Michael,

I was in a class recently when someone asked Dennis Paulson what he thought
was his greatest unanswered 'bird question'...As I recall, he answered
something about underwater foraging of diving ducks. As a close second, he
said: "I wish I knew what crows are thinking." I think the implication
was that crows often do very complex things, perhaps for social interaction
alone.

Rick Romea "We might as well be walking on the sun"
Seattle, WA - Smashmouth

rromea at stioptronics.com
206-523-5831 (Home)
206-827-0460 X 316 (Work)


----------
> From: Michael Price <mprice at mindlink.bc.ca>
> To: tweeters at u.washington.edu
> Subject: Crow Roosting
> Date: Monday, October 20, 1997 3:15 PM
>
> Hi Tweets,
>
> This may be one of the greatest stupid questions ever voiced in
> Tweetersville's town square. Why do crows roost communally?
>
> Late yesterday afternoon and evening, I was watching a crow messing
around
> in a tall, fairly dense cedar. As evening began, more and more crows went
by
> high overhead to their roost site, wherever it may be. Well, crows often
fly
> many kilometers to their roost sites and the flocks can be enormous,
usually
> several hundreds and often over a thousand. The pre-roost staging flock
at
> Still Creek along the Vancouver BC/Burnaby boundary can number well over
ten
> thousand birds before they head over to the roost on Burnaby Mountain.
>
> I was idly thinking about this while watching the crow in the cedar,
> thinking that if that crow wanted to save itself a long flight and still
> stay safe from horned owls, it could simply stay where it was and burrow
> deeper into the cedar, and then the question came up: why do they bother
at
> all with these long pre-roosting flights? Why don't they simply dive into
a
> nearby dense tree, of which there is certainly no shortage in either
local
> shoreline-abutting forest or city plantings?
>
> So why do they undertake often long flights twice a day--often heading
out
> from the roost site in heavy pre-dawn dusk and returning to it in equally

> deep evening twilight--sometimes going extensive distances across water,
> such as crossing Burrard Inlet from Point Grey to a roost site in the
> forests on the side of Mount Hollyburn or Black Mountain in West
Vancouver,
> a distance of about 10 km (6 mi), most of over open water. Why? There's a

> *ton* of good cover in the mature coniferous forest of Point Grey. Why do

> they seem to head up to mountainside roost-sites? There's just as many
> horned owls there as the forest on Point Grey and it's pretty much the
same
> type of forest. Over water, they're vulnerable to falcons and eagles, in
a
> flock they're equally so to falcons and goshawks (there was a gyrfalcon
who
> wintered mostly on a high-rise apartment near the mega-busy intersection
of
> Kingsway and Willingdon near the Still Creek staging area, whacking a
> couple-three crows a day; what a picture: the falcon snoozing on the
traffic
> light or telephone poles right *at* the 10-lanes-total intersection while

> armies of trucks and cars roared by).
>
> Is it useful to note that both the Black Mt./Hollyburn and Burnaby
Mountain
> sites are in similar mature second-growth doug-fir and redcedar forests
and
> both are south-facing? That, though some cross the great water
(age-sorting
> at roosts?) most of the crows on Point Grey fly east in large (500+)
flocks
> at sunset, presumably to Still Creek and on to Burnaby Mountain, a
distance
> of some 20 km (12 mi) from there?
>
> So, what would be the advantages of this system of mass-roost, radiation
> from that site to forage areas? If it didn't confer some advantage, a
smart
> animal like a crow wouldn't do it. I'm missing something obvious here.
Help!
> Any ideas?
>
> Michael Price We aren't flying...we're falling with
style!
> Vancouver BC Canada -Buzz Lightyear, Toy Story
> mprice at mindlink.net
>