Biological invasions are pervasive, alter ecosystem sustainability, and can reduce native biological diversity (Vitousek et al. 1996). Ecologists are scrambling to predict where and when new invaders may strike (Lodge 1993; Fagan et al. 2002). Urbanization has created a number of new ecological niches which, after remaining empty for some time, are increasingly being colonized or invaded by vertebrates (Erz 1966). One of the major disputes in evolutionary biology concerns the rate at which species evolve to occupy new niches (Diamond 1986). How quickly are animals adapting to these new habitats and what makes them successful colonists?