Changes in Behavioral Time Allocation of Waterbirds in Wing-Molt at Lake Constance

Abstract

The reduced mobility of flightless waterbirds during wing-feather molt should influence time allocation during the day, but time-budget studies are lacking in most species. Here, time budgets of flightless and fully-winged individuals at Lake Constance, Central Europe, were compared for five waterbird species with different feeding ecology and varying sensitivity to disturbances or predation pressure. Significant differences in diurnal activity budgets of flightless and fully-winged birds were observed in all five species. Different behaviors were responsible for the observed differences. Flightless Mute Swans Cygnus olor spent more time feeding while decreasing locomotory activity. Red-crested Pochard Netta rufina also increased feeding, but, in addition, had increased locomotory activity while resting less. In contrast, flightless individuals of both Gadwall Anas strepera and Tufted Ducks Aythya fuligula spent less time foraging, while there was no such change in Eurasian Coot Fulica atra. More consistent patterns were observed in vigilance behavior, which increased in three of the five species. Comfort activities, such as preening, increased in two species, and were unchanged in the remaining three. Social interactions, which constituted only a small part of the daily budget, only changed in Gadwall. The present data suggest that the five waterbird species meet the increased energy demands during molt by either one or a combination of behavioral adaptations, i.e. different strategies, such as higher nutrient intake (e.g. Mute Swan, Red-crested Pochard), lower energy consumption by reducing the locomotory component (e.g. Mute Swan, Tufted Duck) or a breakdown of energy reserves deposited prior to the molting period resulting in more time spent resting (e.g. Gadwall). Also, increased resting times during the day may indicate nocturnal feeding, which needs to be examined in more detail.