Co-roosting within an enclosed space: are Chimney Swifts (Chaetura pelagica) disturbed by sharing a roost chimney with Rock Pigeons (Columba livia)

Abstract

Many avian species co-roost with other avian species, but roost sharing has not previously been reported for species that roost in enclosed spaces. We report co-roosting of Chimney Swifts ( Chaetura pelagica (Linnaeus, 1758)) and Rock Pigeons ( Columba livia J.F. Gmelin, 1789) in a Sault Ste Marie, Ontario, Canada, chimney. We predicted that life history and behavioural differences between the two species would lead to disturbance in Chimney Swifts, but not Pigeons. Of two chimneys examined, Swifts exited earlier in the morning in the chimney with co-roosting than in the chimney where they roosted alone. While Pigeons appeared undisturbed by moving Swifts unless Swifts landed on them, Swifts were sensitive to Pigeon activity. In the evening, Pigeon movements caused Swifts to relocate within the chimney or to exit the chimney. Not all departed Swifts re-entered the roost following the disturbance. In the morning, Swifts appeared more tolerant of Pigeon movement, but were often disturbed by Pigeon exit or entry. Permanently exiting the roost in the evening or departing too early in the morning may increase energy expenditure costs for migrating Swifts. Installing Pigeon deterrent devices at the chimney may reduce disturbance to Chimney Swifts within the roost and potentially prevent early exit in the morning.