The age of females did affect nesting success in some ways. Older females fledged more chicks in one year of the study, and in both years fledged heavier chicks on Pine Point. Young females laid fewer eggs in one year of the study, and nested later. In 1988, few young females nested at all, which may reflect an optimization of lifetime reproductive success. Although there were differences in temperature, wind, and insect abundance between the two nesting sites of Tree Swallows at UMBS, these differences did not appear to affect significantly the nesting success of the swallows. The nesters which appeared most successful were at the Ballfield one year, but at Pine Point the next, suggesting that site quality depends heavily on yearly environmental conditions. To better describe the ways in which habitat variation affects nesting success, two sites would be neeeded which differ more or are farther apart than are the sites at UMBS. The number of chicks fledging did not vary greatly among the four groups; however, significant differences in nestling growth and weights previous to fledging indicated that there may have been differences in parental abilities. Since weight prior to fledging is a predictor of fledgling survival, those females raising the heaviest chicks should have more chicks survive and thus potentially higher lifetime reproductive success. Other factors which could affect nesting success, but which could not be adequately assessed in this study, were the foraging range of the swallows, quality of nearby feeding areas, and the ages of the males. The effects of age of parents and habitat variation on nesting success would be more suitably examined over a longer period of time, both to minimize the impact of year-to-year variation and to establish a population of known-age birds (both males and females). A long-term study would also provide some information about the survival rates of fledgelings, and thus the lifetime reproductive success of their parents.