Brood territories in buffleheads: determinants and correlates of territory size

Abstract

In most species of ducks, only females tend the brood, and they do not defend brood territories. However, in buffleheads (Bucephala albeola), females strongly defend brood territories. I examined factors affecting territory size of broods, and their consequences for growth rate and survival of ducklings. Brood density tended to be higher on ponds with higher food density. Territory size was inversely correlated with both food abundance in the territory and brood density on the pond. The slope of the relationship between territory size and food did not differ significantly from −1, the slope expected if females adjust territory size to maintain a constant food supply. Partial correlation analysis, however, revealed that brood density may be a more important proximate determinant of territory size than food. Growth rates of ducklings were not affected by food density but were depressed at high brood density in one year. Duckling survival increased with food density in the first year but was depressed at high brood density in the next. I suggest that females select a brood territory and that the size of that territory varies according to both food and brood density. This apparently buffers the effects of variation in food and brood density on growth and survival of ducklings.