Rapid climatic change is reshaping the timing of ecological events worldwide, yet the cascading effects of these phenological shifts across multiple stages of an animal’s annual cycle remain poorly understood. For migratory birds, in which success and survival depend on the precise seasonality of many discrete life history stages throughout the year, such shifts may generate novel trade-offs between reproduction and survival. In this dissertation, I investigate how lengthening autumns influence breeding completion, post-breeding physiology, and migratory phenology and behavior of a long-distance Neotropical migrant, the Black-throated Blue Warbler (Setophaga caerulescens), using a combination of long-term demographic data and high-resolution automated radio telemetry. In Chapter 1, I show that the green season at Hubbard Brook Experimental Forest has lengthened by more than eleven days since 1989, driven primarily by delayed autumn senescence. Birds responded by extending breeding later into the season, gaining higher reproductive output through increased likelihood of double brooding. However, these gains came with sex-specific costs: late-breeding females, but not males, molted flight feathers more rapidly and with reduced structural quality, suggesting compromised flight performance and potential survival costs. Building on these findings, Chapter 2 integrates breeding data with individual tracking to reveal that later breeding; particularly among females that successfully fledged late broods, delayed autumn migration departure. Males, in contrast, were more responsive to immediate weather conditions, departing earlier and preferentially on clear nights. These results demonstrate that prolonged autumns amplify existing sex differences in post-breeding behavior, with females more constrained by reproductive investment and males more flexible to environmental cues. Finally, Chapter 3 extends this framework into the autumn migratory period, testing whether individuals compensate for late departure by altering migration rate or route. Later-departing males migrated faster, partially offsetting their delayed start, whereas females maintained consistent rates regardless of timing. Both sexes shifted toward more southerly departure bearings later in the season, likely shortening migration distance or taking advantage of preferential conditions along their migratory routes. Together, these results reveal that males possess greater behavioral flexibility to mitigate time constraints, while females face stronger phenological carry-over effects from breeding. My research demonstrates that climate-driven lengthening of the growing season might reshape the timing and trade-offs linking breeding and migration, with important sex-specific consequences. These findings underscore how phenological shifts in one season can cascade through subsequent stages of the annual cycle, altering individual performance and potentially influencing population dynamics under continued environmental change.