eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Earlier Spring Arrival of the Mountain Bluebird in Central Alberta, Canada
Myrna Pearman, Leo de Groot, Geoffrey L. Holroyd,
and Stephanie Thunberg
ABSTRACT: Much attention has been given to the topic of bird phenology in response to climate change. While strong evidence supports a general pattern of advancement in spring migrants’ arrival dates with warming temperatures, the mechanisms underlying these changes are not clearly understood. We summarize the spring arrival of the Mountain Bluebird (Sialia currucoides) in central Alberta from 58 years of data and examine the influence of temperature and snow cover on the patterns of arrival. We hypothesized that a significant advance in the Mountain Bluebird’s first arrival date was related to weather variables. In central Alberta, March temperatures increased, and first arrival dates for the Mountain Bluebird advanced 0.33 days per year from 1961 to 2018 or 19 days over the 58 years. However, temperatures on the date of arrival have cooled slightly (2.8 °C) over the study period, and snow depth on the date of arrival decreased slightly (1.5 cm) over the study period, which may influence early migrants’ opportunities for foraging. Although Mountain Bluebirds have arrived at our central Alberta study area considerably earlier over the past decades, temperatures and snow depth have been highly variable, suggesting that the species is likely responding to multiple cues that influence its arrival dates. Given the Mountain Bluebird’s migratory nature, environmental and behavioral stimuli en route to breeding areas likely exert considerable influence on arrival dates.