My research focuses on the evolutionary ecology of ecological specialization. Many studies cite specialization as a characteristic associated with population declines and an increased risk of extinction across a wide variety of taxa, yet local specialization is also a major mechanism behind the creation of new diversity. The first part of my dissertation will focus on measuring niche breadth of six species of sparrows that colonized northeastern tidal marsh habitats at different time scales, and thus show different degrees of specialization for tidal marsh habitats. My goals are: 1) to determine if niche breadth varies among traits, and 2) to test predictions of the Niche Variation Hypothesis, and determine how habitat gradients and competition affect patterns of intraspecific variation in niche breadth across spatial scales. I will also use phylogenetic approaches to explore the effect of specialization on patterns and rates of diversification among a larger suite of species. I hope this information will elucidate which factors might facilitate or constrain changes in a species’ niche over evolutionary time and increase our understanding of species’ ability to adapt to environmental change.