Hello,

Scott Richardson wrote:
>I have heard a suggestion that synchronized diving is a predator-defense
>mechanism, in that nobody is left alone on the surface and everyone
resurfaces
>(relatively) synchronously. The recent study I have in mind was on scoters, I
>believe, although it might have been goldeneyes. It was done by videotaping
>foraging flocks and hitting the rewind button a lot (I suspect).
>

Yep, you are correct. The papers you may be thinking of if anyone is
interested are:

Beauchamp, G. 1992. Diving behavior in Surf Scoters and Barrow's
Goldeneyes. Auk 109:819-827.

Schenkeveld, L. E., and R. C. Ydenberg. 1985. Synchronous diving by surf
scoter flocks. Canadian Journal of Zoology 63:2516-2519.

These ducks are munching on sedentary food (mussels and such). With mobile
prey the same reasons could apply. Another possibility is that it makes
for more efficient capture of prey.

This (Semiahmoo Bay) is the only place I have see synchronous diving in
grebes, though there are a few reports of it in HOGR and EAGR elsewhere
(ie. King, B. 1971. Group feeding by Slavonian Grebes. British Birds
64:372. AND Robertson, H. G. 1997. Group foraging and diurnal activity
of Black-necked Grebes at sea. Ostrich 52:248-250).

The courtship/display possibility is one I never thought of - you never
know! It would sure be nice to film them underwater as Michael P.
suggests! In the case of the Scoters they are definitely munching on
mussels. I can only presume the grebes are also are foraging, but one
never knows with these grebes! I've watched them persist in this behavior
for hours. They typically swallow prey underwater. And I have to guess at
what they might be chasing.

Bonnie Stout
Burnaby, BC
bestout at sfu.ca


Bonnie Stout
Department of Biological Sciences
Simon Fraser University
Burnaby, BC V5A 1S6 Canada
ph:(604)-294-9355
bestout at sfu.ca