In choosing sites for a conservation reserve network, representation of the greatest number of species in the sites selected is a common objective. This approach implicitly assumes that all species have equal conservation value. An alternative objective is to represent the greatest genetic diversity in selected sites. This approach gives greater weight to species that are more genetically distinct. Such species tend to contain more unique genetic material, which would be lost if such species became extinct. In this paper, we calculate a diversity measure for a given set of species based on the branch length of the phylogenetic tree for the set. We use genetic distances between bird species in 147 genera based on the results of DNA hybridization research. Distribution information for bird species in the US comes from the Breeding Bird Survey. We compare resulting conservation reserve networks when the objective is the number of genera represented versus the diversity of genera represented. We find that the different objectives produce notably similar results. (C) 2000 Elsevier Science Ltd.