Saturday, July 18, 2015

Snowy Owl Perch Selection in Cold Weather

The winter of 2013-2014 was remarkable in eastern North America for an unprecedented southward movement of Snowy Owls (Bubo scandiacus) with high counts around Ontario and records extending far into the southern USA (ebird 2013). It has been theorized that this movement was related to an excellent breeding season in northern Quebec, due to very high populations of small mammals (Mactavish 2013). This article examines an interesting behavior noted among a large concentration of Snowy Owls during a particularly cold period from January 21-22, 2014.

During January 2014, I spent multiple days conducting field work on Wolfe Island, Frontenac; a known location for high winter raptor concentrations (Weir 2008). The island was driven in a grid pattern, with locations, individuals, age and sex noted as the birds were observed. This served to prevent any sort of duplication when counting. While raptors in general were in very low numbers (pers obs), Snowy Owls were in particular abundance. Some sample high counts were 24 (Jan 15), 33 (Jan 22) and 23 (Jan 30). The high count on January 22 was obtained in a remarkable 3 hours from 2:30pm to 5:30pm; likely aided by a change in the birds’ typical behaviour. Immediately upon arriving at the island, I noted that the first individuals were all perched high in trees or telephone poles. The trend continued, were birds were typically perched at a height >3m for the next 150 minutes. The first individual found on the ground wasn’t until after sundown when a juvenile female was present on a high slope in a snow covered hayfield. She was the 26th individual of the day. Of the final 33 birds tallied, only 2 were on the ground and one additional bird was >2m up on a pile of lumber.

The weather from January 21-22, 2014 could be categorized as “very cold”. The Kingston Airport recorded a minimum temperature of -29C at 6am, with a wind-chill reading of -41C, on January 22 (Environment Canada 2014). During the survey period, temperatures ranged from -18C to -21C with wind-chills in the range of -26C to -28C. Winds were light (beaufort 2-3) and generally from the SW. Cloud cover was limited to a small area (20%) of thin high level cloud.

I theorized that the Snowy Owls had moved to higher perches to avoid sitting on the icy and snow-covered ground that dominated the Wolfe Island landscape. Extremely cold temperatures the previous night had warmed <10C during the daylight hours, leading me to believe that the birds had perhaps perched high to take advantage of the early morning sun and simply stayed there the entire day. The gentle breeze should not greatly affect the birds’ sensitivity to wind-chill. During the first 150 minutes of observation (23 birds observed) I did not note any individuals to be actively hunting, with the majority (>90%) not moving from their perch was I observed them. It wasn’t until dusk that I observed the two individuals on the ground, indicating they had possibly become active before I was able to observe them at their daytime roost location.

This interesting behaviour likely lead to 22 January 2014 being my highest count of Snowy Owls throughout the survey dates. My ability to detect them was greatly increased due to their preference of prominent perch locations, avoiding their typically camouflaged haunts low to the ground. This situation was likely compounded by the fact that there was an ample number of perches >3m for Snowy owls to choose from, after the 2013 Central and Eastern Canada ice storm damaged the tops of many trees throughout southern Ontario, including Wolfe Island (see; Coulson 2013). With that said observations before and after 22 January yielded lower counts of Snowy Owls, all of which had warmer maximum and minimum temperatures recorded.

These observations may give credence to the idea that days with temperatures well below the daily average could prove to be the ideal conditions for observers to detect Snowy Owls and/or conduct accurate counts of individuals present over a specific area.

Figure 1. Snowy Owl, Wolfe Island. 22 January 2014. Perched high on an ice damaged branch. Photo: Brandon R. Holden

Literature cited:

Coulson, G. 2013. Ontario Weather Review – December 2013. Environment Canada. 3pp.

eBird. 2013. Arctic wanderers – Snowy Owl invasion 2013. 11 December 2013. ( Accessed 23 January 2014.

Environment Canada. 2014. Climate Data Online. Retrieved from Accessed 22 January 2013.

Mactavish, B. 2013. “300 Snowy Owls in Newfoundland Weekend – An Explanation.” [Web log entry] The Bruce Mactavish Birding Newfoundland Blog. 11 December 2013. ( Accessed 23 January 2014.

Weir, R. 2008. Birds of the Kingston Region, 2nd edition. Kingston Field Naturalists. 611pp.

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