Nest location and feeding energetics of ruby-throated hummingbirds (Archilocus colubris) were examined in northern Michigan. The hummingbirds fed on tree 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 six nests studied were within 300 m of a sapsucker feeding tree. Laboratory studies indicated that the birds could be fully supported by the feeding trees, which contained phloem sap at a concentration of 16 g sugar per 100 g solution (0.47 M sucrose equivalent). In northern Michigan, ruby-throated hummingbirds were energetically coupled to the feeding trees of sapsuckers and thus achieved reduced energy costs in this northern climate.