Canadian Butterflies Expand Range As Climate Warms

Warming temperatures in Canada are causing butterfly species to extend, rather than contract, their geographical range, according to a study published in Environmental Entomology by University of Winnipeg Associate Professor of Biology Richard Westwood and his colleague David Blair.

Northern Ranges Extended
The University of Winnipeg scientists measured the responses of 19 common butterfly species of the boreal forests of Manitoba, Canada to temperature changes experienced there over the period 1971-2004, focusing on each species' date of first appearance, week of peak abundance, and length of flight period.

The two Canadian researchers report “the early autumn and winter months warmed significantly” while spring and summer temperatures were little changed over the course of the research period. Consequently, "adult butterfly response was variable for spring and summer months."

However, "13 of 19 species showed a significant increase in flight period extending longer into the autumn" when "flight period extensions increased by 31.5 ± 13.9 days over the study period." In this regard, they note "two species, Junonia coenia and Euphydryas phaeton, increased their northerly ranges by ~ 150 and 70 km, respectively."

"Warmer autumns and winters may be providing opportunities for range extensions of more southerly butterfly species held at bay by past climatic conditions," Westwood and Blair explain.

In other words, the southern range of Canadian butterflies is essentially unchanged, and their northern range is expanding.

Other Studies Confirm Results
The scientists note other investigators have obtained similar positive results, stating "northward expansions in butterfly species range correlating with northward shifts in isotherms have been documented in both Europe and North America, while "in Canada, the Gorgone checkerspot (Chlosyne gorgone, Hubner) and the Delaware skipper (Anatryone logan, W.H. Edwards) have recently expanded their northern ranges significantly (Kerr, 2001)."

Warming temperatures indeed appear to be beneficial to the Canadian butterflies.

Craig D. Idso, Ph.D. (cidso@co2science.org), is lead author of Climate Change Reconsidered, published by the Nongovernmental International Panel on Climate Change (NIPCC). An earlier version of this article appeared on the NIPCC Web site. Subscriptions to the NIPCC email distribution list are free of charge, and can be ordered at http://www.nipccreport.org/about/emailsignupform.html.