Demographic drivers of black-throated blue warbler population dynamics at the trailing edge and core of the species' range

Species ranges are shifting poleward and to higher elevations in response to climate change. Very few studies have determined how demography links environmental change to range shifts. To investigate the demographic drivers of range shifts, I examined spatial and temporal variation in population density and demography of black-throated blue warblers (Setophaga caerulescens) near the core and trailing edge of the species range. Population density declined at the trailing edge, but remained stable in the core of the range, which supported the hypothesis that this species range is shifting. Survival rates were higher, but recruitment rates were lower at the trailing edge, suggesting that low recruitment may explain trailing-edge population declines. Future work should seek to understand how climate influences recruitment at trailing-edge range margins via shifts in reproduction, juvenile survival, or dispersal.