Problems associated with pooling mark-recapture data prior to estimating stopover length for migratory passerines
This article is part of a larger document. View the larger document here.Abstract
One measure of the importance of a stopover site is the length of time that migrants spend at an area, however measuring the time birds spend at a stopover site has proven difficult. Most banding studies have presented only minimum length of stopover, based on the difference between initial capture and final recapture of birds that are captured more than once. Cormack-Jolly-Seber (CJS) models have used multiple recaptures to estimate stopover length by migrants, and recently a new model (Stopover Duration Analysis, SODA) incorporating recruitment estimates has been suggested. Using banding data from Red-eyed Vireos (Vireo olivaceous), American Redstarts (Setophaga ruticilla), and Northern Waterthrushes (Seiurus noveboracensis) captured during fall migration on Appledore Island, Maine, during 1999 and 2000, we evaluated stopover estimates from minimum stopover and SODA methods. In particular, we investigated the effects of pooling data for analysis on stopover estimates. Results from our banding data and model simulations suggest that pooling may result in biased stopover estimates, by increasing estimates with increased pooling interval sizes. Furthermore, pooling may also increase the variance in the estimate. Thus pooling should be used with caution and avoided when possible.