Seasonal and diurnal mass variation in Black-capped Chickadees and White-throated Sparrows

摘要

During the winters of 1989-90 and 1990-91, we recorded mass of free-ranging Black-capped Chickadees (Parus atricapillus) and White-throated Sparrows (Zonotrichia albicollis) in northern New Jersey. The data presented here are the first records of seasonal and diurnal mass variation for untrapped passerines in North America. Previous studies have shown that captivity and handling can significantly bias results of studies of avian mass (King and Farner 1966, Castro et al. 1991, Refsnider 1993). Study area and methods.-We recorded mass of Black-capped Chickadees in Mendham, New Jersey (40°46′N, 74°32'W) from November 1990 through March 1991. We weighed White-throated Sparrows from January through March in 1990 and 1991. The study site was in a residential suburban neighborhood containing several feeders. Local weather conditions during the two winters of observation were milder than usual with less than normal precipitation (National Climatic Data Center 1989-91).