Impact of nesting microhabitat and foraging habitat on the nesting site selection of the northern black swift (cypseloides niger borealis)

The northern black swift (Cypseloides niger borealis) is an insectivorous bird that nests in small colonies in western North America. The black swift is a California Species of Special Concern with a statewide population estimate of 200 pairs. Previous research has mostly focused on nesting locations, whereas foraging habitat is largely unresearched due to the difficulty of detecting foraging black swifts. We conducted surveys for black swifts in the southern Sierra Nevada. We collected data from 67 potential nesting sites on six aspects of black swift nesting microhabitat: water flow, vertical relief, aerial access, shade, nesting niches, and moss cover. We collected additional data from surveys in Colorado for a total of 109 observations in California, Colorado, and New Mexico. We used the proportion of standing water and wetlands within four concentric rings extending from each colony as an index of foraging habitat quality. Water and wetlands are a major source of emergent insect prey. These scores were used as independent variables to determine their relative effect on the occurrence of black swifts at each site. We located a total of nine black swift colonies in California, three of which were previously unknown. Our results indicate that foraging habitat is a more influential driver of nesting site selection than microhabitat and water was the most significant subcomponent of microhabitat. We exercise caution in our interpretations due to our small sample sizes.