WILDLIFE SCIENCE: LINKING ECOLOGICAL THEORY AND MANAGEMENT APPLICATIONS - CHAPTER 5 docx

Basis for An Ecologicalof Wetland Management Birds Guy A Baldassarre CONTENTS Need and Basis for Wetland Management Landscape Ecology and Wetland Management Wetland Plant Succession The Role of Models Taxonomy and Phylogenetic Systematics An Upshot Acknowledgments References 80 82 84 86 88 90 90 91 Wetland birds are species dependent on fresh, salt, or brackish-water wetlands to satisfy most, if not all, life history requirements They are a subset of the larger waterbirds group, which comprises about 800 species dependent on any aquatic habitat, but not necessarily wetlands (Reid 1993) Hence, the wetland birds group excludes all seabirds (e.g., albatrosses, auks, and boobies) and most coastal waterbirds (e.g., gulls, terns, pelicans, and cormorants), but the group is nonetheless still large, diverse, and widely distributed Globally, the wetland birds group comprises about 620 species, of which 197 (31.8%) occur in North America (Table 5.1) The largest groups are the waterfowl (Anatidae — 157 species), followed by the rails, gallinules, and coots (Rallidae — 134 species) Other significant groups are the sandpipers (Scolopacidae — 87 species), plovers (Charadriidae — 66 species), egrets, herons, and bitterns (Ardeidae — 63 species), ibises and spoonbills (Threskiornithidae — 33 species), grebes (Podicipedidae — 19 species), storks (Ciconiidae — 19 species), and cranes (Gruidae — 15 species) Several smaller families of wetland birds contain 1–10 species Unfortunately for wetland birds, wetland habitats of all types have undergone massive loss and alteration In the United States, for example, the “best estimate” is that 89.5 million of wetlands existed in the lower 48 states at the time of colonial America, with another 69 million in Alaska and 24,000 in Hawaii By the mid-1980s, however, only about 42 million remained in the lower 48 states, which represented a loss of 53% (Dahl 1990) Some 22 states have lost 50% or more of their original wetlands; 11 have lost more than 70% By 1997, 42.7 million remained in the lower 48 states, of which 95% were inland freshwater wetlands (Dahl 2000) Globally, wetland loss may approach 50% (Dugan 1993), although loss is more severe in some regions than others Based on a summary appearing in Mitsch and Gosselink (2000, 38), losses exceed 90% in Europe and New Zealand, 60% in China, and more than 50% in Australia Within nations, certain regions or types of wetlands may be particularly affected For example, about 67% 79 © 2008 by Taylor & Francis Group, LLC Wildlife Science: Linking Ecological Theory and Management Applications 80 TABLE 5.1 Global and North American Diversity of Wetland Birdsa Family Anatidae Rallidae Scolopacidae Charadriidae Ardeidae Threskiornithidae Podocipedidae Ciconiidae Gruidae Recurvirostridae Burhinidae Jacanidae Total species Common name Ducks, geese, and swans Rails, gallinules, and coots Sandpipers and allies Plovers and allies Herons, egrets, and bitterns Ibises and spoonbills Grebes Storks Cranes Avocets and stilts Thick-knees Jacanas North American speciesb Global speciesa 157 134 87 66 63 33 19 19 15 10 620 62 17 64 16 16 3 1 197 Percentage of North American species −39.5 12.7 73.6 24.2 −25.4 15.2 −36.8 10.5 20.0 30.0 11.1 12.5 31.8 a Data are from Clements, J F 2000 Birds of the World: A Checklist, 5th edn Temecula, CA: Ibis Publishing b Data are from American Ornithologists’ Union (AOU) 1998 Check list of North American Birds, 7th edn Washington, DC: American Ornithologists’ Union of all mangrove swamps in the Philippines are gone, as are an estimated 80% of the Pacific coastal estuarine wetlands and 71% of the prairie potholes in Canada (Whigham et al 1993) This extensive loss of habitat is exacerbated, because wetland destruction has differentially involved the “best” wetlands for wildlife Such wetlands often occur on the most productive soils for agriculture (e.g., prairie and riparian wetlands), wherein those wetlands strongly compete with humans for space Productive coastal wetlands have been differentially targeted for expansion of coastal cities, shipping channels, and agricultural development, especially rice and various forms of aquaculture (e.g., shrimp) Hence, many of the remaining wetlands in the United States and elsewhere often are poor-quality wildlife habitat For example, in an early assessment of wetlands in the United States and their importance as waterfowl habitat, 70% were ranked as low or of negligible value (Shaw and Fredine 1956) Arctic wetlands are the major exception to this general pattern, because soils are poor and growing seasons short; hence, agricultural activities are virtually nonexistent in the Arctic, and arctic wetlands are critical breeding habitat for some waterfowl and shorebirds Nonetheless, the extensive quantitative and qualitative loss of wetlands has severely affected wetland birds of all taxonomic groups Indeed, in comparison to species numbers summarized in Table 5.1, some 175 (28.2%) are listed by International Union for the Conservation of Nature and Natural Resources (IUCN) in the Red List of Threatened Species (IUCN 2006; Table 5.2); 30 (4.8%) are listed extinct, 21 (3.4%) as critically endangered, 37 (6.0%) as endangered, 46 (7.4%) as vulnerable, and 41 (6.6%) as near threatened (Table 5.2) The most affected group is the cranes (66.6% listed), followed by the rails (35.1%), sandpipers (26.4%), waterfowl (26.1%), herons (20.6%), and plovers (19.7%) NEED AND BASIS FOR WETLAND MANAGEMENT Acquisition, easement, or legal designations cannot adequately protect wetlands, because they are especially subject to rapid changes in structure and plant composition Hence, active management © 2008 by Taylor & Francis Group, LLC Ecological Basis for Management of Wetland Birds 81 TABLE 5.2 Total Number of Species of Wetland Birds Listed in Four Major Categories by the International Union for the Conservation of Nature and Natural Resources (2006) Family Anatidae Rallidae Scolopacidae Charadriidae Ardeidae Threskiornithidae Podocipedidae Ciconiidae Gruidae Recurvirostridae Burhinidae Jacanidae Total Common name Extincta Critically endangered Endangered Vulnerable Near threatened Ducks, geese, and swans Rails, gallinules, and coots Sandpipers and allies Plovers and allies Herons, egrets, and bitterns Ibises and spoonbills Grebes Storks Cranes Avocets and allies Thick-knees Jacanas All species 15 0 0 30 2 1 0 21 3 0 37 12 14 4 1 0 46 8 11 2 41 a Species extinct since 1500 is usually critical to maintain the functional values that led to protection in the first place! Active management of remaining wetlands is especially essential, because a lesser amount of habitat must now maintain population levels of wetland birds and other wetland wildlife once supported by a wetland base nearly twice as large as that in North America today Wetlands management basically synchronizes availability of habitat and habitat components (e.g., food) to coincide temporally and spatially with life history events affecting survival and reproduction of populations of target species or species groups Most wetland birds are migratory, and species-specific migratory patterns, habitat use, and other life history requirements are fairly well known, especially in North America Hence, the spatial and temporal considerations of wetland management (i.e., “where and when”) are well known, and techniques (i.e., “how”) for actual management are very well documented (Payne 1992) However, managers must understand why protection and manipulation of certain habitats benefits some species and species groups but not others, and then reconcile issues of size, juxtaposition, connectivity, and habitat diversity Managers must understand why certain factors are important to issues of biodiversity, because they are now called upon to address an array of wetland-dependent biota in addition to a focus species or group Finally, managers must understand why a particular management technique is warranted in one situation but not another Wetland managers may wish away this level of understanding in the decision-making process, but such complexity is only accelerating with the new millennium, coincident with perhaps the most urgent need ever to protect and manage wetland habitats and associated biota such as wetland birds Further, despite increasing attention to wetland conservation issues everywhere, wetland loss will continue wherein management of remaining wetlands will be of paramount concern Thus, increasingly complex issues will characterize the landscape for wetland managers in the future, but that difficulty is not insurmountable, and certainly not an a priori recipe for failure Wetland managers must understand the ecological underpinnings of certain management approaches (i.e., an ecological approach) to understand why they are successful A “how-to” approach dooms managers to a “hit-or-miss” strategy that is often ineffective, unrepeatable, nontransferable among managers, and costly in terms of both time and money The purpose of this chapter is to demonstrate the value of an ecological approach to the management of wetland birds To achieve © 2008 by Taylor & Francis Group, LLC 82 Wildlife Science: Linking Ecological Theory and Management Applications that objective, I review the ecological basis for four major approaches to wetland management that I believe are most effective in the decision-making process associated with wetland bird conservation and management Two approaches focus on habitat considerations (landscape ecology and wetland plant succession), whereas the other two focus on wetland birds themselves (demographic models and phylogenetics) LANDSCAPE ECOLOGY AND WETLAND MANAGEMENT All wetlands occur as individual entities, but wetlands also aggregate into groups or complexes that spatially occur at scales ranging from local to global, the array of which leads management into the realm of landscape ecology Along the path, managers also confront issues such as wetland size and juxtaposition, as well as assessment of species richness and habitat functions Habitat acquisition and legal protection of wetlands are especially concerned with all of the above issues, and landscape ecology has figured prominently in these deliberations even before its formal emergence in ecology The decision-making tools available to managers have transformed from crude, blackand-white aerial photographs to high-resolution digital satellite images accurate to within a few meters, and the emergence of geographic information systems (GIS) and associated techniques has facilitated detailed quantitative analysis where earlier efforts involved much guesswork Nonetheless, improvement of data quality has not negated application of the principles of landscape ecology to wetland protection efforts Historically, waterfowl managers were perhaps first to use concepts of landscape ecology in association with acquisition of national wildlife refuges Early managers recognized that nearly all species of waterfowl in North American were highly migratory; hence, management efforts were needed to establish refuges on breeding, wintering, and migration areas, if the annual cycle needs of waterfowl were to be satisfied for the array of species involved For migratory birds in general, these issues were later recognized as “connectivity,” which realizes that individuals move back and forth between specific breeding and nonbreeding areas (Webster et al 2002) Regardless, early wetland acquisition efforts often focused on large tracts of wetlands that formed the basis of many national wildlife refuges Small wetland areas received direct focus from the U.S Fish and Wildlife Service with creation of the Waterfowl Production Areas program in 1959, which recognized the importance of small wetlands to breeding waterfowl More detailed relationships about habitat size and species richness of wetland birds stemmed from early studies that spawned the initial theory of “island biogeography,” which established a relationship between the size and isolation of islands and subsequent species richness of birds, spawning the species-area equation now so familiar in conservation biology (MacArthur and Wilson 1967) Subsequent studies examined these issues in an array of insular habitats such as prairies, forests, cemeteries, and, of course, wetlands The first major study occurred in 1983–84 when Brown and Dinsmore (1986) addressed the influence of size and isolation on the diversity of breeding birds in 30 Iowa wetlands ranging in size from 0.2 to 182.0 Data from their study yielded a significant correlation between species richness and wetland area (r = 82) Gibbs et al (1991) later examined use of 87 wetlands in Maine by 15 breeding waterbirds and also found a significant correlation between area and species richness (r = 66) Similarly, Grover and Baldassarre (1995) found wetland area correlated (r = 65 − 66) with richness of wetland birds using active and inactive beaver (Castor canadensis) ponds in south-central New York Relative to isolation of habitats, Brown and Dinsmore (1986) found that total area of wetlands within km of a given wetland explained the most variation in species richness (r = 42), and was the only significant factor among 12 isolation variables measured Indeed, wetlands in complexes had more species (11) but were half as large (14 ha) as isolated wetlands (30 ha, nine species) © 2008 by Taylor & Francis Group, LLC Ecological Basis for Management of Wetland Birds 83 Gibbs et al (1991) found that isolation was weakly correlated (r = 24) with the species richness of birds In a two-variable model, however, wetland size and isolation explained 74% of the variation associated with species richness in Iowa and 43% in Maine These and other studies certainly provide managers with the guidance that protection of large wetlands and wetland complexes will protect species richness Weller (1981) was perhaps the first to promote the idea that protection of a wetland complex was the best way to protect regional wetland flora and fauna Within such complexes, however, protection of small wetlands may be especially significant in designing programs to protect species diversity For example, Gibbs (1993) modeled the effect of removing small wetlands (i.e., 4.05 ha) within a 600-km2 area in Maine that contained 354 wetlands ranging in size from 0.05 to 105.3 Loss of small wetlands reduced total wetland area by only 19% but decreased the total wetland number by 62%, and increased the inter-wetland distance by 67% The simulation predicted that local populations of turtles, small birds, and small mammals faced significant risk of extinction with loss of small wetlands This study thereby underscored the value of small wetlands as a means of maintaining species richness of wetland wildlife, including waterbirds Unfortunately, small wetlands are the easiest wetlands to drain or fill Further, because of their ephemeral nature, small wetlands are often not afforded legal protection and not garner significant attention from managers Hence, despite their importance, small wetlands are often the first to disappear from wetland complexes Large wetlands are, of course, critically important within wetland complexes for many reasons, but particularly because their absence affects area-dependent species For example, in their Iowa study, Brown and Dinsmore (1986) found that 10 of the 25 species detected did not occur in wetlands