Staging Behavior in Red Knot (<i>Calidris canutus</i>) in Delaware Bay: Implications for Monitoring Mass and Population Size

Abstract

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 , 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 days, which declined to 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 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 of , Red Knot that arrived at an average mass of g and, on average, gained mass at . g day . Thus, in , the passage population was substantially smaller than the recent peak count of , in , 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.