Investigation of brood sizes of three, five, and seven of the tree swallow.

Abstract

The following report is from a study conducted to determine if a correlation existed between the rate of growth and the brood size of the Tree Swallow Iridoprocne bicolor. Evolutionary theory states that birds are selected to lay a number of eggs which will produce a number of young that have the best chance for surviving. This optimal number may be under selective pressure from loss to predation, variable weather, limited food supply, and other environmental forces. These pressures also influence the parents which in turn are selected to devote an amount of energy to parental care needed to raise the young. Kuerzi observed that clutch size varied from three to seven eggs, but that no correlation existed between the duration of nesting period and size of brood. One may then ask, if the parents of a brood of seven increase their parental effort will the rate of growth of their young be the same as broods of three or five? Or, do the parents of seven act in more of an r-selected manner and devote the same amount of time to their young as other adults of smaller broods, but rely on the larger number of young to make up for any reduction in quality of the individual offspring? It is the purpose of this study to find if a correlation exists between the growth rate and the size of broods. It was further hoped to determine if birds were fledgling at different rates of development, and if so, if these rates correlated with specific brood sizes.