Do males of the great grey shrike, Lanius excubitor, trade food for extrapair copulations?

In several animal species, males offer material gifts to females during a courtship or precopulatory display. The provision of nutrients is a male investment that can increase female reproductive success; therefore males can use such gifts to influence female choice. Clear examples of courtship feeding before extrapair copulations are scarce, however. We investigated courtship feeding in the great grey shrike. Males offered food both to their mate and to extrapair females. Food offered to extrapair females had a significantly higher energy value than that offered to the social mates. The size of prey offered may enable females to judge a male's quality. A larger gift resulted in a higher chance of copulation for males in both within- and extrapair events. We conclude that the energy value of nuptial gifts can explain why females of some species engage in extrapair copulations.