Biology Reference
In-Depth Information
Snowy owl
For one thing, there's no evidence that lemming cycles are synchronized throughout the Arctic, and
they may be quite regional. Since snowy owls by nature are great travelers, it's no special feat for them
to move from an area of lemming scarcity to one of abundance. For another, large numbers of snowy
owls migrate annually to the Great Plains area of Canada and the United States without apparent ref-
erence to lemming cycles. Much remains to be learned about the dynamics of the lemming/snowy owl
relationship.
Snowy owls are silent for most of the year. During the breeding season, however, they utter a variety
of sounds, especially a croaking call and a sort of shrill whistle. They may hiss when they or their nests
are threatened, and reputedly also hoot during the breeding season.
Prior to breeding, snowy owls perform a fascinating courtship ritual. First comes the flight display,
in which the male alternately descends with wings arched above his back, then flaps upward, only to
repeat the procedure. Then he begins to bring lemmings, which he deposits in a pile in front of the fe-
male; this performance may signal that he's a good provider, that prey is sufficiently abundant to enable
the parents to raise a brood successfully, or both. Finally the male goes through a variety of strange
poses and then fawns in front of the female to complete his amorous display.
Like the rest of their tribe, snowy owls aren't nest builders. On a hummock or other high point, the
female simply scrapes out an unlined hollow and begins to lay eggs. It's noteworthy that such a location
provides not the slightest protection from the bitter Arctic winds, but allows the nesting pair to watch
for predators in every direction. Protection from the wind evidently isn't important to snowy owls, for
their magnificent plumage has the same insulating power as that of Antarctic penguins and enables
them to withstand the horrific cold of an Arctic winter.
At this point the species' nesting behavior becomes highly unusual. Snowy owl clutches range from
the merely very large—for owls—of five to eight eggs to the huge, with as many as sixteen. The excep-
tionally large clutches are thought to occur only in years when lemmings are extremely abundant, but
that's by no means certain. What is certain is that the female lays one egg roughly every two days, yet
she must begin incubation as soon as the first egg is laid, lest it freeze solid in the frigid Arctic weather.
If she lays a dozen eggs, this means that nearly a month elapses between laying the first and last eggs
in the clutch. Each egg takes about thirty-two days to hatch, so the last egg has barely been laid by the
time the first one hatches!
With the nest on the ground, the fuzzy gray owlets don't have to fledge in order to leave it. They
merely step out of the nest, long before they can fly, and nestlings from the early eggs walk away soon
after siblings from the later eggs have hatched. The owlets move about, but remain near the nest, where
the male brings them food. The female is tied to the nest until the last owlet leaves, which can be two
months in the case of a very large clutch.
Snowy owlets fly about seven weeks after hatching, so raising an exceptionally large brood, from the
time the first egg is laid until the last owlet takes wing, can consume more than three and a half months.
Since that represents virtually the entire Arctic summer, the process of raising such a large brood places
