On Mon, 18 Nov 1996, Herb Curl wrote:
>
> I apologize for not looking at much of the literature first. Snowy Owls
> obviously have to hunt in broad daylight above the Arctic Circle in summer.
> When we see them down here in Fall & Winter they're invariably "at rest"
> during the day. The implication, mentioned by someone else, was that they
> hunted at night. Here's the puzzle: there have been several references,
> recently and in the literature, to Snowy Owls feeding on Buffleheads,
> specifically, and other ducks, in general. It would seem extraordinary
> that a Snowy Owl could catch a duck.

During this whole Snowy Owl invasion, I have been kicking myself for not
taking better notes when I heard a talk several years ago by a man who
studies Snowy Owls at Logan Airport in Boston, MA. His talk was so chock
full of information that I have never seen elsewhere (e.g., you can
distinguish four age/sex classes reliably by plumage), and it kills me
how little I remember.

But I do recall a little that relates to Herb's question. Snowy Owls will
take waterfowl, and the population of Snowies at Logan Airport (up to
several dozen have been banded there in some winters) take ducks
regularly. Snowies are longer winged than most owls, and their wings are
definitely more pointed than the woodland owls. Probably as a result of
their build, they seem to be more powerful and manoeverable fliers than
any other owl. I'm pretty sure they take ducks on the wing at least
occasionally. I would imagine, however, that most of the waterfowl they
take by stealth, surprising ducks into flight at short range or picking
them off the water. Ducks may be quite vulnerable to this kind of attack
at night.

I have seen a Snowy carrying around the well picked carcass of a full
grown Canada Goose. While at the time I figured the owl had to have
scavenged a dead goose, the researcher at Logan made it clear that Snowies
did occasionally kill live healthy prey in that size range. His
eyewitness account of a Snowy attacking a Great Blue Heron still sticks in
my mind.

I looked through the owl books in my library - diet studies have found
that in most cases, _breeding_ snowies eat mostly rodents (though only in
one study were lemmings the dominant prey). Where rodents aren't
available during the breeding season, the owls ate rabbits and shorebirds,
ducks, and more.

Wintering Snowy Owls at a much wider variety of prey. The overall picture
is of opportunistic hunting of anything from the size of a small rodent to
a large duck, and occasionally larger. I hand picked some examples where
a study showed Snowies living on larger avian prey. Here are some of the
highlights:

Frank Dufresne (1922, quoted in Bent's Life Histories of Birds of Prey,
pt. II):
As soon as the young ptarmigan hatched, my observations of the
snowy owl became a record of slaughter. I had no way of telling exactly
how many were eaten on account of the softness of the bones, but I do know
that rodent regurgitations practically ceased at this time. Ptarmigan,
both old and young, became the mainstay of the seven pairs of owls and
their combined families...I, myself, have seen one bird kill three full
grown ptarmigan within an hour.

Olaus Murie (1929, also quoted in Bent):
The food of the snowy owl varied with the character of the nesting
ground. Those on the marsh and in the immediate vicinity of great numbers
of nesting waterbirds fed extensively on birds, both old an young.
Others, nesting on drier ground farther from the concentration of
waterfowl, maintained throughout the season a diet consisting almost
exclusively of mice. In marshy areas remains of young emperor geese and
cackling geese and adult old-squaws, eiders, and other ducks, were found.

>From Paul Johnsgard's Owls of North America, a summary of a study by
Campbell and MacCall in 1978. This one seems particularly applicable to
some of our locally invading birds:
In an analysis of prey remains obtained from five snowy owl winter
territories in British Columbia, it was found that grebes and ducks
comprised an estimated 90 percent of the prey intake when analyzed by prey
weight, which usually consisted of birds in the 400-800 gram range of
adult bodily size.

An old study in Atlantic Canada, when they studied these things by
examining stomach contents of shot birds (1902, Napoleon Comeau, quoted
in Bent):
I have examined the stomachs of over a hundred and have found
invariably the remains of the the two species above mentioned [Dovekie and
Common Murre]. The owls in some cases were nothing but a lump of fat.

Another quote from the same author makes me want to visit the outer coast
on a moonlit night:
This bird flies and hunts by day as well as by night, but the
greatest flights are at night. They follow the coast line, as a rule. In
January of this year I saw over a hundred birds in one evening from seven
o'clock to 10:30 P. M.

Yow!

Herb Curl, again:
> Are they perhaps opportunistic
> carrion feeders?

I know carrion feeding is well documented in many owls, as, for instance
when owls feed on animals killed in traps, or are caught in traps
themselves when the traps are baited with meat. I would think that
Snowies would be even more likely than other owls to feed on carrion,
given the scarcity of food in the Arctic in winter and the bonanza that
one dead walrus, for example, would be to an owl. I'm just guessing,
though.

Chris Hill
Everett, WA
cehill at u.washington.edu