Defence of offspring by male swallows, Hirundo rustica, in relation to participation in extra-pair copulations by their mates

Abstract

Defence of offspring by male swallows against a stuffed little owl, Athene noctua, predator model was studied in relation to participation of the mate in extra-pair copulations. The frequency of extra-pair copulations was manipulated by temporarily detaining males during the fertile period of their mates. Experimental colonial females experienced more extra-pair copulations than control colonial ones. Detained males defended their offspring less intensely, staying away from the predator model, giving fewer alarm calls and spending less time near the predator than did their mates. Solitarily breeding experimental females did not experience more extra-pair copulations than did their controls. Temporary detention of a group of colonial males during the incubation period of their mates did not reduce the intensity of their brood defence compared to control males, suggesting that detention per se did not have a negative effect on brood defence. The frequency of extra-pair copulations, and therefore presumably certainty of paternity, thus affects amount of, and sex roles in, anti-predator defence.