Breaking News: Scientists reveal true cause of Snowy Owl irruptions

Dr. Jean-Francois Therrien with Snowy Owl
After centuries of believing the reason for the irruption, scientists now reveal the true catalyst of Snowy Owl migration.

A team of Canadian biologists including Hawk Mountain Sanctuary’s Dr. Jean-Francois Therrien  announced their recent finding that Snowy Owls  dispersing  south into the United States in some years but not others do so in response to an abundance of food (lemmings) in the Arctic, not a shortage as previously believed. The full report  was published recently in the scientific journal Oecologia.

Dr. Therrien states that long-term studies on Bylot Island in Nunavut, Canada confirmed that the numbers of snowy owls fluctuates tremendously among  years in concert with those of lemmings, the owls’ principal prey. However, the emerging story is that rather than having a winter irruption composed of starving adults following a low lemming year, we are witnessing the opposite relationship: an abundance of lemmings, and exceptionally successful owl breeding activities, the summer before in the Canadian Arctic produces large irruptions into the US during the following winter.

“Simply put, a Snowy Owl baby-boom down south usually follows a lemming feast in the Artic,” explains Dr. Therrien, Senior Research Biologist at the Sanctuary.

Dr. Therrien has worked in tandem with Hawk Mountain Sanctuary to conduct this research. Hawk Mountain Interim President Dr. Keith Bildstein shared his excitement for this important news.  “This is significant information as allows finally to understand what is driving the irruptive movements of this  Arctic icon.”

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About Hawk Mountain:

The 2,500-acre Hawk Mountain Sanctuary is the world’s first refuge for birds of prey and is open to the public year-round by trail-fee or membership, which in turn supports the non-profit organization’s raptor conservation mission and local-to-global research, training, and education programs. To learn more about Hawk Mountain or other programs, please call 610-756-6961 or visit

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