile and Argentina,
and evidently are concentrated in a relatively small number of lakes and
wetlands (Laredo, 1996). Research is needed to clarify their wintering
dispersion and habitat requirements for all of the above species and
groups.

### 2. Means of cooperation with other initiatives to track the distribution of wetland and waterbird habitats

Tracking the availability of wetland habitats is a monumental task that
will require cooperation among many diverse organizations, including all
of the bird conservation initiatives, federal land management agencies,
and the National Wetlands Inventory.

***Remote sensing of habitat**.* A research project should be undertaken
to determine utility of developing and implementing a large-scale
program (such as the use of satellite imagery \-- see Morrison 1997) for
determining or assessing distribution and abundance, and for in addition
to quantifying suitable habitat. Ideally, these methods could allow for
coarse-scale monitoring as well.

## B. Migration Stopover Sites

### 1. Identification of characteristics of migratory stopover sites that correlate with high use by shorebirds

Ideally the above review of habitat research needs would have been
focused on key habitats, and not on species. However, because so little
work has been completed on habitat requirements for most kinds of
shorebirds, it is premature to pick 'focal habitats' for special
attention. An exception exists with questions about migration stopover
area habitat, where enough research has been completed to begin asking
the right questions. Some of the key issues about migration stopover
habitats were introduced in the earlier sections, so here we introduce
additional habitat questions that should be answered in future research.

What makes a good migration stopover area? We know that many kinds of
shorebirds concentrate to an extraordinary degree at traditionally used
migration staging sites. We still do not know whether there are certain
attributes of these sites that make them a singular or strategic
resource, which if lost, would have serious impacts to shorebird
populations. A controversial example is the Delaware Bay staging area
used in spring by substantial fractions of continental Ruddy Turnstone,
Red Knot, Semipalmated Sandpiper, and Sanderling populations. No
information has been collected to explore whether alternative staging
sites exist for these species should Delaware Bay conditions change (as
is beginning to appear very likely).

Another example exists with Semipalmated Sandpipers during southward
migration. Studies in the 1970's and the 1980's (Morrison & Harrington,
1979 ) found high numbers for locations in New England. Today relatively
few use these same areas, evidently having shifted to using
invertebrate-rich shorelines near the head of the Bay of Fundy. Did the
New England locations become less useful due to invertebrate population
change, and/or did the Bay of Fundy sites somehow become more
attractive?

### 2. Specific environmental risks associated with changes in habitat characteristics

***Individual sites versus wetland complexes***. Much of the
conservation planning for shorebirds has focused on individual wetlands
that play key roles as shorebird staging or wintering locations. In some
key instances, however, shorebirds are not focusing on a single site as
a staging area, but rather are using a complex of sites, shifting
between them as conditions change within or between years. A good
example is the prairie pothole region, where annual rainfall conditions
make a big difference in what wetlands will provide suitable shorebird
habitats. Research is needed to better understand how shorebirds use
habitats such as potholes under different conditions.

***Physical characteristics.*** The characteristics of migration
stopover areas also affect habitat availability and habitat use in ways
that are not well understood. For example, the penetrability of
substrates evidently has an important effect on shorebird foraging, but
is poorly understood. Other important physical factors include shoreline
development and the physiognomic shape of a bay or estuary and effects
on amounts and quality of intertidal habitat, on sediment grain size,
and on food chain relationships. Physical characteristics also will
affect lengths of time that habitats are available to foraging
shorebirds. Research is needed to better understand how intertidal
acreage, shoreline development, degree of tidal flux, and other physical
characteristics of bays and estuaries affect shorebird habitat needs
during migration as well as winter seasons.

In nonmarine wetlands there are whole complexes of research issues
revolving around shorebird habitat requirements and management
activities that should be researched. Little is known of optimal
strategies possible with different management scenarios, or of risks
that may exist with respect to disease, obnoxious vegetation growth, or
trade-offs with benefits to other biota. These issues are further
discussed elsewhere.

There also is growing evidence, but little research, to suggest that the
presence and relative location of suitable resting areas may be an
important habitat attribute of shorebird stopover sites. Research is
needed to better understand this.

Vegetative surroundings (for example forest) of otherwise suitable
wetlands, bays and estuaries affect their suitability to shorebirds,
evidently because shorebirds avoid conditions where stealth approaches
by raptors are easily accomplished (Cresswell & Whitfield, 1994).
Research is needed to understand details of these habitat relationships.

Finally, it seems inherently obvious that the density of available food
will affect habitat suitability for shorebirds at migration stopovers,
but there has been little research to understand where thresholds lie.

# 5) Management Research

Management for species rated as conservation priorities should be a
national priority where the research involves carefully controlled
experiments and has broad applicability, i.e. it is not primarily of
value at single sites unless that site is of overwhelming importance to
a large number of individuals or high priority species.

## A. Assessment of population limiting factors

This heading includes research to determine the relative effects of
population limiting factors, e.g. studying predator behavior,
contaminant ecology, or invertebrate ecology, which may contribute more
to removing limitations to shorebirds than studying shorebird species.
This area of research is very broad, so no detailed examples are
provided. However, the working group determined that research to assess
and manage population limiting factors should be among the highest
priorities for shorebird research.

## B. Research to design techniques for reducing specific population limiting factors

Research designed to reduce population limiting factors (not simply use
factors), e.g. reduction of predation, reduction of contaminant
exposure, increase in prey availability.

### 1. Management techniques to protect nesting shorebirds (Todd Mabee)

Nest predation is a pervasive problem for breeding shorebirds throughout
North America. The loss or alteration of breeding habitat due to
urbanization and agricultural development has been compounded by the
influx of predator communities associated with these altered landscapes.
The changes in the composition or abundance of predators in these
communities may be responsible for decreased recruitment of many
shorebird populations (Helmers and Gratto-Trevor 1996). For example,
high predation rates in coastal habitats have been attributed to
increased predator populations due to alternate food sources (e.g.
landfills) near human population centers (Howe 1982, Haig 1992).

Several methods have been used to reduce nest predation, primarily by
excluding predators from nests or nesting areas rather than removing
predators (i.e. predator control). One common technique used to reduce
nest predation is to place predator exclosures consisting of wire mesh
around nests. Predator exclosures of various sizes and shapes have been
used to protect threatened or endangered species such as Piping Plover
(*Charadrius melodus*) nests on the Atlantic Coast, Great Lakes, and in
the Midwest U.S. (Rimmer and Deblinger 1990, Powell and Cuthbert 1992,
Melvin et al. 1992, Mabee 1996, C. Kruse, unpubl. data.) and Snowy
Plover (*C. alexandrinus*) nests in California and Oregon (Page et al.
1995, M. Stern, unpubl. data), Colorado (Mabee 1996) and in Europe
(Tucker and Heath 1994). At these locations, predator exclosures were
designed to protect nests from the primary nest predators including red
foxes (*Vulpes vulpes*), striped skunks (*Mephitis mephitis*), raccoons
(*Procyon lotor*), gulls (*Larus* spp.), and crows (*Corvus* spp.).
Predator exclosures have also been used to protect nests of common
species such as Killdeer (*C. vociferus*) (Nol and Brooks 1982) and
Pectoral Sandpipers (*Calidris melanotos*) (Estelle et al. 1996) for
research purposes. Lastly, electric fences have been used to reduce
mammalian predation on Piping Plover nests and chicks (Mayer and Ryan
1991).

Although most studies suggest that barrier techniques (i.e. predator
exclosures, electric fencing) increase nest success (Table 6, Deblinger
et al. 1992; but see Nol and Brooks 1982, Mabee 1996), they are
generally not designed to quantify the degree of effectiveness. Future
research on barrier techniques is necessary, and could be strengthened
by 1) identifying which predators are causing nest failure at each
breeding location (to ensure an appropriate barrier design) and 2) using
an appropriate experimental design to quantify the difference in nesting
success between protected and unprotected nests or nesting areas. Then
managers can decide if barrier techniques increase nest success
sufficiently to warrant the expenditure of limited time and resources,
or if alternative options (e.g. eliminating cattle or human disturbances
from nesting areas) may yield better results.

TABLE 6. Observed nest success (%, n) and barrier efficacy of Piping
Plover, Snowy Plover, Killdeer, and Pectoral Sandpiper nests protected
(P) and unprotected (U) by individual predator exclosures or electric
fencing.

+---------+-----+----+----+-----------------+-----------------------+
|         |     | Ne |    | #               |                       |
|         |     | st |    |                 |                       |
|         |     | s  |    |                 |                       |
|         |     | uc |    |                 |                       |
|         |     | ce |    |                 |                       |
|         |     | ss |    |                 |                       |
+=========+=====+====+====+=================+=======================+
| Species | B   | \  | \  | Barrier         | Author                |
|         | arr | (P | (U | efficacy        |                       |
|         | ier | \) | \) |                 |                       |
+---------+-----+----+----+-----------------+-----------------------+
| Piping  |     |    |    | #               |                       |
| Plover  |     |    |    |                 |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 92 | 25 | effective       | Rimmer & Deblinger    |
|         | los | (2 | (2 | against         | 1990                  |
|         | ure | 6) | 4) | medium-sized    |                       |
|         |     |    |    | mammals & birds |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 90 | 17 | effective       | Melvin et al. 1992    |
|         | los | (2 | (2 | against         |                       |
|         | ure | 9) | 4) | medium-sized    |                       |
|         |     |    |    | mammals & birds |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 60 | 75 | ineffective     | Mabee 1996            |
|         | los | (  | (  | against rodents |                       |
|         | ure | 5) | 4) | & snakes        |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | fe  | \  | \  | effective       | Mayer & Ryan 1991     |
|         | nce | -\ | -\ | against some    |                       |
|         |     | -- | -- | mammalian       |                       |
|         |     |    |    | predators       |                       |
+---------+-----+----+----+-----------------+-----------------------+
| Snowy   |     |    |    |                 |                       |
| Plover  |     |    |    |                 |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 69 | 57 | ineffective     | Mabee 1996            |
|         | los | (1 | (1 | against rodents |                       |
|         | ure | 3) | 4) | & snakes        |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 57 | 54 | ineffective     | Mabee 1996            |
|         | los | (1 | (1 | against rodents |                       |
|         | ure | 4) | 3) | & snakes        |                       |
+---------+-----+----+----+-----------------+-----------------------+
| K       |     |    |    |                 |                       |
| illdeer |     |    |    |                 |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 33 | 29 | effective for   | Nol & Brooks 1982     |
|         | los | (1 | (1 | gulls, not      |                       |
|         | ure | 2) | 7) | mammals         |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 14 | 33 | ineffective     | Mabee 1996            |
|         | los | (  | (  | against rodents |                       |
|         | ure | 7) | 9) | & snakes        |                       |
+---------+-----+----+----+-----------------+-----------------------+
| P       |     |    |    |                 |                       |
| ectoral |     |    |    |                 |                       |
| Sa      |     |    |    |                 |                       |
| ndpiper |     |    |    |                 |                       |
+---------+-----+----+----+-----------------+-----------------------+
|         | exc | 77 | 3  | effective       | Estelle et al. 1996   |
|         | los | (1 | (3 | against arctic  |                       |
|         | ure | 3) | 9) | foxes           |                       |
+---------+-----+----+----+-----------------+-----------------------+

### 2. Evaluating created wetland habitats for migrating shorebirds (David Mizrahi)

The quantity and quality of natural intertidal and freshwater habitats
are declining (Tiner 1984, Dahl 1990) and consequently, shorebird
species dependent on these habitats are in jeopardy (Senner and Howe
1984). Significant population declines have been reported in Piping
Plovers (Haig and Plissner 1993), Sanderlings (Howe et al. 1989, Clarke
et al. 1993), Semipalmated Sandpipers (Clark et al 1993, Morrison et al.
1994), Least Sandpipers (Morrison et al. 1994), Short-billed Dowitchers
(Howe et al. 1989, Morrison et al. 1994), and Whimbrel (Howe et al.
1989). Shorebird populations are at particular risk from habitat
declines along traditional migration routes, when thousands of
individuals of several species can congregate at relatively few suitable
sites. Staging areas such as Copper River Delta in southeastern Alaska,
Grays Harbor in Washington, Delaware Bay along the Atlantic coast, Mono
Lake in eastern California, and Cheyenne Bottoms in central Kansas, are
unique because of their capacity to support hundreds of thousands of
shorebirds during migration (Senner and Howe 1984, Harrington and Perry
1995). Alternative sites of comparable quality may be scarce (Myers et
al. 1987).

A variety of human-made or modified wetlands may provide supplemental
habitats for migrating and wintering shorebirds, and ameliorate the loss
of natural wetlands (Davidson and Evans 1986). Wetlands constructed for
mosquito control (Erwin et al. 1994, Brush et al. 1986), managed as
waterfowl habitat (Weber and Haig 1996, Boettcher et al. 1995), or
created by alterations in agricultural (Colwell 1998, Elphick and Oring
1998, Twedt et al. 1998,) and industrial practices (Warnock and Takekawa
1995, Velasquez 1992, Duffield 1986), can support large numbers of
shorebirds at various times during the annual cycle. Several studies
report that under certain conditions, shorebird use of human-made
habitats can be significantly greater than use of adjacent natural
wetlands (e.g., Elphick and Oring 1998, Weber and Haig 1996, Warnock and
Takekawa 1995, Burger et al. 1982). However, Brush et al. (1986) suggest
that shorebird use of wetlands created for open marsh water management
(OMWM) in Massachusetts was not significantly different than natural
pool habitats.

Although it is clear from these studies that shorebird use of human-made
or modified wetlands is widespread, patterns of use are
species-specific, and dependent on factors, such as water depth,
(Elphick and Oring 1998, Weber and Haig 1996), salinity (Velasquez
1992), and tides (Warnock and Takekawa 1995). The effects of these
factors on the use of altered wetlands by shorebirds seem to be related
to access and availability of food resources. However, we know little
about the types of food shorebirds eat in modified wetlands (but see
Weber and Haig 1997, Rehfisch 1994, Velasquez 1992). Additionally, few
data have been published that address the relative abundance and quality
of food resources in modified wetlands compared with adjacent natural
ones (but see Weber and Haig 1996), or how different factors (e.g.,
water level regimes, salinity) affect prey abundance. Large numbers of
birds might be attracted to areas with suboptimal food resources because
optimal habitats are unavailable or monopolized by competitively
superior individuals (e.g., adults versus juveniles). In this way,
modified wetlands may act as habitat sinks.

Do alternative wetland habitats provide the quantity and quality of food
necessary for shorebirds to successfully complete their annual cycle? To
answer this question we must (1) determine the array and abundance of
food resources available in different types of altered wetlands, (2)
compare these food resources with resources available in natural
wetlands, (3) understand how factors such as water level and salinity
affect food abundance and distribution, (4) understand the link between
diet composition and energetic condition, especially during migration,
and (5) determine if there is differential use of man-made or modified
wetlands by different age groups or sexes. This information is essential
to determining the future role of managed and modified wetlands as
alternative habitat for shorebirds.

  --------------- ---------------------- --------------------------------
  Table 1.                               
  Studies that                           
  the document                           
  relative use of                        
  natural and                            
  various                                
  human-made                             
  wetlands by                            
  shorebirds, or                         
  results of                             
  experiments                            
  that                                   

  test the                               
  effects of                             
  habitat                                
  manipulation on                        
  invertebrate                           
  biomass and                            
  shorebird use.                         

  Author(s)       Type of man-made       Results
                  Wetland                

  Burger et al.   Impoundments, mosquito Impoundments and ditches
  (1982)          control ditches        supported higher numbers of

                                         shorebirds than adjacent natural
                                         marshes. However, species

                                         typically breeding in salt
                                         marshes (Clapper Rail,
                                         Sharp-tailed

                                         Sparrow) were more common in
                                         natural marshes.

  Brush et al.    Open Marsh Water       Although shorebirds numbers
  (1986)          Management (OMWM)      increased initially after
                                         construction

                                         of ponds (spoil deposition),
                                         they eventually decreased to

                                         prealteration levels.

  Davidson and    Unspecified            Shorebirds used peripheral
  Evans (1986)                           human-modified wetlands to
                                         extend

                                         feeding time beyond time
                                         available in natural wetlands,
                                         and for

                                         protection from winds. Site
                                         choice and use (e.g., foraging,

                                         roosting) was species-specific
                                         and varied seasonally.

  Duffield (1986) Urban stormwater       Shorebirds preferred stormwater
                  treatment wetland      control marsh over natural
                  complex                

                                         marshes in wetland complex.
                                         Percentage of open water,

                                         emergent vegetation and water
                                         depth accounted for differences

                                         in marsh use.

  Velasquez       Commercial saltpans    Quality of artificial wetlands
  (1992)                                 dependent on benthic macrofauna

                                         abundance and availability.
                                         Availability determined by
                                         salinity

                                         and water level, respectively.
                                         Shorebirds numbers increased

                                         as water levels were lowered.
                                         Variation attributed to changes

                                         in prey composition.
                                         Species-specific differences in
                                         site use

                                         also related to the effect of
                                         salinity on prey composition.

  Erwin et al.    Open Marsh Water       Shorebirds preferred natural
  (1994)          Management (OMWM)      tidal ponds in summer but

                                         OMWM ponds in autumn. Change in
                                         use patterns not

                                         attributable to changes in
                                         species composition. Preference
                                         of

                                         OMWM ponds greatest at low and
                                         high tides compared with

                                         mid-tides and dependent on pond
                                         size (large \> small).

  Rehfisch (1994) Impoundments           Invertebrate prey biomass
                  constructed for        dominated by Chironomidae.
                  waterbird use          

                                         Major determinants of chironomid
                                         biomass were water depth,

                                         organic content of sediments,
                                         and prey biomass. Shorebirds

                                         consumed only a small portion of
                                         prey biomass because water

                                         depth made prey inaccessible.

  Warnock and     Artificial salt pond   Habitat preferences in
  Takekawa (1995) complex                radio-tagged Western Sandpipers

                                         were complex and dependent on
                                         spatial scale, season, and

                                         tidal cycle.

  Weber and Haig  Waterfowl impoundments Overwintering shorebird
  (1996)                                 frequencies higher in tidal
                                         wetlands

                                         than in impoundments. During
                                         migration this relationship was

                                         reversed. Invertebrate density
                                         during the migration period was

                                         greater in impoundments than in
                                         natural tidal wetlands.

  Elphick and     Flooded rice fields    Flooded rice fields had
  Oring (1998)                           significantly higher shorebird
                                         densities

                                         than unflooded fields. Different
                                         straw manipulations used to

                                         improve stubble decomposition
                                         had little affect on densities.

                                         Water depth was an important
                                         predictor of species occurrence.
  --------------- ---------------------- --------------------------------

# Literature Cited

Alerstam, T., P.H. Enckell. 1979. Unpredictable habitats and evolution
of bird migration. Oikos 33(2): 228-232.

Andres, B. A. and G. A. Falxa. 1995. Black Oystercatcher. In The birds
of North America, No. 155 (A. Poole and F. Gill, eds.). Academy Nat.
Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Baker, A.J. and J.G. Strauch, Jr. 1988. Genetic variation and
differentiation in shorebirds. Proceedings of the 19th International
Ornithological Congress, pp 1639-1645.

Baker, M. C., and A. E. M. Baker. 1972. Niche relationships among six
species of shorebirds on their wintering and breeding ranges. Ecological
monographs 43: 193-212.

Bishop, M.A., and N. Warnock. 1998. Migration of Western Sandpipers:
links between their Alaskan stopover areas and breeding grounds. Wilson
Bull. 110: 457-624.

Blem, C. R. 1990. Avian energy storage, p. 59-113. In D. M. Power
\[ed.\], Current Ornithology. Plenum Press, New York.

Boettcher, D. R., S. M. Haig, and W. C. Bridges. 1995. Habitat-related
factors affecting the distribution of nonbreeding American Avocets in
coastal South Carolina. Condor 97: 68-82.

Brush, T., R. A. Lent, T. Hruby, B. A. Harrington, R. M. Marshall, and
W. G. Montgomery. 1986. Habitat use by salt marsh birds and response to
open marsh water management. Colonial Waterbirds 9: 189-195.

Bto, M.E.M. and Summers, R.W. 1987. Wader populations on the
non-estuarine coasts of Britain and Northern Ireland (UK): Results of
the 1984-85 winter shorebird count: A report to the British Trust for
Ornithology and the Wader Study Group.Bird Study 34(1): 71-81.

Burger, J. 1988. Jamaica Bay (New York, USA) Studies: VIII an overview
of abiotic factors affecting several avian groups. Journal of Coastal
Research 4(2): 193-205.

Burger, J., Shisler, J, and F. H. Lesser. Avian utilization on six salt
marshes in New Jersey. Biological Conservation 23: 187-212.

Burlando, B., A. Arillo, S. Spanò, and M. Machetti. 1996. A study of the
genetic variability in populations of the European Woodcock (Scolopax
rusticola) by random amplification of polymorphic DNA. Italian Journal
of Zoology 63: 31-36.

Butler, R. W., G. W. Kaiser, and G. E. J. Smith. 1987. Migration
chronology, length of stay, sex ratio, and weight of Western Sandpipers
Calidris mauri on the south coast of British Columbia.. J. Field.
Ornithol. 58: 103-111.

Butler, R. W., T. D. Williams, N. Warnock, and M. A. Bishop. 1997. Bird
migration: an obligate requirement for wind-assisted flight? Auk 114:
456-466.

Butler, R. W., and G. W. Kaiser. 1995. Migration chronology, sex ratio,
and body mass of Least Sandpipers in British Columbia. Wilson Bull. 107:
413-422.

Chamberlain, C.P., J.D. Blum, R.T. Holmes, X. Feng, T.W. Sherry, and
G.R. Graves. 1997. The use of isotope tracers for identifying
populations of migratory birds. Oecologia 109: 132-141.

Clark, K. E., L. J. Niles and J. Burger. 1993. Abundance and
distribution of migrant shorebirds in Delaware Bay. Condor 95: 694-705.

Colwell, M. A. and J. R. Jehl, Jr. 1994. Wilson\'s Phalarope. In The
birds of North America, No. 83 (A. Poole and F. Gill, eds.). Academy
Nat. Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Colwell, M.A, J.D. Reynolds, C.L. Gratto, D. Schamel. and D.M. Tracy.
1986. Phalarope philopatry. Acta. Cong. Int. Orn. 19: 585-593

Colwell-Mark-A. 1993. Shorebird community patterns in a seasonally
dynamic estuary. Condor 95(1): 104-114.

Colwell, M. A., & S.L. Dodd. 1997. Environmental and habitat correlates
of pasture use by nonbreeding shorebirds. Condor 99(2): 337-344.

Colwell, M. A., & S.L. Landrum. 1993. Nonrandom shorebird distribution
and fine-scale variation in prey abundance. Condor 95(1): 94-103

Connors, P.G., J.P. Myers, C.S.W. Connors, and F.A. Pitelka. 1981.
Interhabitat movements by Sanderlings in relation to foraging
profitability and the tidal cycle. Auk 98: 49-64.

Cooper, J. M. 1994. Least Sandpiper. In The birds of North America, No.
115 (A. Poole and F. Gill, eds.). Academy Nat. Sci., Philadelphia; Amer.
Ornithol. Union, Washington, D.C.

Cresswell, W. & D.P. Whitfield. 1994. The effects of raptor predation on
wintering wader populations at Tyninghame estuary, southeast Scotland.
Ibis 136: 223-232.

Dahl, T. E. 1990. Wetland losses in the United States 1780\'s to
1980\'s. U. S. Department of Interior, Fish and Wildlife Service,
Washington, D. C.

Davidson, N. C., and P. R. Evans. 1986. The role and potential of
man-made and man-modified wetlands in the enhancement of the survival of
overwintering shorebirds. Colonial Waterbirds 9: 176-188.

Day, J. H., and M. A. Colwell. 1998. Waterbird communities in rice
fields subjected to different post-harvest treatments. Colonial
Waterbirds 21: 185-197.

Deblinger, R. D., J. J. Vaske, and D. W. Rimmer. 1992. An evaluation of
different predator exclosures used to protect Atlantic Coast Piping
Plover nests. Wildl. Soc. Bull. 20: 274--279.

Duffield, J. M. 1986. Waterbird use of an urban stormwater wetland
system in central California. Colonial Waterbirds 9: 227-235.

Duffy, D. C., N. Atkins, and D. C. Schneider. 1981. Do shorebirds
compete on their wintering grounds? Auk 98: 215-229.

Dunn, P. O., T. A. May, M. A. McCollough, and M. A. Howe. 1988. Length
of stay and fat content of migrant Semipalmated Sandpipers in eastern
Maine. Condor 90: 824-835.

Elphick, C. S., and L. W. Oring. 1998. Winter management of California
rice fields for waterbirds. J. Appl. Ecol. 35: 95-108.

Elphick, C. S., and T. L. Tibbitts. 1998. Greater Yellowlegs. In The
birds of North America, No. 355 (A. Poole and F. Gill, eds.). Academy
Nat. Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Engilis, A.,Jr {a}, L.W. Oring, E. Carrera, J.W. Nelson, & A.
Martinez-Lopez. 1998. Shorebird surveys in Ensenada Pabellones and Bahia
Santa Maria, Sinaloa, Mexico: Critical winter habitats for Pacific
flyway shorebirds. Wilson Bull. 110(3): 332-341.

Erwin, R. M., J. S. Hatfield, M. A. Howe, and S. S. Klugman. 1994.
Waterbird use of saltmarsh wetlands created for open marsh water
management. J. Wildl. Manage. 58: 516-524.

Estelle, V. B., T. J. Mabee, and A. H. Farmer. 1996. Effectiveness of
predator exclosures for Pectoral Sandpiper nests in Alaska. J. Field
Ornithol. 67: 447-452.

Evans, P. R., and M. W. Pienkowski. 1984. Population dynamics of
shorebirds. Pp. 83-123 in Shorebirds: Breeding behavior and populations
(J. Burger and B. L. Olla, eds.). Plenum Press, NY.

Farmer, A.H., and A.H. Parent. 1997. Effects of the landscape on
shorebird movements at spring migration stopovers. Condor 99: 698-707.

Figuerola, J., and A. Bertolero. 1998. Sex differences in the stopover
ecology of Curlew Sandpipers Calidris ferruginea at a refuelling area
during spring migration. Bird Study 45: 313-319.

Gill, R. E., Jr., P. Canevari, and E. H. Iverson. 1998. Eskimo Curlew.
In The birds of North America, No. 347 (A. Poole and F. Gill, eds.).
Acad. Nat. Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Girardo-O. 1992. Wader migration in continental France: Synthesis of the
literature. Alauda 60(1): 13-33.

Gratto, C.L., R.I.G. Morrison, and F. Cooke. 1985. Philopatry, site
tenacity, and mate fidelity in the Semipalmated Sandpiper. Auk 102:
16-24.

Gratto-Trevor, C. L. 1997. Climate change: proposed effects on shorebird
habitat, prey, and numbers in the outer Mackenzie Delta. Pp. 205-210 in
Mackenzie Basin Impact Study Final Report (S. J. Cohen, ed.).
Atmospheric Environment Science, Environment Canada, Downsview, Ont.

Gratto-Trevor, C. L. 1992. Semipalmated Sandpiper. In The birds of North
America, No. 6 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Green, G. H., J. J. D. Greenwood, and C. S. Lloyd. 1977. The influence
of snow conditions on the date of breeding of wading birds in north-east
Greenland. J. Zool. 183: 311-328.

Haig, S. M. 1992. Piping Plover. In The birds of North America, No. 2
(A. Poole and F. Gill, eds.). Academy Nat. Sci., Philadelphia; Amer.
Ornithol. Union, Washington, D.C.

Haig, S. M., and L. W. Oring. 1988. Mate, site, and territory fidelity
in Piping Plovers. Auk 105: 268-277.

Haig, S.M. and L.W. Oring. 1988. Genetic differentiation of Piping
Plovers across North America. Auk 105: 260-267.

Haig, S.M., C.L. Gratto-Trevor, T.D. Mullins, and M.A. Colwell. 1997.
Population identification of western hemisphere shorebirds throughout
the annual cycle. Molecular Ecol. 6: 203-211.

Haig, S.M., D.W. Mehlman, and L.W. Oring. 1998. Avian movements and
wetland connectivity in landscape conservation. Conservation Biol. 12:
749-758.

Haig, S.M., and L.W. Oring. 1988a. Mate, site, and territory fidelity in
Piping Plovers. Auk 105: 268-277.

Haig, S.M., and L.W. Oring. 1988b. Distribution and dispersal in the
Piping Plover. Auk 105: 630-638.

Haig, S. M., C.L. Gratto-Trevor, T.D. Mullins, & M.A. Colwell. 1997.
Population identification of Western Hemisphere shorebirds throughout
the annual cycle. Molecular Ecol. 6(5): 413-427.

Harrington, B. A., F. J. Leeuwenberg, S. Lara-Resende, R. McNeil, et al.
1991. Migration and mass change of White-rumped Sandpipers in North and
South America. Wilson Bull. 104: 621-636.

Harrington, B. A., and E. Perry. 1995. Important shorebird staging sites
meeting Western Hemisphere Shorebird Reserve Network criteria in the
United States. U. S. Department of Interior, Fish and Wildlife Service,
Washington, D. C.

Hayes, F. E., S. M. Goodman, J. A. Fox, T. Granizo T., & N. E. L¢pez.
1990. North American bird migrants in Paraguay. Condor 92: 947-960.

Helmers, D. L. and C. L. Gratto-Trevor. 1996. Effects of predation on
migratory shorebird recruitment. Trans. N. Am. Wildl. Nat. Resour. Conf.
61: 50-61.

Hicklin, P. W. 1987. The migration of shorebirds in the Bay of Fundy.
Wilson Bull. 99: 540-570.

Hitchcock, C. L., and C. L. Gratto-Trevor. 1997. Diagnosing a shorebird
local population decline with a stage-structured population model.
Ecology 78: 522-534.

Holmes, R. T. 1971. Density, habitat, and the mating system of the
Western Sandpiper (Calidris mauri). Oecologia 7: 191-208.

Holmes, R. T. 1972. Ecological factors influencing the breeding season
schedule of Western Sandpipers (Calidris mauri) in subarctic Alaska. Am.
Midl. Nat. 87: 472-491.

Holmes, R. T., and F. A. Pitelka. 1998. Pectoral Sandpiper. In The birds
of North America, No. 348 (A. Poole and F. Gill, eds.). Academy Nat.
Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Holmgren, N., H. Ellegren, and J. Pettersson. 1993. Stopover length,
body mass and fuel deposition rate in autumn migrating Dunlins Calidris
alpina: evaluating the effects of moulting status and age. Ardea 81:
9-20.

Howe, M. A. 1982. Social organization in a nesting population of eastern
Willets (Catoptrophorus semipalmatus). Auk 99: 88-102.

Howe, M. A., P. H. Geissler, and B. A. Harrington. 1989. Population
trends of North American shorebirds based on the International Shorebird
Survey. Biological Conservation 49: 185-199.

Iverson, G.C., S.E. Warnock, R.W. Butler, M.A. Bishop, and N. Warnock.
1996. Spring migration of Western Sandpipers along the Pacific coast of
North America: a telemetry study. Condor 98: 10-21.

Iverson, G. C., S.E. Warnock, R.W. Butler, M.A. Bishop, & N. Warnock.
1996. Spring migration of western sandpipers along the Pacific Coast of
North America: A telemetry study. Condor 98 (1): 10-21.

Johnson, O. W., and P. G. Connors. 1996. American Golden-Plover. In The
birds of North America, No. 201 (A. Poole and F. Gill, eds.). Academy
Nat. Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Jönsson, P. E. 1991. Reproduction and survival in a declining population
of the southern Dunlin Calidris alpina schinzii. Wader Study Group Bull.
61: 56-68.

Keijl, G. O., M. W. J. van Roomen, P. S. Ruiters, and A. Wijker. 1992.
Migration of waders and other waterbirds along the Mediterranean coast
of Israel, spring 1989. Werkgroep Internationaal Wad- en Watervogel
Onderzoek-report 30. Zeist, The Netherlands.

Keppie, D. M., and R. M. Whiting, Jr. 1994. In The birds of North
America, No. 100 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Klima, J., and J. R. Jehl, Jr. 1998. Stilt Sandpiper. In The birds of
North America, No. 341 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Knopf, F. L. 1996. Mountain Plover. In The birds of North America, No.
211 (A. Poole and F. Gill, eds.). Academy Nat. Sci., Philadelphia; Amer.
Ornithol. Union, Washington, D.C.

Knopf, F.L., and J.R. Rupert. 1996. Reproduction and movements of
Mountain Plovers breeding in Colorado. Wilson Bull. 108: 28-35.

Lanctot, R. B., and C. D. Laredo. Buff-breasted Sandpiper. In The birds
of North America, No. 91 (A. Poole and F. Gill, eds.). Academy Nat.
Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Lank, D. B. 1983. Migratory behavior of Semipalmated Sandpipers at
inland and coastal staging areas. Ph.D. diss. Cornell University.
Ithaca, NY.

Lappo, E. G. 1996. Comparisons of breeding range structure for Dunlin
Calidris alpina and Curlew Sandpiper Calidris ferruginea: conservative
and nomadic tundra waders. Wader Study Group Bulletin 80: 41-46.

Laredo, C. D. 1996. Observations on migratory and resident shorebirds in
lakes in the highlands of north-western Argentina. International Wader
Studies 8: 103-111.

Lester, R. T., and J. P. Myers. 1991. Double jeopardy for migrating
wildlife. Pp 119-133 in Global climate change and life on earth (R. L.
Wyman, ed.). Chapman and Hall, NY.

Lyons, J. E., and S. M. Haig. 1995. Fat content and stopover ecology of
spring migrant Semipalmated Sandpipers in South Carolina. Condor 97:
427-437.

Mabee, T. J. 1996. Nesting ecology of Piping Plovers, Snowy Plovers, and
Killdeer in Southeastern Colorado. M. S. thesis, Colorado State Univ.,
Fort Collins, Colorado.

MacLean, S. F., Jr. 1969. Ecological determinants of species diversity
of Arctic sandpipers near Barrow, Alaska. Ph.D. diss., Univ. California,
Berkeley, CA.

Mayer, P. M. and M. R. Ryan. 1991. Electric fences reduce mammalian
predation on

Melvin, S. M., L. H. MacIvor, and C. R. Griffin. 1992. Predator
exclosures: a

Miller, E. H. 1983. Habitat and breeding cycle of the Least Sandpiper
(Calidris minutilla) on Sable Island, Nova Scotia. Can. J. Zool. 61:
2880-2898.

Morrison, R. I. G. 1984. Migration systems of some New World shorebirds.
In Shorebirds: migration and foraging behavior, pp 125-202, J. Burger
and B. Olla, eds. Plenum Press, N. Y.

Morrison, R. I. G., C. Downes, and B. Collins. 1994. Population trends
of shorebirds on fall migration in eastern Canada 1974-1991. Wilson
Bull. 106: 431-447.

Morrison, R. I. G., and B. A. Harrington. 1979. Critical shorebird
resources in James Bay and eastern North America.. Trans. of the 44th
No. Am. Wildl. and Nat. Res. Conf., Wildl. Management Inst., Wash., D.
C.

Morrison, R.I.G., R.K. Ross, J. Guzman, and A. Estrada. 1993. Aerial
surveys of Nearctic shorebirds wintering in Mexico: Preliminary results
of surveys on the Gulf of Mexico and Caribbean coasts. Can. Wildl.
Serv., Prog. Notes 206: 1-14.

Morrison, R. I. G. 1997. The use of remote sensing to evaluate shorebird
habitats and populations on Prince Charles Island, Foxe Basin, Canada.
Arctic 50 (1): 55-75.

Moskoff, W. 1995. Solitary Sandpiper. In The birds of North America, No.
156 (A. Poole and F. Gill, eds.). Academy Nat. Sci., Philadelphia; Amer.
Ornithol. Union, Washington, D.C.

Muenster. OAG. 1988. Goals and first results of the International Wader
Counts: Inland migration of waders. VOGELWELT 109(1): 3-25 (in German).

Myers P. J., R. I. G. Morrison, P. Z. Antas, B. A. Harrington, T. E.
Lovejoy, M. Sallaberry, S. E. Senner and A. Tarak. 1987. Conservation
strategy for migratory species. American. Scientist 75: 19-26.

Myers, J.P. 1981. Cross-seasonal interactions in the evolution of
sandpiper social systems. Behavioral Ecol. and Sociobiol. 8: 195-202.

Myers, J.P., C.T. Schick, and G. Castro. 1988. Structure in Sanderling
(Calidris alba) populations:the magnitude of intra- and interyear
dispersal during the nonbreeding season. Pages 604-615 in Acta XIX
Congressus Internationalis Ornithologici. University of Ottawa Press,
Ottawa.

Myers-J-P. 1981. A test of 3 hypotheses for latitudinal segregation of
the sexes in wintering birds. Canadian J. Zoology 59(8): 1527-1534.

Newton, I, & L.C. Dale. 1997. Effects of seasonal migration on the
latitudinal distribution of west Palaearctic bird species.
J.-of-Biogeography 24 (6): 781-789.

Nol, E. and R. J. Brooks. 1982. Effects of predator exclosures on
nesting success of Killdeer. J. Field Ornithol. 53: 263-268.

Nol, E., Blanken, M.S., Flynn, L. 1997. Sources of variation in clutch
size, egg size and clutch completion dates of semipalmated plovers in
Churchill, Manitoba. Condor, 99: 389-396.

Nol, E., M. Sullivan Blanken, & L. Flynn. 1997. Sources of variation in
clutch size, egg size and clutch completion dates of Semipalmated
Plovers in Churchill Manitoba. Condor 99: 389-396.

Nol, E., and R. C. Humphrey. 1994. American Oystercatcher. In The birds
of North America, No. 82 (A. Poole and F. Gill, eds.). Academy Nat.
Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Oring, L. W., E. M. Gray, and J. M. Reed. 1997. Spotted Sandpiper. In
The birds of North America, No. 289 (A. Poole and F. Gill, eds.).
Academy Nat. Sci., Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Oring, L. W., and D. B. Lank. 1986. Polyandry in Spotted Sandpipers: the
impact of environment and experience, p. 21-42. In D. Rubenstein and P.
Wrangham \[eds.\], Ecological aspects of social evolution. Princeton
Univ. Press, Princeton, NJ.

Oring, L.W., J. M. Reed, and J.A.R. Alberico. 1994. Mate acquisition
tactics in polyandrous Spotted Sandpipers (Actitis macularia): the role
of age and experience. Behavioral Ecol. 5: 9-16.

Oring, L.W., and D.B. Lank. 1984. Breeding area fidelity, natal
philopatry, and the social systems of sandpipers. Pages 125-147 in J.
Burger and B. L. Olla, editors. Shorebirds: breeding behavior and
populations. Plenum Press, New York.

Page, G. W., J. S. Warriner, J. C. Warriner, and P. W. C. Paton. 1995.
Snowy Plover. In The birds of North America, No. 154 (A. Poole and F.
Gill, eds.). Academy Nat. Sci., Philadelphia; Amer. Ornithol. Union,
Washington, D.C.

Page, G. and A. L. A. Middleton. 1972. Fat deposition during autumn
migration in the semipalmated sandpiper. Bird Banding 43: 85-96.

Page,G. W., Palacios, E, Alfaro-Lucia, G.S., Stenzel, L.E., Jungers, M.
1997. Numbers of wintering shorebirds in coastal wetlands of Baja
California, Mexico. J.-of-Field-Ornithology. Autumn 68(4): 562-574.

Parmelee, D. F. 1992. White-rumped Sandpiper. In The birds of North
America, No. 29 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Parmelee, D. F., D. W. Greiner, and W. D. Graul. 1968. Summer schedule
and breeding biology of the White-rumped Sandpiper in the central
Canadian Arctic. Wilson Bull. 80: 5-29.

Paton, P.W.C. 1995. Breeding biology of Snowy Plovers at Great Salt
Lake, Utah. Wilson Bull. 107: 275-288.

Paton, P.W.C., and T.C. Edwards, Jr. 1996. Factors affecting interannual
movements of Snowy Plovers. Auk 113: 534-543.

Paulson, D. S. 1995. In The birds of North America, No. 186 (A. Poole
and F. Gill, eds.). Academy Nat. Sci., Philadelphia; Amer. Ornithol.
Union, Washington, D.C.

Pfister, C., M. J. Kasprzyk, and B. A. Harrington. 1998. Body fat levels
and annual return in migrating Semipalmated Sandpipers. Auk 115:
904-915.

Pfister, C., B.A. Harrington, & M.A. Levine. 1992. The impact of human
disturbance on shorebirds at a migration staging area. Biological
Conservation 60(2): 115-126.

Piersma, T., J. Van-Gils, P. DeGoeij, & J. Van-Der-Meer. 1995.
Holling\'s functional response model as a tool to link the food-finding
mechanism of a probing shorebird with its spatial distribution. J. Anim.
Ecol. 64(4): 493-504.

Pitelka, F. A., R. T. Holmes, and S. F. MacLean, Jr. 1974. Ecology and
evolution of social organization in arctic sandpipers. Amer. Zool. 14:
185-204.

Plissner (a), J.H., S.M. Haig, and L.W. Oring. Post-breeding movements
among American Avocets and wetland connectivity in the U.S. western
Great Basin. Auk (in review).

Plissner (b), J.H., S.M. Haig, and L.W. Oring. Within and among year
movements of American avocets in the Western Great Basin. Wilson Bull.
(in press).

Plissner (c), J.H., L.W. Oring, and S.M. Haig. Space use among Killdeer
in Great Basin wetlands. J. Wildl. Manage.(in review).

Post, W. and M. M. Browne. 1976. Length of stay and weights of inland
migrating shorebirds. Bird Banding 47: 333-339.

Powell, A. N. and F. J. Cuthbert. 1992. Habitat and reproductive success
of Piping Plovers nesting on Great Lakes islands. Wilson Bull. 104:
155-161.

Rabinowitz, D. 1981. Seven forms of rarity. In The biological aspects of
rare plant conservation. (ed. H. Synge). Pp. 205-217. J. Wiley & Sons,
New York, New York.

Reed, J.M., R.C. Fleischer, J. Eberhard, and L. W. Oring. 1996.
Minisatellite DNA variability in two populations of Spotted Sandpipers
Actitis macularia in Minnesota, U.S.A. Wader Study Group Bulletin 79:
115-117.

Reed, J.M., and L.W. Oring. 1992. Reconnaissance for future breeding
sites by Spotted Sandpipers. Behavioral Ecol. 3: 310-317.

Reed, J.M., and L.W. Oring. 1993. Philopatry, site fidelity, dispersal,
and survival of Spotted Sandpipers. Auk 110: 541-551.

Rehfisch, M. M. 1994. Man-made lagoons and how their attractiveness to
waders might be increase by manipulating the biomass of an insect
benthos. J. Applied Ecol. 31: 383-401.

Rimmer, D. W. and R. D. Deblinger. 1990. Use of predator exclosures to
protect Piping Plover nests. J. Field Ornithol. 61: 217-233.

Robinson, J. A., & L. W. Oring. 1996. Long-distance movements by
American Avocets and Black-necked Stilts.. J. Field Ornithol. 67:
307-320.

Robinson, J. A., L. W. Oring, J. S. Skorupa, and R. Boettcher. 1997.
American Avocet. In The birds of North America, No. 275 (A. Poole and F.
Gill, eds.). Academy Nat. Sci., Philadelphia; Amer. Ornithol. Union,
Washington, D.C.

Robinson, J.A., and L.W. Oring. 1997. Natal and breeding dispersal in
American Avocets. Auk 114: 416-430.

Safran, R.J., Isola, C.R., Colwell, M.A., Williams, O.E. 1997. Benthic
invertebrates at foraging locations of nine waterbird species in managed
wetlands of the northern San Joaquin Valley, California. Wetlands, 17:
407-415.

Sandercock, B. K., and C. L. Gratto-Trevor. 1997. Local survival in
Semipalmated Sandpipers Calidris pusilla breeding at La Perouse Bay,
Canada. Ibis 139: 305-312.

Schneider, D. C., and B. A. Harrington. 1981. Timing of shorebird
migration in relation to prey depletion. Auk 98: 801-811.

Senner, S. E., and B. J. McCaffrey. 1997. Surfbird. In The birds of
North America, No. 266 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Senner, S. E., and M. A. Howe. 1984. Conservation of nearctic
shorebirds. Pages 329-421 in Behavior of marine animals, Vol. 5. (J.
Burger and B. L. Olla, eds.). Plenum Press, New York.

Senner,S. E, G.C. West, & D.W. Norton. 1981. The spring migration of
western sandpipers (Calidris mauri) and dunlins (Calidris alpina
pacifica) in southcentral Alaska, USA: Numbers, timing and sex ratios.
J. Field Ornithol. 52(4): 271-284.

Shuford, W. D., G.W. Page,& J.E. Kjelmyr. 1998. Patterns and dynamics of
shorebird use of California\'s central valley. Condor 100(2): 227-244.

Skagen, S. K. 1997. Stopover ecology of transitory populations: the case
of migrant shorebirds. Ecol. Studies 125: 244-269.

Skagen, S. K. and F. L. Knopf. 1994. Migrating Shorebirds and habitat
dynamics at a prairie wetland complex. Wilson Bull. 106(1): 91-105.

Skagen, S. K., and F. L. Knopf. 1994. Residency patterns of migrating
sandpipers at a midcontinental stopover. Condor 96: 949-958.

Skagen, S.K., Oman, H.D. 1996. Dietary flexibility of shorebirds in the
western hemisphere. Canadian Field - Naturalist 110: 419-444.

Skagen, S.K., and F.L. Knopf. 1993. Toward conservation of
midcontinental shorebird migrations. Conservation Biology 7: 533-541.

Skagen, S.K., and F.L. Knopf. 1994. Migrating shorebirds and habitat
dynamics at a prairie wetland complex. Wilson Bull. 106:91-105.

Skeel, M. A., and E. P. Mallory. 1996. Whimbrel. In The birds of North
America, No. 219 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Stenzel, L.E., J.C. Warriner, J.S. Warriner, K.S. Wilson, F.C. Bidstrup,
and G.W. Page. 1994. Long-distance breeding dispersal of Snowy Plovers
in western North America. J. Animal Ecol. 63: 887-902.

Summers, R. W., and L. G. Underhill. 1987. Factors related to breeding
production of Brent Geese Branta b. bericla and waders (Charadrii) on
the Taimyr Peninsula. Bird Study 34: 161-171.

Sutherland, W. J. 1988. Predation may link the cycles of lemmings and
birds. Trends Ecol. and Evol. 5: 29-30.

Thompson, P. S., D. Baines., J. C. Coulson, and G. Longrigg. 1994. Age
at first breeding, philopatry, and breeding site-fidelity in the Lapwing
Vanellus vanellus. Ibis 136: 474-484.

Thompson, J. J. 1993. Modelling the local abundance of shorebirds
staging on migration. Theoretical-Population-Biology. 44 (3): 299-315.

Tiner, R. W. 1984. Wetlands of the United States: Current status and
trends. U. S. Fish and Wildlife Service, Washington, D. C.

Treuren, R.V., R. Bijlsma, J.M. Tinbergen, D. Heg, and L.Van de Zande.
Submitted. Analysis of population structure and estimates of gene flow
in the oystercatcher (Haematopus ostralegus) using microsatellites.
Molecular Ecol. .

Tucker, G. M. and Heath, M. F. 1994. Birds in Europe: their conservation
status. Cambridge, U. K.: Birdlife International (Birdlife Conservation
Series no. 3).

Twedt, D. J., C. O. Nelms, V. E. Rettig, and S. R. Aycock. Shorebird use
of managed wetlands in the Mississippi Alluvial Valley. American Midland
Naturalist 140: 140-152.

Van-Der-Have, T., & V. Van-Den-Berk. 1994. The Mediterranean migration
route: Network of wetlands for waterbirds. Limosa. 67 (4): 159-162.

Velasquez, R. 1992. Managing artificial saltpans as a waterbird habitat:
Species\' responses to water level manipulation. Colonial Waterbirds 15:
43-55.

Warnock, N. D., and R. E. Gill. 1996. Dunlin. In The birds of North
America, No. 203 (A. Poole and F. Gill, eds.). Academy Nat. Sci.,
Philadelphia; Amer. Ornithol. Union, Washington, D.C.

Warnock, N., G.W. Page, and B. K. Sandercock. 1999. Local survival of
Dunlin wintering in California. Condor 100: 906-915.

Warnock, N., G.W. Page, and L.E. Stenzel. 1995. Non-migratory movements
of Dunlins on their California wintering grounds. Wilson Bull. 107:
131-139.

Warnock, N., S. M. Haig, and L. W. Oring. 1998. Monitoring species
richness and abundance of shorebirds in the western Great Basin. Condor
100: 589-600.

Warnock, N., and M. A. Bishop. 1998. Spring stopover ecology of migrant
Western Sandpipers. Condor 100: 456-467.

Warnock, S. E., and J. Y. Takekawa. Habitat preferences of wintering
shorebirds in a temporally changing environment. Auk 112: 920-930.

Warnock, S.W., and J.Y. Takekawa. 1996. Wintering site fidelity and
movement patterns of Western Sandpipers Calidris mauri in the San
Francisco Bay estuary. Ibis 138: 160-167.

Weber, L. M., and S. M. Haig. 1996. Shorebird use of South Carolina
managed and natural coastal wetlands. J. Wildl. Manage.60: 73-82.

Weber, L. M., and S. M. Haig. 1997. Shorebird diet and size selection of
nereid polychaete in South Carolina coastal diked wetlands. J. Field
Ornithol. 68: 358-366.

Wenink, P.W., A.J. Baker, H-U. Rösner, and M.G.J. Tilanus. 1996. Global
mitochondrial DNA phylogeography of Holarctic breeding Dunlins (Calidris
alpina). Evolution 50: 318-330.

Wenink, P.W., A.J. Baker, and M.G.J. Tilanus. 1994. Mitochondrial
control-region sequences in two shorebird species, the Turnstone and the
Dunlin, and their utility in population genetic studies. Molecular
Biology and Evolution 11 :22-31

Whitfield, D. P. 1985. Raptor predation on wintering waders in southeast
Scotland. Ibis 127: 544-558.

Wilson, W. H., Jr. 1989. Predation and the mediation of intraspecific
competition in an infaunal community in the Bay of Fundy. J. Exp. Mar.
Biol. Ecol. 132: 221-245.