crows as tubenoses
nettasmith at attbi.com
Sun Jan 20 09:50:46 PST 2002
This morning (1/20/02) the usual flight of crows went over the house, mostly
before 08:00 but with lots of stragglers. Today I watched them for a good
part of the flight, which lasted at least 15-20 minutes. During that period
hundreds of crows passed overhead, perhaps as many as a thousand - and this
is just one of their flight paths, and already 5 miles or so from the Foster
Anyway, what made this more interesting than usual was the way they were
flying. A very brisk wind came out of the SW, and the crows, heading NNW,
were flying down this wind very fast, losing altitude. They would then make
a 90° left turn (thus heading WSW), and their speed would decrease suddenly
as they flapped vigorously into the strong wind, rapidly gaining altitude as
their lift increased tremendously. After gaining some altitude, they would
turn into their original direction and zoom downwind again.
Groups of crows - up to perhaps 20 birds - would make this turn almost
simultaneously, and I saw several near collisions as a group of downwind
birds converged on a group of upwind birds.
This flight style is essentially the same (except for a lot more wing
flapping) as that used by tubenoses (finally to the subject) at sea. It is
called dynamic soaring, and albastrosses and shearwaters can fly
indefinitely over the ocean by using this method - downwind picking up speed
but losing altitude, then sharp turn upwind to gain altitude, the downwind
speed providing momentum for this maneuver. Then as they gain altitude and
lose speed, perhaps just before stalling, they turn and glide downwind
again. The birds don't actually head exactly upwind or downwind, as they
are better off at an angle to those directions, just as a tacking sailboat.
They can go in a preferred direction very efficiently by using this method.
If you watch gulls on a windy day at the ocean, you'll see they are doing
the same thing.
But I have never seen a songbird do this before.
Netta Smith and Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
More information about the Tweeters