Cross-seasonal effects in the American Woodcock: Conditions prior to fall migration relate to migration strategy and implications for conservation

Abstract

ABSTRACT How postbreeding habitat quality and body composition of migratory birds carry over to influence fall migration strategies and residency merits consideration when creating cross-seasonal conservation plans, especially in breeding populations that are partial migrants. We assessed the influence of postbreeding habitat quality on departure body composition and fall migration patterns in a southern New England breeding population of American Woodcock (Scolopax minor). Woodcock that overwintered near breeding areas (n = 5) had less fat upon capture in fall and used lower quality habitat during the fall than birds that eventually departed on migration (n = 17). Woodcock that departed earlier were long-distance migrants that had inhabited higher quality landscapes prior to migration, departed with less or similar fat stores, stopped over for shorter periods on migration, and arrived earlier on their more southerly wintering areas. In contrast, woodcock that departed later were short-distance migrants that had inhabited lower quality landscapes prior to migration yet stored similar or more fat upon departure, stopped over for longer periods on migration, and arrived relatively late to their more northerly wintering areas. These differences in migration strategies were evident under the same fall environmental conditions and did not appear related to individuals responding to their own condition as would be expected if they were classic condition-based carry-over effects. As such, the southern New England breeding population of woodcock is best categorized as nonfacultative partial migrants (i.e., includes residents, short-distance migrants, and long-distance migrants) that demonstrate weak connectivity between life stages; such populations are excellent for the study of the costs and benefits of migration. The stopover and wintering areas used by woodcock in the coastal mid-Atlantic states deserve conservation and management attention in order to preserve critical habitat throughout their wintering range. LAY SUMMARY Effective conservation of migratory birds requires knowing how conditions prior to migration relate to the timing, routes, and destinations of birds during migration. We used VHF radiotelemetry to track American Woodcock (Scolopax minor) in southern New England throughout the summer and fall, recaught them prior to fall migration and used the deuterium-dilution method to nondestructively estimate their departure body composition, and then used GPS radiotelemetry to track them every few days throughout fall migration until they reached their wintering areas. At the time of fall migration, resident woodcocks were less fat than individuals that eventually migrated. Migratory woodcock that inhabited higher quality landscapes in the fall departed earlier and, with less or similar fat stores, stopped over for shorter periods on migration, and arrived earlier on their more southerly wintering areas than birds that inhabited lower quality landscapes. However, if we assume fattening rates were maximal for woodcock inhabiting higher quality landscapes, then departure fat of woodcock was similar in different quality landscapes. Given that this southern New England breeding population of woodcock included residents that overwintered as well as short- and long-distance migrants, these woodcock are best categorized as nonfacultative partial migrants. To preserve such variation in migratory strategies requires conserving key stopover and overwintering areas in the coastal mid-Atlantic and southeastern United States.