Delaware Bay is an important spring stopover site for the Western Atlantic Red Knot (Calidris canutus rufa), which has suffered a recent population decline. Stable-isotope evidence suggests Red Knots from different wintering areas partially segregate at the site, with short-distance migrants concentrating on the Atlantic coast of New Jersey rather than in Delaware Bay itself. The Red Knot has been little studied on the Atlantic coast, and our objectives were to determine the extent to which birds captured on the coast used Delaware Bay and to characterize their habitat use and behavior. In 2006, we radio-tracked birds captured on an Atlantic beach and collected behavioral data and prey samples for comparison to those at randomly selected plots within Red Knot habitat. Depending on tidal stage, the distribution of Red Knot locations was skewed toward either Atlantic marshes or beaches. It was skewed away from Delaware Bay on the falling tide. Red Knots observed in Delaware Bay were foraging, whereas birds on the Atlantic coast were equally likely to forage or rest on rising and high tides. On the Atlantic coast, Red Knot locations had significantly more prey items than did random points, but this was not so on Delaware Bay beaches. Our results support the idea of partial segregation between Red Knots stopping on New Jersey's Atlantic coast and those in Delaware Bay, at least in some years. Whatever the cause of this partial segregation, conservation of Red Knots depends on protecting a complex of stopover habitats.
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