Montane breeding birds experience a range of challenges that may limit their breeding biology, such as colder temperatures and increased precipitation at higher elevations. The continuing effects of climate change are causing shifts in biotic and abiotic factors that may compound these threats to montane bird species, who may be faced with the opposing pressures of adverse climatic conditions at higher elevations and increased predation at lower elevations. This dissertation focused on a representative montane breeding bird, the Swainson’s Thrush (Catharus ustulatus) within the White Mountains, New Hampshire, USA and examined how these shifting factors along an elevational gradient influenced their breeding biology. In my first chapter, I evaluated temperature and rain with daily nest survival rate of thrush nests and found that heavier rain events (cumulative rain accrued per day in millimeters) and warmer temperatures at higher elevations, respectively, negatively affected nest survival of this species. In chapter 2, I used stable isotope analysis and estimated the proportion of dietary prey items within the diet of adult birds. This revealed thrushes at lower elevations consumed more high protein invertebrates, such as beetles and spiders, and higher elevation birds consumed primarily lower protein millipedes. In chapter 3, I deployed several automated recording units along an elevational gradient and recorded singing male birds to determine when birds established territory. I found adult thrushes established territory 6 days earlier at higher elevations, and birds established territory 6 days earlier in 2020 than in 2019. Finally, in chapter 4, I evaluated the insulation value of thrush nests and found nests at higher elevations were more insulated. However, when considering the presence of mature nestlings (> 6 days old), this negatively affected insulation value of nests, suggesting that older nestlings may compress and affect the insulative integrity of nests. Additionally, nests that were built with more twigs were poorly insulated and likely more porous, potentially aiding in better airflow and allowing nests to dry efficiently in wetter conditions. This research provides further understanding of the breeding biology of montane birds within a warming climate and suggests that increasing temperatures and more frequent rain events will have severe negative consequences on several important stages of their breeding season.