This study examines prey availability as a factor influencing breeding habitat selection by Kirtland's Warblers (Dendroica kirtlandii), and characterizes the foraging behavior of this endangered species. Kirtland's Warblers nest on the ground in early-successional jack pine forests in northern Lower Michigan. The species may reject old jack pine stands for nesting due to decreased prey density in lower branches and ground vegetation of old stands. Insects were captured in young and old nesting habitat and in mature jack pine too old to be attractive for breeding, and birds were observed foraging in young and old nesting habitat. Insect biomass in low vegetation was less in old nesting habitat than in young nesting habitat, and was much less in mature habitat. Kirtland's Warblers in old nesting habitat did not forage higher than those in young nesting habitat, suggesting that the decrease in insect biomass in old nesting habitat is not great enough to affect the birds. Managed plantations and natural wildfire-regenerated jack pine stands were very similar in terms of insect abundance, diversity, and distribution, and warbler behavior. Warblers foraged most often on jack pines, but also used ground vegetation and pin oak trees as foraging substrates. The proportion of foraging attempts in oak varied widely among stands, suggesting that warblers use oak in proportion to its availability. Female Kirtland's Warblers foraged significantly lower than males, following a general trend for species of parulid warblers.