Brian A. Harrington

The impact of human disturbance on shorebirds at a migration staging area

Abstract Human disturbance was investigated as a factor that might limit the capacity of a staging area to support migrating shorebirds. Long-term census data were used to test the hypothesis that human disturbance at an important coastal migration staging area has a negative impact on shorebird movement patterns because of (1) displacement of shorebirds from preferred resting areas within the study area; and (2) abandonment of the study area. Results revealed that four of seven species showed one or more types of movement in response to disturbance. The impact of disturbance was greater on species using the heavily distributed front side of the beach. The abundance of impacted species may be reduced by 50% at high disturbance levels. Abundance of front-beach species, such as red knot Calidris canutus and short-billed dowitcher Limnodromus griseus, declined between 1972 and 1989 more than back-beach species, such as black-bellied plover Pluvialis squatarola and semipalmated plover Charadrius semipalmatus; red knot and short-billed dowitcher declined more at Plymouth Beach than at two comparable, but less disturbed, coastal staging areas and more than the overall eastern North American population. Disturbance is implicated as a potential factor in long-term declines in shorebird abundance at Plymouth Beach. The impacts of disturbance could be reduced or perhaps eliminated by closing one or more small portions of the front beach as refuge resting areas during migration.

Population trends of North American shorebirds based on the International Shorebird Survey

Abstract Shorebirds Charadrii are prime candidates for population decline because of their dependence on wetlands that are being lost at a rapid pace. Thirty-six of the 49 species of shorebirds that breed in North America spend most of the year in Latin America. Because populations of most species breed and winter at remote sites, it may be most feasible to monitor their numbers at migration stopovers. In this study, we used statistical trend analysis methods, developed for the North America Breeding Bird Survey, to analyze data on shorebird populations during southbound migration in the United States. Survey data were collected by volunteers in the International Shorebird Survey (ISS). The analyses indicate that whimbrels Numenius phaeopus, short-billed dowitchers Limnodromus griseus, and sanderlings Calidris alba have undergone statistically significant declines. Methodological concerns over both the ISS and the trend analysis procedures are discussed in detail and biological interpretations of the results are suggested.

WESTERN SANDPIPERS (CALIDRIS MAURI) DURING THE NONBREEDING SEASON: SPATIAL SEGREGATION ON A HEMISPHERIC SCALE

Abstract The nonbreeding distribution of Western Sandpipers (Calidris mauri) was documented using 19 data sets from 13 sites along the Pacific and Atlantic coasts of the Americas. Western Sandpipers showed latitudinal segregation with regard to sex and age. Females wintered farther south than males. A “U” shaped pattern was found with respect to age, with juveniles occurring at higher proportions at both the northern and southern ends of the range. Distribution of sexes might be affected by differences in bill length and a latitudinal trend in depth distribution of prey. For age class distribution, two different life-history tactics of juveniles might exist that are related to the higher cost of feather wear for juveniles compared to adults. Most juveniles complete three long-distance migrations on one set of flight feathers whereas adults complete two. Juveniles may winter either far north, thereby reducing feather wear induced by ultraviolet light, migration, or both, or far south and spend the summer on the nonbreeding area.

Population size and winter distribution of eastern American oystercatchers

Abstract Conservation of the eastern subspecies of the American oystercatcher (Haematopus palliatus palliatus) is a high priority in the U.S. Shorebird Conservation Plan, but previous population estimates were unreliable, information on distribution and habitat associations during winter was incomplete, and methods for long-term monitoring had not been developed prior to this survey. We completed the aerial survey proposed in the U.S. Shorebird Conservation Plan to determine population size, winter distribution, and habitat associations. We conducted coastal aerial surveys from New Jersey to Texas during November 2002 to February 2003. This area comprised the entire wintering range of the eastern American oystercatcher within the United States. Surveys covered all suitable habitat in the United States for the subspecies, partitioned into 3 survey strata: known roost sites, high-use habitat, and inter-coastal tidal habitat. We determined known roost sites from extensive consultation with biologists and local experts in each state. High-use habitat included sand islands, sand spits at inlets, shell rakes, and oyster reefs. Partner organizations conducted ground counts in most states. We used high resolution still photography to determine detection rates for estimates of the number of birds in particular flocks, and we used ground counts to determine detection rates of flocks. Using a combination of ground and aerial counts, we estimated the population of eastern American oystercatchers to be 10,971 +/− 298. Aerial surveys can serve an important management function for shorebirds and possibly other coastal waterbirds by providing population status and trend information across a wide geographic scale.

Collaborative approaches to the evolution of migration and the development of science-based conservation in shorebirds

SHOREBIRDS ARE AMONG the most highly migratory creatures on earth. Both the study of their ecology and ongoing efforts to conserve their populations must reflect this central aspect of their biology. Many species of shorebirds use migration and staging sites scattered throughout the hemisphere to complete their annual migrations between breeding areas and nonbreeding habitats (Morrison 1984). The vast distances between habitats they use pose significant challenges for studying their migration ecology. At the same time, the large number of political boundaries shorebirds cross during their epic migrations create parallel challenges for organizations working on their manage

MOLT AND BODY MASS OF RED KNOTS IN THEEASTERN UNITED STATES

Abstract Red Knots (Calidris canutus) that spend winter in the southeastern United States are known to have been genetically separated from their congeners that migrate to Patagonian wintering grounds for about 12,000 years. We examined and documented differences between the two groups in their use of southward migration stopover locations, flight feather molt, fidelity to wintering zones, and differences in mass at southward migration stopover locations. Red Knots wintering in the southeastern United States do so consistently, and knots wintering in Patagonia have not changed to wintering in the southeastern United States. The two wintering groups have distinct differences in their nonbreeding season biology (e.g., migration strategies, chronology of pre-basic molt), and these differences have been maintained for decades if not millennia.