Aspects of Municipalities Associated with Occupancy and Abundance of Chimney Swifts in Illinois

The Chimney Swift (Chaetura pelagica) is a bird species of conservation concern in Illinois and one of many aerial insectivores experiencing population declines across North America. While causes of declines are unknown, habitat availability and changes in insect populations are likely contributing factors. Chimney Swifts historically nested in tree cavities, but switched to nesting primarily in masonry chimneys as North American settlements expanded. With the growing trends of chimney caps and gas/electric heating, available chimneys are disappearing, and the loss of available nest sites may be driving Chimney Swift declines. Like other aerial insectivores, Chimney Swifts may also provide valuable pest control services and action may be needed to maintain this benefit. To investigate potential causes of declines in Illinois, we examined the influence of habitat and landscape factors on Chimney Swift abundance. We conducted surveys for swifts in 126 municipalities throughout Illinois and recorded the number of uncapped masonry chimneys at each survey point. We used these data along with landscape-level data such as composition of land cover surrounding points, areal extent of municipality, and age distribution of buildings. We found that 97% of municipalities were occupied by Chimney Swifts, but abundance varied considerably. Swifts were detected at 72.5% of survey points. Chimney Swift abundance was most heavily influenced by the number of uncapped masonry chimneys at survey points. Our results suggest that although Chimney Swifts are still widespread, contemporary building practices will continue to drive population declines and management should focus on approaches for providing and preserving suitable nesting sites.