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| ISBN-13: | 9780520947962 |
|---|---|
| Publisher: | University of California Press |
| Publication date: | 11/16/2010 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 344 |
| File size: | 4 MB |
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Shorebird Ecology, Conservation, and Management
By Mark A. Colwell
UNIVERSITY OF CALIFORNIA PRESS
Copyright © 2010 the Regents of the University of CaliforniaAll rights reserved.
ISBN: 978-0-520-94796-2
CHAPTER 1
Introduction
CONTENTS
Diversity and Distribution
Varied Ecomorphology
Diverse Social Systems
Globe-Trotting Migrants
Wetland Dependence
Conservation and Management
Rationale for and Organization of This Book
WHY STUDY SHOREBIRDS? I've occasionally asked myself this question over the 30 years that I've been an avian ecologist. At first blush, the answer may not be that scientific: because they're fascinating! However, the fascination and wonder of shorebirds (or waders as they're known elsewhere in the English-speaking world) stems from a diversity that seems unrivaled by other bird groups. This diversity is evident across scientific disciplines as varied as biogeography, bioenergetics, behavioral ecology, and evolutionary biology. An additional advantage is that, for the most part, shorebirds provide abundant viewing opportunities in a variety of ecological settings. This makes for relatively easy study by scientists and birders alike. Candidly, I suppose that many of the following observations that characterize shorebirds can be applied, with relatively minor changes, to other avian taxa. This portrayal of shorebirds as ideal and wondrous subjects of study is made more relevant by their population status and need for effective management and conservation. Some of the rarest avian species are shorebirds, and even common ones are experiencing population declines. Accordingly, the relevance of applied ecology is immediate and pressing. Still, their attributes make shorebirds especially alluring subjects for study.
DIVERSITY AND DISTRIBUTION
Ornithologists recognize approximately 215 species of shorebird, unevenly distributed among 14 families in the order Charadriiformes (Table 1.1). To some extent, this diversity may be an artificial human construct, because recent molecular studies suggest the group is polyphyletic (van Tuinen et al. 2004). In other words, the various shorebird families come from two distinct evolutionary lineages. These separate origins may explain the contrasting and diverse life histories and distributions of shorebirds. Regardless, the 14 shorebird families consist of four monotypic families (that is, consisting of a single species) that have restricted breeding distributions and are either nonmigratory (the Plains-wanderer of Australia and the Magellanic Plover of Tierra del Fuego) or undertake relatively short-distance movements between breeding and wintering grounds (Ibisbill and Crab Plover). The most diverse groups, sandpipers and plovers, have broad distributions, spanning hemi spheres. Most sandpipers breed in northern regions, and many migrate to the extremes of southern continents. Most plovers, however, are temperate and tropical species, and they are less prone to move long distances between breeding and wintering areas. It is no surprise that families with fewer species tend to be more restricted in their distributions. However, the oystercatchers, stilts, and avocets are nearly cosmopolitan, being absent from only Antarctica and surrounding islands. By contrast, the sheathbills are permanent residents of Antarctica and sub-Antarctic islands; the seedsnipes reside in higher elevations of the Andes of South America.
Thus, shorebirds are a diverse group. At least one recent discovery of a previously undescribed woodcock (Bukidnon Woodcock: Kennedy et al. 2001) and the rediscovery of a plover from Southeast Asia (White-faced Plover: Kennerley et al. 2008) have increased the diversity of the group. Shorebirds occupy open habitat at the extremes of latitude, and they range from sea level to high elevations. By comparison, waterfowl (375 species) and raptors (313 species) are slightly more speciose than shorebirds, but they are arguably more uniform in their foraging ecologies, social organization, and behaviors.
VARIED ECOMORPHOLOGY
A consequence of cosmopolitan distributions is that closely related shorebirds have evolved in diverse habitats, with consequences for morphological adaptations. Nowhere is this more apparent than in the variation exhibited in body size and feeding apparatus. Among the sandpipers, for instance, mass varies from tiny calidridines (<20 g) to large curlews (>500 g); several other species are much larger (such as stone curlews at >800 g). Most shorebirds meet their daily energy requirements consuming a diet of soft-bodied macroinvertebrates; others consume bivalves, which are ground to a pulp by powerful gizzards. Some larger species, such as thick-knees and curlews, occasionally eat small lizards, fishes, and the eggs of other birds. Pratincoles are insectivorous, feeding on the wing like swallows. Plant material is generally uncommon in the diet of most species, although some Arctic species feed extensively on plant material and fruits late in summer. Recent evidence has shown that some small calidridine sandpipers feeding in intertidal habitats lap "biofilm" with brushlike tongues.
To acquire food, shorebirds have evolved diverse bill morphologies and feeding behaviors. Phalaropes use their needlelike bills to facilitate the movement of water droplets that contain prey through the physics of surface water tension (Rubega and Obst 1993). Other bill shapes include spatulate (Spoon-billed Sandpiper), recurved (avocets), and decurved (curlews); only one bird has a laterally asymmetrical bill (Wrybill). Considerable variation and adaptation in bill morphology even exists within species. For instance, individual Eurasian Oystercatchers have one of three bill shapes, each specialized for feeding on different prey. One type is used to chisel open bivalves, a second slits the adductor muscle to open shells, and a third is better suited for probing into soft substrates for invertebrates (Sutherland et al. 1996).
These diverse bill shapes have been the subject of considerable ecological research, fueled by the supposition that species with similar bill morphologies must experience competition for food. Early on, researchers examined habitat use and aggressive interactions as a means of habitat segregation in dynamic tidal habitats of coastal estuaries (e.g., Recher 1966). More recent analyses of the patterns derived from competition theory have examined mixed species flocks of migrant sandpipers and the minimum size ratio of bills of closely related species (Eldridge and Johnson 1988). Finally, some of the finest examinations of the functional and numerical responses of predators to variation in the density of prey have come from studies of shorebirds, especially large-bodied species that afford easy quantification of intake rate in association with prey density. Notable among shorebirds is the Eurasian Oystercatcher (Goss-Custard 1996), which is an ideal subject for understanding the interrelationships between food availability, foraging behavior, and population size owing to its ease of observation and relatively simple diet of bivalves, mussels, and marine worms.
DIVERSE SOCIAL SYSTEMS
The social systems of shorebirds, their mating relationships, and their patterns of parental care during the breeding season as well as their flocking tendencies during the nonbreeding season are intriguingly diverse. This diversity has been the subject of several reviews (e.g., Oring 1982, 1986; Myers 1984; Goss-Custard 1985). Mating systems run the gamut from extreme polygyny in the lek-breeding Buff-breasted Sandpiper and Ruff to classic polyandry in the phalaropes, jacanas, painted snipes, and various sandpipers. However, the mating systems of most species are characterized by monogamy and varying degrees of shared parental care of eggs and chicks. In the sandpipers, monogamy is the rule, but biparental care of eggs and chicks is highly variable. Females typically depart from breeding areas at variable times after their young have hatched and leave parental care to their mates. Coupled with this diversity of social systems is a pattern of reversed size dimorphism, with females substantially larger than male (Jönsson and Alerstam 1990). This pattern is shared with raptors, which has spawned considerable discourse on the evolution of reversed size dimorphism (Jehl and Murray 1986).
Once they depart from their breeding grounds, most shorebirds typically become much more gregarious. They migrate and winter together in flocks of varying size and density; some species, however, remain solitary throughout the nonbreeding season. The varied flocking tendencies exist both within and among species. As a result, shorebirds have been popular research subjects in weighing the costs and benefits of group living. The attributes that make them ideal subjects include that (1) they are readily observed in open habitats where their foraging behavior is easily quantified, (2) they are common prey of raptors, and (3) they frequently and increasingly interfere with one another's foraging as the flock's size increases. Interestingly, when they are not feeding, shorebirds form dense, mixed-species flocks at roosts. This observation alone suggests that predation has played a strong selective role in shaping this facet of their behavior.
GLOBE-TROTTING MIGRANTS
Most shorebirds—and nearly all sandpipers—breed in northern latitudes where environmental conditions are favorable for breeding. There is a seasonal pulse of food in tremendous abundance, which fuels reproduction by adults and the rapid growth of their young. Northern latitudes also tend to have lower predation pressure on the ground nests of shorebirds. But these environs quickly become inhospitable, and shorebirds must depart to temperate latitudes for the winter.
Most shorebirds undertake short-to long-distance migrations. The exceptions are temperate and tropical species in which some or all individuals in a population migrate short distances. During migration, individuals may spend days, weeks, or months in purposeful, directed movement, with staging at freshwater wetlands and coastal estuaries where they refuel for the next step in their journey. The distance of individual legs of the journey is probably influenced most by the geographical barriers that confront them. For instance, oceanic crossings and passages across inhospitable desert regions (such as the Sahara) are accomplished in a single nonstop flight. When geography and landscape features permit, birds move comparatively short distances among estuaries scattered along continental shorelines. Occasionally, the adaptations for long-distance migrants are nothing short of phenomenal. In the case of the Bar-tailed Godwit, virtually all individuals that breed in western Alaska will stage on the Alaskan peninsula and await favorable weather conditions to carry them nonstop over 11,000 km to wintering areas in New Zealand (Gill et al. 2005). As an adaptation for weight conservation, the godwits' guts atrophy in the weeks just before departure; they regain their mass and function after arrival in their winter quarters (Piersma and Gill 1998).
The nature of shorebird migrations varies within species as well. For instance, the various subspecies of Dunlin migrate along distinct flyways. Such information argues strongly for the conservation of separate populations (subspecies) of Dunlin rather than for a single world population. Even within populations of some species, individuals vary in their migratory nature, yielding classic examples of partial migrants. For example, the population of the Snowy Plover breeding along the Pacific coast of North America consists of both migrants and year-round residents (Stenzel et al. 2008).
WETLAND DEPENDENCE
For much of the year, most shorebirds are intimately tied to open habitats, especially wetlands. In the Arctic, they breed amid tundra wetlands; in temperate regions they are intimately associated with freshwater and hypersaline wetlands. During migration, they concentrate at coastal estuaries and interior wetlands where they rely on food resources to fuel subsequent movements. Worldwide, wetlands are some of the most threatened habitats. The reliance of shorebirds on wetlands has focused conservation (Senner and Howe 1984; Myers et al. 1987) and management (e.g., Eldridge 1992; Helmers 1992) strategies on these valuable habitats. Accordingly, various international treaties (Ramsar Convention of 1971), federal laws (Migratory Bird Treaty Act, North American Wetland Conservation Act), and programs spearheaded by nongovernmental organizations (Western Hemi sphere Shorebird Reserve Network) have been enacted or developed to enhance wetland conservation and management. The recent literature also has produced an abundance of papers addressing the management of wetlands for shorebirds and the integration of their needs with those of other wildlife. Humans have degraded wetland habitats through development of port facilities, pollution, overharvesting of bait and shellfish, and other activities that disrupt the normal activity patterns of shorebirds. Because shorebirds occupy these threatened habitats, management and conservation of wetlands are imperative for the maintenance of viable shorebird populations. In some cases, agricultural lands, pasturelands, and commercial salt production ponds provide important habitats that may be functionally equivalent to seminatural wetlands for large numbers of shorebirds.
CONSERVATION AND MANAGEMENT
The remarkable features that characterize shorebirds are rivaled by the dire conservation status of many species. Several species, such as the Black Stilt of New Zealand and the Spoon-billed Sandpiper of northeastern Russia, are among the rarest birds in the world. Conservationists, ornithologists, and birders worldwide still hold out hope that the Eskimo Curlew persists somewhere in the Canadian Arctic. In the Palearctic, similar hopes prevail for the Slender-billed Curlew, although there have been very few recent sightings. One subspecies of Red Knot was recently proposed for "emergency listing" as endangered under the U.S. Endangered Species Act owing to the most precipitous population decline witnessed in the history of avian conservation (Baker et al. 2004; Niles et al. 2008). Although other populations are quite abundant, their numbers are declining worldwide. In fact, nearly 50% of the world's shorebird populations with known trends are in decline (Zöckler et al. 2003; Thomas et al. 2006). Collectively, these observations have created a growing interest in applied ecology directed at ameliorating the limiting factors that are responsible for the small and declining populations of shorebirds.
RATIONALE FOR AND ORGANIZATION OF THIS BOOK
Over the years, the biology of individual shorebird species has been detailed in countless scientific papers and numerous books (e.g., D. Nethersole-Thompson 1973; D. Nethersole-Thompson and M. Nethersole-Thompson 1979; Goss-Custard 1996; Byrkjedal and Thompson 1998). Additional details on species exist in various regional (Cramp and Simmons 1983; Birds of North America accounts) or global compendia (e.g., Johnsgard 1981; del Hoyo et al. 1992), which are invaluable data sources. In the recent past, several general texts have been published, often with multiauthored chapters covering specialized facets of shorebird biology (e.g., Hale 1980; Burger and Olla 1984a, 1984b; Evans et al. 1984). Several ageing and sexing (Prater et al. 1977; Pyle 2008) or field identification (e.g., Hayman et al. 1986; Paulson 2005; O'Brien et al. 2006) guides exist. One recent compilation (van de Kam et al. 2004) has received considerable praise for melding biology with beautiful images that detail the annual cycle of shorebirds. Surprisingly, however, no text or reference has been compiled for shorebirds. By contrast, both waterfowl and raptors have been the subject of books addressing their ecology, conservation, and management (e.g., Bellrose 1976; Ferguson-Lees and Christie 2005; Balldassarre and Bolin 2006). Hence, there seems a clear need for this book.
I wrote this book based on what I perceived as the lack of a general source of information on the ecology, conservation, and management of shorebirds. I organized the book around a semester-long course that I have taught at Humboldt State University for much of the past 20 years. I begin with a general treatment of the evolutionary relationships of shorebirds, their fossil history, and their contemporary distributions. I then define shorebirds by detailing their anatomy, morphology, and physiology. The discussion of breeding includes chapters on facets of breeding biology that have fascinated biologists for de cades, including mating systems, courtship behavior, egg laying, incubation, and nesting ecology. Next is a discussion of migration, with a treatment of flyways and staging areas, and the evolution of migration strategies. The chapters on winter ecology cover foraging behavior, roosting ecology, social organization, and population ecology. The final chapters cover applied ecology with topics on wetland management, managing predation during the breeding season, and disturbance by humans.
(Continues...)
Excerpted from Shorebird Ecology, Conservation, and Management by Mark A. Colwell. Copyright © 2010 the Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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Table of Contents
Preface and AcknowledgmentsPart I Evolutionary Relationships, Anatomy and Morphology, and Breeding Biology
1 INTRODUCTION
Diversity and Distribution
Varied Ecomorphology
Diverse Social Systems
Globe- Trotting Migrants
Wetland Dependence
Conservation and Management
Rationale for and Organization of this book
2 SYSTEMATICS, PHYLOGENY, AND PHYLOGEOGRAPHY
Fossil History
A Brief History of Shorebird Systematics
Phylogeography
Hybridization in Shorebirds
Biogeography and Communities
Conservation Implications
3 MORPHOLOGY, ANATOMY, AND PHYSIOLOGY
Skeletal and Muscle System
Integumentary System
Sensory Apparatus, Foraging, and Digestion
Digestive System
Energetics and Thermoregulation
Osmoregulation
Reproductive System
Conservation Implications
4 MATING SYSTEMS
Defining a Mating System
The Role of Ecological Factors
Social versus Gene tic
Relationships
Parental Care Patterns
Evolution of Polyandry
Variance in Reproductive Success
Size Dimorphism
Sex Ratios
Conservation Implications
5 BREEDING BIOLOGY
Philopatry, Breeding Site Fidelity, and Dispersal
Spring Arrival Schedules
Courtship Behavior
Breeding Densities
Selection of a Breeding Site
Eggs
Incubation
Hatching
Chick Growth and Development
Conservation Implications
Part II Nonbreeding Ecology and Demography
6 MIGRATION
Origins and Evolution
Migration Strategies
Physiology of Migration
Hop, Skip, and Jump
Populations and Flyways
Conservation Implications
7 FORAGING ECOL OGY AND HABITAT USE
Diets
Foraging Maneuvers and Habitat Use
Acquiring Energy
Food Availability
Individual Variation
Conservation Implications
8 SHOREBIRDS AS PREDATORS
Shorebird Predators and Their Prey
Predicting Wetland Use
Competition and Food Limitation
Prey Reduction
Community Ecology
Conservation Implications
9 SPATIAL ECOLOGY AND WINTER SOCIAL ORGANIZATION
Quantifying Spatial Distributions
A Range of Social Organization
Roosts
Conservation Implications
10 POPULATION BIOLOGY
Demography
Survival
Productivity
Population Sizes and Trends
Monitoring Programs
Limiting Factors
Human Impacts
Conservation Implications
Part III Management and Conservation
11 HABITAT CONSERVATION AND MANAGEMENT
Decision Making in Wildlife Management
Wetland Conservation
Conservation Planning and Implementation
Wetland Management
Agricultural Lands
Salt Ponds
Sandy, Ocean- Fronting Beaches
Conservation Implications
12 MANAGING PREDATORS
Ethical Considerations and Decision Making
Do Predators Limit Shorebird Populations?
Methods of Control
Conservation Implications
13 MANAGING HUMAN DISTURBANCE
Definitions of Human Disturbance
Characterizing Disturbance
Responses to Disturbance
Managing Disturbance
Conservation Implications
14 EDUCATION AND OUTREACH
Professional Groups
Environmental Education
Ecotourism and Birding Festivals
Books and Online Resources
Conservation Implications
Appendix
Index
What People are Saying About This
"This comprehensive text explores the ecology, conservation, and management of these fascinating birds."—The Guardian
"A fine book."—Choice
"[This book] will fill an important need for information on a group of birds whose existence is being threatened. . . . Recommended."—Choice
"A pleasure to read and a real asset to a biologist's bookshelf; both as a reference and as a source of inspiration."—Emu-Austral Ornithology
"It is not often that one picks up a book and realizes he . . . has been missing it for years without realizing it."—The Condor