Comparison of Spring Return Dates of Mountain Bluebirds, Sialia currucoides, and Tree Swallows, Tachycineta bicolor with Monthly Air Temperatures

Abstract

The dates of "first observed arrivals" of Mountain Bluebirds, Sialia currucoides, and Tree Swallows, Tachycineta bicolor, have been recorded for approximately 40 years near Lacombe, Alberta, Canada. Examinations of trends of these returns with average monthly temperatures for March and April, respectively, suggest trends for earlier returns and warmer temperatures, consistent with theories of climate warming.