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animal species

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Snowy Owl

The Snowy Owl is one of the predators that can periodically be found on Bylot Island. This large northern owl breeds in the open tundra of the circumpolar Arctic and winters in more southerly areas such as southern Canada, Northern United States and Central Eurasia, where it inhabits prairies, marshes and open fields.

female Snowy Owl with young - femelle Harfang des neiges avec un jeune © Austin Reed

young Snowy Owl - jeunes Harfangs des neiges © Joël Bêty

Although known as a migrant, the Snowy Owl’s migratory movements are unpredictable, believed to be related to fluctuations in the abundance of its main prey, the lemming. In fact, lemming populations are cyclic, going through peaks of really high to really low abundance every 3 to 5 years (see Lemmings). Even though the Snowy Owl is able to prey upon other mammals, such as Arctic Hares (Lepus arcticus), fluctuations in lemming populations have large consequences on their breeding biology. When lemmings are abundant, Snowy Owls may lay large clutches of 7 to 12 eggs, but they can also reduce their clutch size to 3 to 5 eggs when lemming abundance is moderate.

During very low lemming population sizes, owls may not nest at all or they may leave the area to breed in regions where the amount of preys is higher. In order to fill this knowledge gap, a new study was initiated in 2007. We captured, banded and equipped owl female adults with radio transmitters to track their migratory movements for up to 2 years following a lemming peak on Bylot Island. We want to visit their other breeding grounds to determine the factors that influence the selection of these particular sites.

On Bylot Island, nesting Snowy Owls have usually been seen during summers of high lemming abundance. During those summers, 10 to 22 nests have been found and monitored in the Qarlikturvik Valley and at the goose colony. Laying dates (date when the first egg is laid), hatching dates (date when the first egg hatches) and number of eggs in each nest (clutch size) were monitored. All nestlings (young Owls) where also marked with a leg-band. This marking technique could help us determine whether Snowy Owls eventually come back to their natal ground or not.


Snowy Owls Cyclic Presence

As mentioned above, Snowy Owl nests have been found mostly in years of high lemming abundance, which in this case corresponds to 1993, 1996, 2000, 2004, 2008 and 2010.

Clutch Size

The number of eggs observed in Snowy Owl nests on Bylot Island averages 7.1. This number varies among years but the variation is not related to the intensity of the lemming peak.


Egg Laying and Hatching Dates

Over the years, egg-laying and egg-hatching dates varied, probably reflecting variations in the environmental conditions themselves. On average, the first egg is laid 22 May and hatching occurs around 23 June.