Patterns of food allocation between parent and young under differing weather conditions in the Common Swift  (Apus apus)

MARTINS T.L.F. and WRIGHT J.

23 81
Read Article     Download


Abstract:

Brood sizes were manipulated to promote different levels of parental effort in the Common Swift (Apus apus). The two years in which these brood size manipulations were carried out differed with regard to weather conditions, Data were collected on a visit by visit basis to reveal changes in parental and chick body rnass, the mass of prey delivered and the estimated mass of parental self-feeding. This provided a powerful method for testing hypotheses regarding parental investment decision concerned with opti mal allocation strategies between parents and young and how these can be affected by resource conditions. When weather conditions were "good" (warmer and sunnier), parents did not have to lower their own selffeeding to increase the arnount of food delivered to larger broods as they did when conditions were "bad" (cold and wet), Only in "good" weather conditions did parents suffer no mass loss as a result of increased parental effort, and incur no increased costs from raising larger broods. In addition, "good" weather conditions rneant that f1edging mass in larger broods was similar to that in smaller broods, which suggests that a reduction in the survival chances of fledglings from larger broods only occurred in "bad" weather conditions. The differenti al allocation responses shown in both years are discussed in terms of parental strategies to cope with increased brood demands.