The Effects of Food Supplementation on Extraterritorial Behavior in Female Northern Cardinals

We tested how food supplementation affects extraterritorial behavior in the socially monogamous Northern Cardinal (Cardinalis cardinalis). Assuming extraterritorial movements are energetically costly, we predicted that if these movements function for gaining extra-pair matings, females on supplemented territories would spend more time off territory, make more extraterritorial forays, and have larger home ranges in relation to territory size than those on unsupplemented territories. If extraterritorial movements function for foraging purposes, then supplemented females should spend less time off territory, make fewer forays, and have smaller home ranges than unsupplemented females as a result of plentiful food on their home territories. We radio-tracked seven females during their fertile periods and found a trend for supplemented females to make more extraterritorial forays and spend more time off territory than unsupplemented females; however, there was no significant difference in home range sizes between treatment groups. Our findings provide some support for the extra-pair copulation function of extraterritorial movements in female Northern Cardinals.