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Article Excerpt
ABSTRACT. Available information on the distribution of breeding shorebirds across the Arctic Coastal Plain of Alaska is dated, fragmented, and limited in scope. Herein, we describe the distribution of 19 shorebird species from data gathered at 407 study plots between 1998 and 2004. This information was collected using a single-visit rapid area search technique during territory establishment and early incubation periods, a time when social displays and vocalizations make the birds highly detectable. We describe the presence or absence of each species, as well as overall numbers of species, providing a regional perspective on shorebird distribution. We compare and contrast our shorebird distribution maps to those of prior studies and describe prominent patterns of shorebird distribution. Our examination of how shorebird distribution and numbers of species varied both latitudinally and longitudinally across the Arctic Coastal Plain of Alaska indicated that most shorebird species occur more frequently in the Beaufort Coastal Plain ecoregion (i.e., closer to the coast) than in the Brooks Foothills ecoregion (i.e., farther inland). Furthermore, the occurrence of several species indicated substantial longitudinal directionality. Species richness at surveyed sites was highest in the western portion of the Beaufort Coastal Plain ecoregion. The broad-scale distribution information we present here is valuable for evaluating potential effects of human development and climate change on Arctic-breeding shorebird populations.
Key words: Alaska, Arctic, birds, breeding shorebirds, coastal plain, distribution, North Slope
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RESUME. Les renseignements qui existent en matiere de repartition des oiseaux de rivage en reproduction sur la plaine cotiere de l'Arctique en Alaska sont anciens, fragmentes et restreints. Ici, nous decrivons la repartition de 19 especes d'oiseaux de rivage a partir de donnees recueillies a 407 lieux de recherche entre 1998 et 2004. Cette information a ete recueillie grace a une technique de recherche consistant en une seule visite rapide durant les periodes d'etablissement du territoire et de debut d'incubation, periodes pendant lesquelles les comportements sociaux et les vocalisations permettent de bien reperer les oiseaux. Nous decrivons la presence ou l'absence de chaque espece, de meme que le nombre general d'especes, ce qui procure une perspective regionale de la repartition des oiseaux de rivage. Nous comparons et contrastons nos cartes de repartition des oiseaux de rivage a celles d'etudes anterieures, en plus de decrire les tendances les plus marquees en matiere de repartition des oiseaux de rivage. Notre examen de la variation latitudinale et longitudinale en matiere de repartition et de nombre d'especes d'oiseaux de rivage a l'echelle de la plaine cotiere arctique de l'Alaska nous a permis de constater que la plupart des especes d'oiseaux de rivage se manifestaient plus souvent dans la region ecologique de la plaine cotiere de Beaufort (c'est-a-dire plus proche de la cote) que dans la region ecologique des contreforts de Brooks (c'est-a-dire plus a l'interieur des terres). Par ailleurs, l'occurrence de plusieurs especes indiquait une directionalite longitudinale substantielle. La richesse des especes aux sites a l'etude etait a son meilleur dans la partie ouest de la region ecologique de la plaine cotiere de Beaufort. Les renseignements sur la repartition a grande echelle que nous presentons ici jouent un role dans l'evaluation des effets eventuels des travaux de mise en valeur par l'etre humain et du changement climatique sur les populations d'oiseaux de rivage en reproduction de l'Arctique.
Mots cles: Alaska, Arctique, oiseaux, oiseaux de rivage en reproduction, plaine cotiere, repartition, versant nord
Traduit pour la revue Arctic par Nicole Giguere.
INTRODUCTION
During June-September, the Arctic Coastal Plain of Alaska (hereafter Coastal Plain) provides important habitat for millions of shorebirds that breed in and migrate through the area (Johnson and Herter, 1989). At least 29 species breed on the Coastal Plain, and as many as six million birds are estimated to occur in the National Petroleum Reserve-Alaska (NPR-A) alone (King, 1979). These shorebirds and many other bird species migrate to nonbreeding areas in the southern parts of the Western Hemisphere, Southeast Asia, Oceania, Australia, and New Zealand (Hayman et al., 1986).
The worldwide populations of many shorebird species, including species that breed on the Coastal Plain, have recently declined (Brown et al., 2001; International Wader Study Group, 2003). Declines are suspected or have been documented for 11 shorebird species that regularly breed on the Coastal Plain (U.S. Shorebird Conservation Plan, 2004), and nine of these species have been classified as species of high concern or as highly imperiled at a hemispheric or global level (U.S. Shorebird Conservation Plan, 2004). Furthermore, the majority of the U.S. breeding populations of seven species occurs on the Coastal Plain (Alaska Shorebird Working Group, 2000).
Human alteration of land on the Coastal Plain may have negative consequences for shorebirds. New and expanding native villages, along with a recently legalized spring and summer subsistence harvest of shorebirds (Alaska Migratory Bird Co-Management Council, 2003), may negatively affect shorebirds through habitat alteration, hunting mortality, and subsequent population reduction. Oil production in the central portion of the Coastal Plain began in 1977 (Gilders and Cronin, 2000), and oil development has expanded in all directions over the past 30 years (National Research Council, 2003). Besides the initial Prudhoe Bay Oil Field, at least nine additional fields have begun production (Gilders and Cronin, 2000). Recently, areas within the NPR-A previously closed to oil and gas exploration and development have been leased (U.S. Bureau of Land Management, 2006). Legislation has also been proposed to authorize oil exploration and development in a designated section (1002 Area) of the coastal plain of the Arctic National Wildlife Refuge (Arctic Refuge). Potential effects of oil and gas development on wildlife include the loss of habitat through the building of roads, pads, pipelines, dumps, gravel pits, and other infrastructure. Roads and pads also increase levels of dust, alter hydrology, thaw permafrost, and increase roadside snow accumulation (Auerbach et al., 1997; National Research Council, 2003). These impacts may decrease habitat quantity and quality for nesting shorebirds (Meehan, 1986; Troy Ecological Research Associates, 1993a; Auerbach et al., 1997). Furthermore, oil field infrastructure may enhance predator numbers by providing denning and nesting habitat and supplemental food (through human garbage) during winter months. An increase in predators may result in lower adult shorebird and nest survival (Eberhardt et al., 1983; Day, 1998; National Research Council, 2003). Lower adult survival and nesting success may create population sinks in the vicinity of human developments (National Research Council, 2003), especially for species with high site fidelity. Therefore, expanding oil development could have cumulative negative effects on breeding shorebirds of the Coastal Plain.
Climate change may also affect shorebird habitats and populations on the Coastal Plain by altering coastal and inland tundra habitats (Arctic Climate Impact Assessment, 2004). A rise in sea level is expected to change rates of sedimentation, permafrost aggradation and degradation, storm frequency, and subsidence; all of these factors are likely to influence coastal geomorphology and perhaps invertebrate communities (Jorgenson and Ely, 2001; Rehfisch and Crick, 2003). These changes may negatively affect shorebirds breeding in low-lying areas or staging in littoral areas prior to fall migration. Other habitat-altering effects are also likely. For example, climate models predict longer growing seasons and warmer temperatures, which are already thought to be responsible for northward advancement of shrubs (Sturm et al., 2001; Arctic Climate Impact Assessment, 2004). In addition, accelerated ice wedge degradation and accompanying thermokarst pond development have increased the proportion of land covered with surface water (Shur et al., 2003). These habitat changes may have both positive and negative effects on a particular shorebird species, and assemblage-wide effects are difficult to predict. Beyond direct effects on habitat conditions, earlier snowmelt may decouple the apparent synchrony between shorebird breeding chronology and food availability (MacLean, 1980). The timing and availability of surface-active insects is critical to shorebirds for egg production (Klaassen et al., 2001), chick growth (Schekkerman et al., 2003), and pre-migratory fattening (Connors etal., 1979, 1981; Connors, 1984; Andres, 1994). Decoupling of these events could negatively affect shorebird productivity and survival.
An important step in evaluating the potential impacts of human activities and climate change on shorebirds in the Coastal Plain is to document the current distribution of species. The earliest avifaunal accounts of coastal northern Alaska came from naturalists participating in Arctic expeditions (Nelson, 1883; Stone, 1900; Bishop, 1944), followed by museum collectors (Bailey, 1948) and taxonomists (Bee, 1958; Gabrielson and Lincoln, 1959; Kessel and Gibson, 1978; Gibson and Kessel, 1997). These accounts included natural history observations and a limited number of locations where species were collected or observed breeding. Quantitative ornithological studies on the Coastal Plain began with the International Biological Programme and the Coastal Tundra Biome Studies at Barrow in the 1970s (Brown et al., 1980). These programs focused on studies of breeding and postbreeding shorebirds (Pitelka, 1974; Myers and Pitelka, 1980). In anticipation of oil development, the U.S. government also initiated the Outer Continental Shelf Environmental Assessment Program (OCSEAP), which documented the nearshore marine resources along the Beaufort Sea coast (Engelmann, 1976; Connors et al., 1979; Barnes et al., 1984). Extensive aerial and ground-based surveys were also conducted in and outside of the Prudhoe Bay region (Gavin, 1975; Haddock and Evans, 1975; Norton et al., 1975; Bergman et al., 1977; Derksen et al., 1981). The potential for future oil development led to two additional large-scale ground studies on tundra areas in north-central Alaska (Field, 1993) and the Arctic Refuge (Garner and Reynolds, 1986). Additional pre-development and, more rarely, post-development studies of avifauna at oil exploration sites have been conducted (e.g., Martin and Moitoret, 1981; Andres, 1989; Troy and Carpenter, 1990; Moitoret et al., 1996; Anderson et al., 2000; Cotter and Andres, 2000; Johnson et al., 2003). Notable contributions include a long-term study of birds at Point McIntyre (Troy Ecological Research Associates, 1993b) and extensive reviews of regional avifauna and their relationship to oilfield infrastructure and activities (Johnson and Herter, 1989; Truett and Johnson, 2000).
Despite more than 100 years of study, specific information on the breeding distribution of birds on the Coastal Plain remains limited and fragmented. This is particularly true for species like shorebirds that cannot be easily counted from aircraft. Unlike most waterfowl species, whose distributions are fairly well known (e.g., Mallek et al., 2004; Larned et al., 2005), shorebirds are described by references based primarily on checklists of birds detected near major villages, at oil field sites, along inland rivers, and at a limited number of remote inland sites (e.g., Bailey, 1948; Gabrielson and Lincoln, 1959; Kessel and Gibson, 1978; Johnson and Herter, 1989). Species distribution maps from the Birds of North America series (Poole and Gill, 2005) and field guides (e.g., Sibley, 2000; National Geographic Society, 2002) are very general, and may not accurately depict the regional distribution of shorebirds on the Coastal Plain.
As a first step towards a better description of shorebird distribution throughout the Coastal Plain, we conducted ground surveys at 625 sites. We report here the distribution of 19 species of breeding shorebirds and compare these results with previous descriptions of species distributions. We also evaluate patterns of species occurrences and species richness along latitudinal and longitudinal gradients defined by natural physiographic features.
STUDY AREA
Our study area in northern Alaska included land lower than 350 m in elevation north of the Brooks Range between Icy Cape in western Alaska and the Aichilik River near the Canadian border (Fig. 1). We chose 350 m as the elevation limit because the majority of shorebirds breed below this elevation (Johnson and Herter, 1989). The 107000 [km.sup.2] study area is approximately 850 km from east to west and 25-220 km from north to south. Sampling was conducted in the Colville River delta and the eastern portion of the NPR-A in 1998-2000, throughout the NPR-A (from Icy Cape to the Colville River)...
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