TURNOVER RATES OF FALL-MIGRATING PECTORAL SANDPIPERS IN THE LOWER MISSISSIPPI ALLUVIAL VALLEY

Abstract

Knowledge of the length of time spent at migratory stopover sites, or stopover duration, can help biologists estimate the total number of birds passing through a site, which in turn can be used to estimate population size. We estimated the stopover duration for 106 radiomarked pectoral sandpipers (Calidris melanotos) in the Lower Mississippi River Alluvial Valley (MAV) during fall migrations in 2001 and 2002. We estimated time-at-site-after-capture by tracking radiomarked birds daily to determine their time of departure from stopover sites. We used length-biased sampling and program DISTANCE to estimate stopover duration from time-at-site-after-capture. Our estimate of stopover duration for pectoral sandpipers in the MAV over all sites and both years was 10.0 days (95% CI = 8.2–11.7). Aerial telemetry relocations from 2002 indicated that many pectoral sandpipers used multiple stopover sites during their migration through the MAV, which suggested that the total time spent by pectoral sandpipers in the MAV during fall migration, or turnover rate, was longer than the stopover duration. Future research should focus on estimating the number of stopover sites used by pectoral sandpipers and determine whether other shore-bird species use multiple sites as well. If shorebirds migrating through the MAV stay in the region for a period longer than the 10 days suggested by the Lower Mississippi Valley Joint Venture (LMVJV) Migratory Bird Science Team in their modeling of shorebird energetic requirements, then more habitat may be required by shorebirds during fall migration than the 2,000 ha the group calculated for the MAV.