Mate guarding and copulation behaviour in monogamous and polygynous blue tits: do males follow a best-of-a-bad-job strategy?

This study investigates the importance of mate guarding for males and females in the facultatively polygynous blue tit Parus caeruleus. We present observational data in combination with a paternity analysis using DNA fingerprinting to show that (1) male blue tits guard their mate, since they stay closer to their mate, initiate fewer flights and follow their mate more often during the female's presumed fertile period; (2) polygynous males do not suffer more from lost paternity despite lower mate guarding; (3) in monogamous pairs there is either no relation or a positive relation (depending upon the variable measured) between measures of mate guarding intensity and the proportion of extra-pair young in the nest; and (4) monogamous males that are more often followed by their fertile female suffered less from lost paternity. We conclude that, despite mate guarding, paternity seems to be largely under female control and unattractive males guarding their mate are making the best of a bad situation. Experimental evidence is provided showing that when males were temporarily removed from their territory, their mate suffered from increased harassment from neighbouring males that intruded in the territory and tried to copulate with the female. Almost all of these copulation attempts were unsuccessful because females refused to copulate. We conclude that mate guarding may be beneficial for females because harassment by neigbouring males is prevented.