Incubation routine, duration of foraging trips and regulation of body mass in Short-tailed Shearwaters (Ardenna tenuirostris)

Abstract

The energy demands of incubation can present important costs in avian reproduction. In species where incubation is shared, the time that individuals have for foraging may be influenced by their own foraging success and their partner's ability to fast while incubating. To investigate the costs of incubation, 60 pairs of Short-tailed Shearwaters (Ardenna tenuirostris) were studied on Great Dog Island, Tasmania, to determine ifbody mass influences incubation routines, duration of foraging trips and neglect of eggs. Body mass throughout the incubation period varied considerably, with birds losing an average of 20% of their original body mass as a result of complete fasting while on land. Initial body mass of males was positively correlated with time spent incubating, and heavier birds had the ability to extend their incubation shift if their partner was delayed or failed to return from sea. The body mass when birds left the nest to return to sea was associated with days spent foraging, and was inversely related to the mass gained at sea. Temporary egg neglect was observed in both successful and unsuccessful breeding attempts, but increased the risk of breeding failure. No specific mass threshold at which birds left the nest if not relieved by their partner could be determined. Avian reproduction represents a trade-off in use of resources between current survival and reproductive investment. The results suggest that body mass during incubation plays an important role in the reproductive behaviour of Short-tailed Shearwaters, enabling adults to regulate the trade-off between risks of adult mortality and breeding failure.

Additional keywords:

• egg neglect
• incubation costs
• marine ecology
• Procellariiformes
• seabird ecology