-----Original Message-----
From: Martin J. Muller <martinmuller at email.msn.com>
To: Bonnie Stout <bestout at sfu.ca>
Cc: tweeters <tweeters at u.washington.edu>; Deb Beutler
<dbeutler at wsunix.wsu.edu>
Date: Saturday, November 14, 1998 1:24 PM
Subject: Re: Synchronized diving and some grebe flirtations

(snip)
>To follow Deb's interesting description of the Western and Clark's grebe
>encounter: what time of year was that? An interesting article that
discusses
>a possible explanation is Nuechterlein, G. K, and D. Buitron. 1998.
>Interspecific mate choice by late-nesting male western grebes. Behavioral
>ecology 9: 313-321. Basically as the breeding season progresses the male
>Western grebes get less choosy and start responding more to Advertising
>(calling) Clark's Grebes.
(snip)

It was very early in the spring (late April or early May) before any of the
grebes had started nesting (late May in southern Idaho). That's why I
assumed the male was just confused by another grebe showing up and not
actually trying to court it.

>By the way Deb, have you found the diving behavior to be a reliable way of
>sexing grebes? I never heard of this. As in all grebes, close comparison of
>the bills (in addition to larger male body size) will usually help
determine
>sex. The male has a heavier, especially higher bill. In both Western and
>Clark's, the female's lower mandible appears thinner giving her bill a more
>"upturned" quality.

I generally don't use it to sex grebes unless the grebes are clearly paired
and are the only birds around (so I'm not confusing them with other grebes)
and it is late winter or early spring. The idea that females spend more
time underwater than males, at least in the spring, came from a class
project I did for behavioral ecology. I hypothesized that in spring,
females should spend more time underwater foraging than males of the same
species because females would need more nutrients to prepare for egg-laying.
I then went to local reservoirs and lakes and followed the diving behaviors
of pairs of diving ducks. I used diving ducks because they are sexual
dimorphic. I used paired birds so I could compare the male to the female in
the same situation and I found that the females did spend significantly more
time underwater than the male, regardless of habitat (lake or river) or time
of day or species of birds. The females dove nearly constantly while the
male often spent several minutes on the surface, often preening or just
loafing. I haven't actually tested it in grebes; it would require marked
birds because usually you do this from a great distance so you don't disturb
the birds. I assume the same pressure would be on female grebes and they
would forage (dive more) than males in the spring. I haven't tested the
idea during the breeding season or after the breeding season. You might not
find a difference in grebes (which share parental care) compared to ducks
(which generally don't share parental care). It would be a cool study.
(During my class project, I also found bigger species of birds dive longer,
fish-eating birds dive longer than plant/invertebrate eating birds and
habitat affects diving behavior, usually longer in the river than in the
lake.)

As far as the gulls following the Hoodies during the diving, I assumed the
gull was waiting for one of the birds to surface with a fish so it could
steal it.

Deborah K. Beutler
Dept. Zoology
Washington State University
Pullman, Whitman Co., WA

dbeutler at wsunix.wsu.edu