Deceptive use of alarm calls by male swallows, Hirundo rustica: a new paternity guard

Abstract

Male swallows (Hirundo rustica) frequently gave alarm calls when their fertile mates left the nest vicinity without the male during egg laying. Females engaged in extrapair copulations during such absences when they were not guarded intensely by their mates. However, males were sometimes able to disrupt extrapair copulation attempts toward their mates by giving alarm calls, causing all nearby swallows to take flight. I experimentally tested the idea that male swallows gave alarm calls when their certainty of paternity was at stake. When colonially breeding female swallows were temporarily chased away from their nest during the egglaying period in the absence of their mates, males nearly always gave alarm calls when they returned to the empty nest. In contrast, colonially breeding males rarely gave alarm calls when their mates were absent during the prelaying or the incubation periods. Solitarily breeding males rarely gave alarm calls in the absence of their mates, irrespective of the time in their nesting cycle. However, solitarily breeding males did give alarm calls when their mates were absent from the nest if a male mount previously had been presented near their nest during the egg-laying and the prelaying periods, but not during the incubation period. Deceptive use of alarm calls (in the absence of any predators) by male swallows apparently was an effective paternity guard.