Reduction in escape performance as a cost of reproduction in gravid starlings, Sturnus vulgaris

Predation is known to be an important cost of reproduction in shaping the evolution of avian life-histories. However, published work has concentrated on behaviours associated with reproduction that incur an increase in predation risk. Relatively little attention has been given to the effect of reproduction on the ability to escape predators, once an attack has been launched. Body mass increases markedly before and during egg laying in female birds and there is good evidence, both theoretical and empirical, that increases in mass have a detrimental effect on flight performance. On attack, initial take-off performance is critical in determining the probability of escape from aerial or ground predators. Escape performance was assessed in female European starlings (Sturnus vulgaris) for 6 weeks of the breeding season, with respect to speed and angle of ascent during take-off. Repeated measures on the same individuals show that angle of ascent during take-off decreases before and during laying. Speed of take-off was inversely correlated with body mass within individuals. This decreased take-off ability, and hence ability to escape a predator, may be an important and previously ignored cost of reproduction in birds.