Mass change during migration stopover: A comparison of species groups and sites

Hourly mass gain during migratory stopover in spring and fall was estimated for 48 species at three sites on Long Point, Ontario. Estimates were based on regression of size corrected mass at first capture on time of day. Mean mass gain for all species and sites in fall was 0.61% of lean body mass/h, well over the mean estimated gain required to maintain daily energy balanc e (0.27% of lean body mass/h). In spring, mass gain was 0.50% of lean body mass/h at two sites but only 0.17% at the extreme tip of Long Point, where cold lake temperature in spring probably affects insect abundance. While mo st species fared well in fall, thrushes did not, perhaps due to poor habita t for ground foraging on Long Point. Except for the eastern tip of Long Poi nt in spring, the study sites compare favorably in mass gain to two other s tations in the northern U.S. where similar analyses have been done.