Pre-laying time budgets in rock pipits: priority rules of males and females

Abstract

Theory suggests that males should invest heavily in mating effort, while females usually gain little from multiple matings. Males should also minimize foraging, but invest heavily in territory defence and mate guarding, whereas females should focus on gathering nutrients and energy in order to increase brood size and quality. In this study these ideas were tested using time-budget data from rock pipits, Anthus spinoletta, collected during the pre-laying season in 2 years. Foraging and perching were the two most common activities, together making up more than 75% of the time budget of both sexes. As predicted, females foraged more often than males, while males spent more time surveying the territory from perches on elevated look-out posts; males also tended to fly more, and interacted more frequently with other pipits. Foraging time of individual birds was inversely related to perching time in both sexes. Females foraging less spent more time preening. Males that were foraging often seemed to maintain vigilance, in spite of their shorter perching time, by scanning frequently during foraging bouts. Males lost weight throughout the pre-laying season; in contrast, females increased considerably in weight prior to laying. Perching time increased during the pre-laying season in both males and females. Foraging birds of both sexes were apparently more vigilant early during pair formation, since time used for scanning declined nearer laying in spite of unchanged foraging time. Males perched more and performed song-flights more frequently in the morning, while they increased their feeding rate the day. These behavioural patterns suggest that females emphasized feeding more than males, and that territory surveillance and alertness of potential mates was given high priority by males, especially during morning hours and early in the season. Some explanations for the behavioural differences between the sexes are discussed.