Time-budgeting by starlings Sturnus vulgaris: Time minimizing, energy maximizing and the annual cycle organization

Summary

In seasonal environments, time often constrains the timing and duration of processes in annual cycles of animals both on the diel and annual basis. Therefore, the allocation of time e.g. to foraging, resting and breeding behaviours should be true adaptations to the particular circumstances the animals experience.

In the present study, time budgets were established for two North Scandinavian starling (Sturnus vulgaris) populations (Andøya, Norway and Umeå, Sweden) with fundamentally different annual cycles. The major components of the time budgets of both populations were foraging and resting. There was also a pronounced seasonal shift in the relationship between these activities. As expected, starlings from both populations increased foraging time during the breeding period. However, contrary to the predictions foraging time was shortest in mid-winter for the sedentary northernmost population at Andøya. Moreover, females from both populations generally allocated more time to foraging than males.

These findings are discussed in relation to the energy maximizing-time minimizing concept. It is concluded that these foraging strategies are not as generally valid as previously assumed, especially not in highly seasonal environments.