Prevalence of Disjunct Roosting in Nesting Bank Swallows (Riparia riparia)

Bank Swallows (Riparia riparia) congregate in large nocturnal roosts during the non-breeding season. Scant evidence suggests that Bank Swallows may also congregate regularly in nocturnal roosts during the breeding period. To help clarify the issue, we used automated radio-telemetry to document the roosting behavior of 11 males and 11 females that were tending nests with young at two nesting colonies. Nineteen of the 22 birds (86%) spent at least one night roosting away from the colony, and 13 of the 22 birds (59%) spent at least one night roosting likely within a large marsh located similar to 30 km away from the colonies. Females tended to roost overnight at the colony more than males. The proportion of nights birds spent roosting away from the colony was highly variable between individuals. Minimum flight speeds to an evening roost site (similar to 30 km distant) were significantly greater than return flights back to the colony in the morning. Our study confirms that breeding Bank Swallows do in fact regularly roost away from the colony during the nestling period. Our study also highlights some new and intriguing questions regarding how Bank Swallows use the landscape during the breeding season, and the potential importance of wetland roost sites in the proximity of breeding colonies.