Evolutionary biologists are concerned with understanding the diversity of mating systems found in the animal kingdom and the factors that affect those systems. One important factor that influences the mating system is the amount of parental care that males give. This in turn is influenced by a male's confidence of paternity; that is, a male should not willingly care for offspring if there is a reasonable probability that they were fathered by a different male. Thus, paternity confidence is an important question in species that are monogamous and have high levels of male parental care. Although this question has interested scientists for some time, technological advances (DNA fingerprinting) have only recently made exploration of the question feasible. This research explored this question for the zebra finch, a bird native to Australia that has long-term, often life-long, pair bonds and substantial male care. The species is ideal for study because it is possible to combine experimental (non-invasive) laboratory studies (in Illinois) with investigation of free-living birds (in Australia). This project will increase our understanding of animal social organization. Findings of this study will be integrated with those of other species, resulting in generalizations that should increase our understanding of the process of social evolution in humans -- which also have high male parental care -- as well as other species.