In message <Pine.ULT.3.91.960512232937.28904A-100000 at elwha.evergreen.edu>
writes:
>
> On Sun, 12 May 1996, Dan Stephens wrote:
>
> > At Atkin's Lake in Douglas Co. (11 May) a Western and Clark's Grebe
> > starting to court.
>
> Do you mean a male of one species and a female of the other were engaged
> in courting? Has this been seen before? Are the mating dances of the
> two species noticably different? Details, we need details. If this is a
> regular event, it obviously has implications for their species status.
>
> Burt Guttman guttmanb at elwha.evergreen.edu
> The Evergreen State College Voice: 360-866-6000, x. 6755
> Olympia, WA 98505 FAX: 360-866-6794

Bert, I couldn't tell if they were of different sexes, just some rudimentary
head bowing between two grebes (a Western and a Clark's) . Yes, interspecies
pairs are known. John Ratti (The Auk 96: 573-586) reported "Only two mixed pairs
were noted in over 600 independent pair observations in California and Oregon."
and from other studies cited in Ratti: "a combined total of 249 dark-phase
pairs, 34 light-phase pairs, and 5 mixed pairs on Bear River Refuge in Utah."
So, if this is a mixed pair it is rare; if they breed on Atkin's also rare to
see Western Grebes nesting on an ephemeral lake.
I believe the reproductive isolating mechanisms are morphological, I have not
noticed any difference in their mating dances. There are references on Western
/Clark's behavior in the Auk index for Vols. 98-107 (just don't have time
to look them up now - still got 10 zo exams to grade). Yes, the devil's in the
details.
Dan

Dan Stephens (509) 662-7443
Dept. of Biology fax: (509) 664-2538
Wenatchee Valley College e-mail: dstephen at ctc.edu
1300 Fifth Street
Wenatchee, WA 98801