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.
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
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.
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.