| Abstract: | Much previous research has focussed on the role of food supply in determining the growth and the survival of avian offspring. More recently, acid deposition in some ecosystems has demonstrated that in addition to energy, birds also need to acquire sufficient nutrients such as calcium to be successful. Whether procurement of adequate levels of calcium can limit reproductive success in areas that have not been impacted by acid rain remains equivocal. We tested whether calcium affected reproductive success of tree swallows Tachycineta bicolor by feeding extra calcium to nestlings during the brood-rearing period. Our manipulation did not enhance the survival of offspring, however, provisioning of extra calcium resulted in nestlings showing enhanced rates of growth of mass (all nests) and of ninth primary flight feathers (nests with after-second year female parents), compared to control nestlings. Calcium supplementation also resulted in nestlings having longer feathers and tarsi at age 16 days, and there was evidence that some nestlings receiving extra calcium were heavier at 16 days old. As offspring that have faster growth, or that are in good condition at fledging, often survive better after leaving the nest, these results suggest that calcium availability can limit fitness. Our results are noteworthy because our experiment was conducted in an area with abundant soil calcium where acid deposition has not occurred. The role of calcium in limiting the reproductive performance of avian species may therefore be more pervasive than previously thought. |
