Physiological Evidence That Anthropogenic Woodlots Can Substitute for Native Riparian Woodlands as Stopover Habitat for Migrant Birds

The ability to find sufficient high-quality stopover habitat is a crucial factor for successful migration for woodland migrant birds. Woodland habitats are scarce in the Northern Prairie region of North America, and natural woodlands have been greatly reduced concurrent with the appearance of small anthropogenic woodlands on the landscape. Landbird migrants use both natural and anthropogenic woodlands in this region as stopover habitats, but the relative quality of these two habitats is unknown. We assessed the relative habitat quality of the two habitats by comparing body mass (M-b) and plasma metabolites associated with fattening (triglycerides [TRIG]) or fat catabolism (-hydroxybutyrate [BUTY], glycerol [GLYC]) in individual species, taxa, and foraging guilds of migrating woodland birds during both spring and fall migrations. The only significant difference in M-b between birds in the two habitats occurred for fall yellow-rumped warblers (Setophaga coronata), where M-b was 8% greater in corridors than in woodlots. No significant between-habitat differences occurred for plasma TRIG at either season. Significant between-habitat differences for plasma BUTY occurred only for ruby-crowned kinglets (Regulus calendula; 61% higher in corridors) in fall. Plasma GLYC differed significantly between habitats for a few groups, including vireos (190% higher in woodlots), warbling vireos (Vireo gilvus; 263% higher in woodlots), and Nashville warblers (Oreothlypis ruficapilla; 226% higher in woodlots) in fall. The few significant differences and absence of a consistent direction of variation in M-b and plasma metabolites suggests similar stopover habitat quality in these two habitat types. Thus, during migration through the Northern Prairie region anthropogenic woodlots can, at least partially, substitute as stopover habitat for lost and degraded native riparian habitats for woodland birds.