Abstract
Montane birds experience a range of challenges that may limit their
breeding success, including nest predation and severe climactic
conditions. The continuing effects of climate change are causing shifts
in biotic and abiotic factors that may compound these threats to montane
bird species. In northeastern montane forests, many bird species are
shifting downslope, potentially as the result of increased precipitation
and temperature at higher elevations. Although lower elevations might be
more favorable in terms of climactic conditions, nest predation is
higher at lower elevations. Thus, montane birds might be faced with the
opposing pressures of adverse climactic conditions at higher elevations
and increased predation at lower elevations. We monitored nests of
Swainson’s thrush (Catharus ustulatus) along an elevation gradient in
the White Mountain National Forest in New Hampshire in 2016, 2018, 2019
and 2021 to examine the effect of biotic and abiotic factors on nest
survival. We found a significant negative effect of rain intensity
(millimeters per hour per day) on daily nest survival, suggesting that
heavier rain per hour decreases Swainson’s thrush daily daily nest
survival. Moreover, we found a negative interaction effect of elevation
in conjunction with minimum daily temperature and average daily
temperature, suggesting that at higher elevations, temperature,
specifically on colder days, decreases Swainson’s thrush nest survival.
Our results provide evidence for a potential mechanism of how climate
change will affect nesting survival of montane breeding birds as heavier
precipitation events become more frequent and intense, a likely outcome
due to the changing climate within the White Mountains and other montane
ecosystems, putting other passerine species at risk in this system.