Trade-offs in activity budget in an alpine ungulate: contrasting lactating and nonlactating females

Abstract

Optimal time allocation to foraging behaviour may be constrained by intrinsic and extrinsic factors forcing animals to adopt compromises to meet their daily energetic needs. Our goal was to assess the influence of individual characteristics and extrinsic factors on the activity budget of marked adult female mountain goats, Oreamnos americanus. As lactation entails important energetic costs, we specifically aimed at contrasting activity budgets of lactating and nonlactating females. We determined female activity budgets using 10-min interval scan sampling between 2002 and 2005. Lactating females, females raising sons and females that were subordinate for their age spent more time foraging than nonlactating females, females raising daughters and dominant females, respectively. Although foraging is typically incompatible with scanning, increased time spent foraging was mainly performed at the expense of time spent lying rather than time spent in vigilance. Lactating females also increased time spent ruminating while lying compared with nonlactating females. All females traded lying time for increased foraging and ruminating times in early and late summer. Females spent less time foraging on warm days, and foraged more at dusk than during the rest of the day. Age and body mass did not influence female activity budgets. Our results indicate that lactating females partly compensated for the costs of lactation by trading lying for foraging time, and reorganized lying time to increase the proportion of time spent ruminating. This study emphasizes the fundamental behavioural trade-offs that female mammals must face to meet their daily energetic requirements and allows a better understanding of how these compromises vary through the lactation period.