Consequences for Carolina Chickadees of Foraging with Tufted Titmice in Winter

The purpose of this investigation was to accomplish a simultaneous evaluation of both the costs and benefits of mixed—species foraging for a socially subordinate species. Specifically, we studied Carolina Chickadees that commonly forage in winter with a socially dominant congener, the Tufted Titmouse. We prevented these species from foraging together by removing titmice from five central Ohio woodlots. We then compared the biology of chickadees on these sites to that of chickadees on four sites where titmice had not been removed. Where titmice had been removed, chickadees foraged in more titmouse—like locations. Although this shift was statistically significant for two of the five niche parameters measured, there was a consistent pattern of shifts toward the titmouse niche in all five. We were unable to detect a change in chickadee vigilance in the absence of titmice. Chickadees showed statistically greater induced feather growth in the absence of titmice, indicating better nutritional condition, but we detected no differences in survival between treatment groups. We conclude that the foraging niche results provide evidence of a cost to chickadees of foraging with titmice. Furthermore, based on the feather growth results, we conclude that the costs and benefits for chickadees of this interaction sum to a net cost in foraging efficiency if not in survivorship.