Division of labour in breeding Trumpeter Swans Cygnus buccinator

Abstract

We used time budget analysis to quantify and compare breeding behavior of male and female Trumpeter Swans nesting in Alaska (1988 and 1989) and in Idaho and Wyoming (1991). Females fed more than males during the prelaying/laying period while males provided the bulk of nest construction. Males spent more time at the nest during female incubation recesses and less time at the nest when females were incubating. Males were more alert and aggressive when incubating females left the nest, and they fed and slept less. Male nest-sitting, previously undescribed for wild Trumpeter Swans, was a regular behavior for some males. All males were more active than females in repelling predators, and males were more aggressive toward other swans and geese. Male specialization in performing these duties probably enables females to accumulate or replenish nutrient and energy reserves more effectively and ultimately enhances the reproductive success of the pair.