Seasonal Patterns of Fat Deposits in Relation to Migratory Strategy in Facultative Migrants

Physiological preparations for migration generally reflect migratory strategy. Migrant birds fuel long-distance flight primarily with lipids, but carrying excess is costly; thus, the amount of fat deposited prior to departure often reflects anticipated duration or distance between refueling bouts. Seasonal pre-migratory deposition well documented in regular seasonal migrants, less described more facultative species. We analyze deposits free-living across several taxa migrants songbird subfamily Carduelinae, including house finches ( Haemorhous mexicanus ), American goldfinches Spinus tristis pine siskins pinus ) and four different North ecotypes red crossbills Loxia curvirostra evaluate during periods. Our data suggest that extent corresponds tendency these taxa. Specifically, nomadic a seasonally predictable annual movement demonstrated relatively large coincident In contrast, siskins, thought be variable timing initiation movements, had smaller peaks season, partial migrant goldfinch resident finch showed no Within crossbills, those are closely associated habitats larger autumn periods higher wing loading, whereas spruces, Douglas-fir hemlocks spring lower loading. conclude population averages do strategies species, as winter thermogenic challenges at study locations. A difference fattening loading among crossbill consistent possibility they differ their biology, we discuss differences light reproductive schedules phenologies conifer