Loss of nesting sites is not a primary factor limiting northern Chimney Swift populations

Abstract

Aerially-foraging insectivorous bird populations have been declining for several decades in North America and habitat loss is hypothesized as a leading cause for the declines. Chimney Swifts (Chaetura pelagica) are a model species to test this hypothesis because nest site use and availability is easily assessed. To determine if nest site availability is a limiting factor for Chimney Swifts, we established a volunteer-based survey to inventory and describe chimneys (n = 928) that were used or unused by swifts. A logistic regression model showed that swifts preferred chimneys with a greater length exposed above the roofline and greater inside area, which were not associated with residential buildings. The average chimney used by swifts extended 2.86 m above the roofline with an internal area of 10,079 cm 2 . The regression model represents the range of nest-site conditions that swifts will tolerate; this was used to build a linear discriminant function (ldf) that had an I-index of 82 % (measure of prediction success). We applied the ldf coefficients to predict chimney occupancy in three southern Ontario communities. Of 366 open chimneys, the ldf classified 139 as suitable but only 24.4 % were occupied by swifts. Given that[75 % of suitable sites were unoccupied, swifts are likely not experiencing competition from habitat saturation. Our results suggest that Chimney Swift populations, and likely other aerially-foraging insectivorous birds, are limited primarily by other processes not measured in this study, such as changes in prey.

Differences in spatial synchrony and interspecific concordance inform guild‐level population trends for aerial insectivorous birds

“…e). Chimney swifts occasionally roost within natural tree cavities (Zanchetta et al ), but prefer large industrial chimneys that extend far above rooflines (Fitzgerald et al ). Chimney availability does not appear to be limiting chimney swift populations in Ontario, where only 24% of suitable chimneys are occupied (Fitzgerald et al ).…”

High ambient temperatures induce aggregations of chimney swifts Chaetura pelagica inside a roost

“…Model -0.029 ± 0.003 -9.686 < 0.001* chimneys that extended higher above rooflines providing a larger area to be heated (Fitzgerald et al 2014). To our knowledge, no other study has examined roosting direction preference; however, our findings are similar to studies of other cavity users, such as tree swallows (Rendell andRobertson 1994, Ardia et al 2006), woodpeckers (Inouye 1976), and big brown bats (Kalcounis and Brigham 1998), that have been observed to show a preference for cavities with south-facing entrances, which have been shown to be warmer (Wiebe 2001).…”

Loss and Preservation of Chimney Swift Habitat in Manitoba, 2007-2016

“…However, Fitzgerald et al noted that over 75% of potentially suitable Chimney Swift sites were not occupied in southern ontario. 3 of the 191 chimneys monitored by mCSi, 57 (29.8%) have not been seen to house Chimney Swifts (sampling rate is 13.7% of 519 chimney-years, adjusted for lost chimneys). moreover, three large roost sites in manitoba have housed large numbers of Chimney Swifts after nesting had started.…”

“…2 SArA lists loss of nesting and roosting habitat (chimneys) as the most significant threat although Fitzgerald et al suggest chimney habitat in ontario may not be a limiting factor. 3 There seem to be few data on the rate at which chimneys suitable for Chimney Swifts are being lost from their environment and whether such losses are limiting or not. using data collected by volunteer citizenscientists in manitoba, it is now possible to estimate the annual rate at which available chimney habitat is being lost in this part of the bird's range.…”