Urban environments pose novel challenges for songbirds, and the degree of urbanization can influence nesting success. We used a multi-year (2013–2021) quasi-experimental design to understand the relationship between urbanization and various nesting parameters derived from 380 Black-crested Titmouse (Baeolophus atricristatus; hereinafter BCTI) nests in nest boxes installed across an urbanization gradient (i.e., rural, and low, moderate, and high levels of urbanization) in San Marcos, Texas, USA. The number of eggs, nestlings, and fledglings per nest were negatively influenced by clutch initiation date but not by level of urbanization or year. First clutch initiation date was correlated with level of urbanization, with nests in areas with any level of urbanization being initiated approximately 12 d earlier than rural nests. First clutch initiation dates for all nests were also affected by weather, with warmer mean daily high February temperatures prompting earlier nest initiation. Nest success was similar in rural areas and in areas with low or high urbanization, but was significantly lower in moderately urbanized areas. Nest success was also negatively correlated with clutch initiation date. Overall, our results indicate that BCTI are demonstrating behavioral plasticity to urban environments with earlier lay dates, but that increasing urbanization does not reliably predict changes in nest success. Thus, different degrees of urbanization potentially act as source–sink locations for BCTI populations.

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