Most populations of migrant shorebirds around the world are in serious decline, suggesting that vital condition-dependent rates such as fecundity and annual survival are being affected globally. A striking example is the red knot (Calidris canutus rufa) population wintering in Tierra del Fuego, which undertakes marathon 30,000 km hemispheric migrations annually. In spring, migrant birds forage voraciously on horseshoe crab eggs in Delaware Bay in the eastern USA before departing to breed in Arctic polar deserts. From 1997 to 2002 an increasing proportion of knots failed to reach threshold departure masses of 180-200 g, possibly because of later arrival in the Bay and food shortage from concurrent over-harvesting of crabs. Reduced nutrient storage, especially in late-arriving birds, possibly combined with reduced sizes of intestine and liver during refuelling, had severe fitness consequences for adult survival and recruitment of young in 2000-2002. From 1997 to 2002 known survivors in Delaware Bay were heavier at initial capture than birds never seen again, annual survival of adults decreased by 37% between May 2000 and May 2001, and the number of second-year birds in wintering flocks declined by 47%. Population size in Tierra del Fuego declined alarmingly from 51,000 to 27,000 in 2000-2002, seriously threatening the viability of this subspecies. Demographic modelling predicts imminent endangerment and an increased risk of extinction of the subspecies without urgent risk-averse management.

Since 1985, avian influenza virus surveillance has been conducted annually from mid-May to early June in charadriiform species from the families Scolopacidae and Laridae (shorebirds and gulls) at Delaware Bay in the northeast United States. The mass migrations of shorebirds, gulls and horseshoe crabs (Limulus polyphemus) coincide at that time, and large numbers of migrating birds pause at Delaware Bay to feed on horseshoe crab eggs deposited at the high-tide line. Influenza viruses are consistently isolated from charadriiform birds at Delaware Bay, at an overall rate approximately 17 times the combined rate of isolation at all other surveillance sites worldwide (490 isolates/9474 samples, 5.2% versus 49 isolates per 15 848 samples, 0.3%, respectively; Proportion test, p , 0.0001). The likelihood of isolating influenza viruses at Delaware Bay is dependent on the presence of ruddy turnstone (Arenaria interpres) at the sampling site (G-test of independence, p , 0.001). The convergence of host factors and environmental factors results in a unique ecological 'hot spot' for influenza viruses in Charadriiformes.

Wild birds have been implicated in the emergence of human and livestock influenza. The successful prediction of viral spread and disease emergence, as well as formulation of preparedness plans have been hampered by a critical lack of knowledge of viral movements between different host populations. The patterns of viral spread and subsequent risk posed by wild bird viruses therefore remain unpredictable. Here we analyze genomic data, including 287 newly sequenced avian influenza A virus (AIV) samples isolated over a 34-year period of continuous systematic surveillance of North American migratory birds. We use a Bayesian statistical framework to test hypotheses of viral migration, population structure and patterns of genetic reassortment. Our results reveal that despite the high prevalence of Charadriiformes infected in Delaware Bay this host population does not appear to significantly contribute to the North American AIV diversity sampled in Anseriformes. In contrast, influenza viruses sampled from Anseriformes in Alberta are representative of the AIV diversity circulating in North American Anseriformes. While AIV may be restricted to specific migratory flyways over short time frames, our large-scale analysis showed that the long-term persistence of AIV was independent of bird flyways with migration between populations throughout North America. Analysis of long-term surveillance data provides vital insights to develop appropriately informed predictive models critical for pandemic preparedness and livestock protection.

ABSTRACT:Birds in the order Charadriiformes were sampled at multiple sites in the eastern half of the continental USA, as well as at Argentina, Chile, and Bermuda, during 1999-2005, and tested for avian influenza virus (AIV). Of more than 9,400 birds sampled, AIV virus was isolated from 290 birds. Although Ruddy Turnstones (Arenaria interpres) comprised just 25% of birds sampled, they accounted for 87% of isolates. Only eight AIV isolations were made from birds at four locations outside of the Delaware Bay, USA, region; six of these were from gulls (Laridae). At Delaware Bay, AIV isolations were predominated by hemagglutinin (HA) subtype H10, but subtype diversity varied each year. These results suggest that AIV infection among shorebirds (Scolopacidae) may be localized, species specific, and highly variable in relation to AIV subtype diversity.

In studies of forest fragmentatior~ a fundamental inconsistency exists in the distance criterion used to define the discreteness of forest fragmentx We examined three types of ubiquitous, narrow, forest-dividing corridors for effects that influence the relative abundance and community cornposition of forest.nesting birdg Fixed-radius (100-meter) point counts were conducted on 54 transects established along three width classes of corridors: unpaved roads (8 meters wide), paved roads (16 meters wide), and powerlines (23 meters wide). Transect locations were distributed equally among corridor edge forest margin 100 meters from corridor edge and forest interior 300 meters from corridor edge Forest-interior species of Neotropical migrants had significantly reduced relative abundances on edge transects along 16-and 23-meter corridorg compared with 8-meter corridors and with forest interior points along all three corridor-width classe£ At a landscape scal~ the consequences of corredores angostos divisorios del bosque pueden funcionar como trampas ecol6gicas para los migrantes neotropicales del interior del bosque. Sugerimos que estos corredores de amplia distribuci6n pueden ser poco conspicuos, pero contribuyentes importantes en la disminuci6n de las especies del interior de bosque en el este de Norte AmdricaL

Summary 1.Millions of shorebirds migrate each year through a small number of highly productive staging areas where they often conflict with fisheries interests. Delaware Bay, USA, is a major shorebird stopover site where, in spring, many thousands of shorebirds undergo rapid mass gain by feeding on the eggs of commercially harvested horseshoe crabs Limulus polyphemus . 2. Environmental factors may cause deviations from the best migration schedule. We used within-year mass gain data from red knot Calidris canutus caught in Delaware Bay between 1998 and 2005 to determine the degree of flexibility individuals have to vary migration speed. 3. Mass gain by birds below 133 g was shown to comprise 15·3% fat (39 kJ g − 1 ), the remainder being lean mass (6 kJ g − 1 ). Above this critical level, fat comprised 83·9% of mass deposition. The rates of energy deposition (kJ d − 1 ) were therefore fundamentally different between the two states but were among the highest ever recorded among vertebrates (5-7 × basic metabolic rate). 4. A total of 36-62% of the variation in observed rates of energy deposition between 1998 and 2002 was explained by a year factor, date and mass at initial capture and interaction terms, such that light-weight birds at the end of May had rates of mass gain or energy deposition two to three times higher than birds of similar mass in mid-May, indicating that birds were attempting to achieve a certain mass by a certain date. In 2003 and 2005, this relationship broke down as a result of lower densities of eggs. 5. Synthesis and application. The maintenance of high densities of crab eggs required for high rates of mass gain in red knot requires severe cuts in, or the complete cessation of, the crab harvest, reduced human and raptor-related disturbance as well as management of beaches to provide sufficient crab-spawning habitat. These findings are widely applicable to other systems where harvesting activities come into conflict with migrating animals and show that certain sections of the population, in this case the long-distance migrants from South America, will be impacted more than short-distance migrants whose physiology may give them access to alternative food resources.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. University of California Press and CooperOrnithological Society are collaborating with JSTOR to digitize, preserve and extend access to The Condor. Abstract. Northbound migrant shorebirds (Charadridae and Scolopacidae) were surveyed weekly by air on Delaware Bay beaches on the Atlantic coast of North America inMay-June 1986 through 1992. The single day peak count occurred between 26-30 May when an average of more than 216,000 birds was counted. The most abundant species were Semipalmated Sandpiper (Calidris pusilla), Ruddy Turnstone (Arenaria interpres), Red Knot (Calidris canutus) and Sanderling (Calidris alba). Our surveys documented high hemispheric counts for each of these species, and established Delaware Bay as the most important spring stopover in the eastern U.S. for these shorebirds. Counts of Sanderlings and Semipalmated Sandpipers declined significantly over the seven years; no trends for other species were detected. Differences among species in distribution along bay beaches were attributable partly to habitat factors. We suggest that a thorough understanding of shorebird abundance and habitat use in Delaware Bay is necessary to develop a conservation strategy for regulatory protection and conservation of migrant shorebirds using this area.

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