Energetics of Feeding on Tree Sap by Ruby-Throated Hummingbirds in Michigan

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Abstract
Nest location and feeding energetics of ruby-throated hummingbirds (A. colubris) were examined in northern Michigan. The hummingbirds fed on tree [usually Betula papyrifera] phloem sap made available by holes drilled by yellow-bellied sapsuckers (Sphyrapicus varius). During the nesting season females were specialists, feeding almost exclusively on tree sap and rarely taking flower nectar. All 6 nests studied were within 300 m of a sapsucker feeding tree. The birds could be fully supported by the feeding trees, which contained phloem sap at a concentration of 16 g sugar/100 g solution (0.47 M sucrose equivalent). In northern Michigan, ruby-throated hummingbirds were energetically coupled to the feeding trees of sapsuckers and achieved reduced energy costs in this northern climate.