Hi Tweets,

At Canada Place in downtown Vancouver BC this afternoon, I watched an adult
Glaucous-winged Gull Larus glaucescens in sustained pursuit of a
Northwestern Crow Corvus caurinus well out from land over the waters of the
Inner Harbor. As the crow was not visibly carrying anything in its bill, I
speculate that the attack--the first I've ever witnessed involving these two
species--was either predatory or, more likely, kleptoparasitic.

At this time of year, one very frequently sees single crows flying low over
the water, sometimes quite far out in the harbor, and more than one distant
cormorant has resolved in the bins to be a crow. They seem to be constantly
shuttling back-and-forth from their nests in Stanley Park to forage areas in
East Vancouver. They're the only resident land-bird which seem unperturbed
at crossing daily stretches of water even several kilometers wide, an
insouciance which puzzles, as there's Bald Eagles Haliaeetus leucocephalus
here all year (a couple of nesting pairs nearby, actually, and a ton of them
in the winter), passage and winter-resident Peregrine Falcons Falco
peregrinus and passage Gyrfalcon F. rusticola. No end of potential raptorial
threat, there.

The crow was heading back toward Stanley Park and about half a kilometer
out, with another kilometer to go to make nearest landfall in its flight
direction when an adult Glaucous-winged Gull which had been circling in the
area suddenly dove on it with obvious aggressive intent. The crow eluded the
first dive and for the next thirty to forty seconds had to make violent
evasive moves to avoid being nailed by the gull in sometimes very close
pursuit. After nearly a minute, the gull broke off the attack and glided off
to settle on the water, while the crow put it into top gear and headed for
the park.

On several occasions, I've witnessed successful in-flight attacks on, and
kills of, Rock Doves Columba livia over water by Glaucous-winged Gulls but I
have never before seen this type of sustained attack by a gull on a crow
before. The gull's behavior was identical to that of individual gulls
killing pigeons.

Two possibilities: first, it was attempting to kill the crow--perhaps it
calculated the crow was more vulnerable as a target of opportunity well away
from land; second, and I think more likely, the gull had learned from
observation of the hundreds of crows flying back and forth each day that
crows flying over water *towards* Stanley Park at this time of the year were
likely to be parents carrying a full crop of food back to the nestling
kiddies--like a jaeger harassing a tern, it was hoping for a nice big meal
of propitiatory upchuck.

Michael Price
Vancouver BC Canada
mprice at mindlink.net