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Each May, red knots (Calidris canutus rufa) congregate in Delaware Bay during their northward migration to feed on horseshoe crab eggs (Limulus polyphemus) and refuel for breeding in the Arctic. [...]

Many migratory birds use staging sites to gain essential resources to fuel their ongoing migration. Understanding staging strategies reveals much about migration systems and is essential if one is concerned with monitoring population trends and mass gains, two of the principal methods for assessing the 'health' of a migratory population. In spring 2004, we investigated the staging behavior in Delaware Bay of Red Knot (Calidris canutus) using mark--recapture techniques and resightings of birds marked in the preceding spring. Individuals staged for 11-12 days, which declined to 8-10 days late in the season. Arrivals were asynchronous, but departures tended to be synchronized. A simple sensitivity analysis showed that the mark-recapture analysis estimated length of stay to within +10% and confirmed biases in monitoring trends and mass gains using peak counts and mass-on-date regressions. Alternative methods using staging duration to estimate passage population size and mass gains were shown to be unbiased. Using these methods, we estimated a passage population size in 2004 of 18,000 Red Knot that arrived at an average mass of 111 g and, on average, gained mass at 7.2 g [day.sup.-1]. Thus, in 2004, the passage population was substantially smaller than the recent peak count of 50,360 in 1998, which confirms a significant decline in the number of Red Knot staging in Delaware Bay. Use of refined techniques such as these is essential if management decisions such as those in Delaware Bay are to be based on firm scientific advice. Key words: Calidris canutus, Delaware Bay, mark-recapture models, mass gain, passage population size, Red Knot, staging ecology, turnover.

Surveys of the North American race of the Red Knot (Calidris canutus rufa) on its main wintering areas on the coasts of Patagonia and Tierra del Fuego (Argentina and Chile) showed a dramatic decline in the wintering population: totals in 2003 were about 30 000 compared to 67 500 in the mid-1980s. Numbers at the principal wintering site, Bahia Lomas, fell by approximately 50%, from 45 300 in 2000 to 22 000-25 000 in 2002-2003. Numbers at peripheral sites on the coast of Patagonia declined dramatically, decreasing 98% compared to numbers in the mid-1980s. The results showed that declines at core sites did not result from birds moving to other places within the known wintering (or other) areas, but reflected a general population decline, with most birds now restricted to key sites in Tierra del Fuego. This phenomenon may explain why long-term declines noted elsewhere have only recently become apparent at key wintering areas. Possible reasons for the declines are discussed. Banding studies in Delaware Bay have shown that in recent years an increasing proportion of Red Knots is unable to gain sufficient weight for migration to the breeding grounds. This is likely due to reductions in their main food resource, eggs of the horseshoe crab Limulus polyphemus. The resulting increase in mortality could account for the magnitude and severity of the declines we observed. Key words: conservation, declines, population, Red Knot, shorebirds.

Physical factors such as wind direction and speed have little effect on the number of raptors on Cape May peninsula, New Jersey. The need to hunt and the need for suitable habitats influences the density of raptors. Densities are higher and extend to lower altitudes over habitats similar to those encountered during breeding and wintering seasons. Migratory raptors forage on migratory birds, fish, and insects that gather at the end of Cape May peninsula or in the offshore waters. A high proportion of the raptors are immature and inexperienced and the presence of similarly immature prey affects migration along the coast.

Observations of the spring migration activity and stoppages on Delaware Bay beaches of shorebirds revealed that this is the most prominent stopover zone in the Western Hemisphere. Increased human activity, environmental contamination and risk due to toxic accidents endanger the habitats and food resources of the shorebirds during migration to Delaware Bay. Foraging zones shift significantly, subsequent to human disturbances. Oil spills and habitat modification could result in unfavorable alterations to the birds' feeding and roosting habits.

To determine if contaminants contributed to low hatching success of ospreys (Panditon haliaetus) nesting near Delaware Bay, we compared levels of organochlorines, mercury, and lead in addled and randomly collected eggs and potential prey from Delaware Bay to a successful population along the Atlantic Coast (

Reestablishment of the peregrine falcon (Falco peregrinus) as a breeding bird in the eastern United States is a highlight in endangered species management and recovery programs. We examined numbers of pairs, reproductive success, and eggshell thinning of a reestablished peregrine falcon population in New Jersey during 1979-88. Productivity of these falcons (x = 1.38 young fledged/pair) was comparable with that of stable populations, but productivity was lower (P = 0.02) for pairs near Delaware Bay and River (0.58 young/pair) compared to those in other regions of New Jersey (1.55 young/pair). Lower productivity and nest success of 4 pairs near Delaware Bay and River that we studied intensively in both 1987 and 1988 were due to low hatching success and predation, probably by great horned owls (Bubo virginianus). During 1985-88 eggshell thickness from New Jersey peregrines averaged 16.4% below pre-DDT levels and apparently has decreased steadily since 1979. This decrease in eggshell thickness statewide suggests that falcons continue to be exposed to environmental contaminants.

To determine factors responsible for low productivity of ospreys (Pandion haliaetus) nesting along Delaware Bay, we compared their reproductive success to birds nesting along the Atlantic Coast during 1987 and 1988. Productivity of ospreys nesting along Delaware Bay was lower because 50% of all nests initiated failed, whereas only 21% of Atlantic Coast nests failed. Only 50% of all eggs laid in the Bay colony hatched, compared to 69% in the Atlantic Coast colony. Nestling mortality was similar between colonies (26 vs. 18% for Delaware Bay and Atlantic Coast, respectively) but 21% of those young hatched near the Bay were probably preyed upon by great horned owls (Bubo virginianus). Although Delaware Bay ospreys spent considerably more time away from their nests, presumably foraging, than did Atlantic Coast birds, adults from both colonies spent similar amounts of time feeding young, which suggests that food stress did not influence productivity. High frequency of unhatched eggs and thinner eggshells (8% below pre-DDT levels vs. 3% for Atlantic Coast eggs) of ospreys along Delaware Bay suggests possible exposure to environmental contaminants that may reduce hatching success.

The movements and distribution of 65 radio tagged red knots on Delaware Bay from May to June 2004 and related movements to the distribution and abundance of horseshoe crab eggs and to other habitat characteristics are studied. The findings are found to be consistent with the hypothesis that the abundance of horseshoe crab eggs on sandy beaches is driving movement and distribution of red knots and that there is little alternative food during the majority stopover in Delaware Bay.