Hi MD Birders:
Since we just had a recent report of a Western Grebe in Maryland
(Castaways, Berlin), this just-published study caught my eye ...
At the risk of trying to simply this ... I think it basically says
that in a Utah study of Western and Clark's Grebes, about 6.5% were
found to be visually intermediate between the two species, with
another 7.6% not conforming to the classic species descriptions. The
trends seem to be increasing. Within this study are references to
ongoing genetic studies which seem to support lumping the two, again.
In Maryland/DC, both of the Aechmophorus grebes (Western/Clark's) are
reviewable, as would be any individual of the Aechmophorus grebe
group, even if it was not separable as to species.
Clear as mud, eh? The abstract follows ...
Phil
The Wilson Journal of Ornithology 124(4):713-720, 2012
VISUAL ASSESSMENT OF INTERBREEDING BY AECHMOPHORUS GREBES
ANDRE KONTER, Museum of Natural History, Luxembourg
ABSTRACT.- Population composition of Aechmophorus grebes was
investigated in Utah and the occurrence of possible intermediates
between Western (Aechmophorus occidentalis) and Clark's (A. clarkii)
grebes was assessed. Individuals with clearly intermediate traits
represented an aggregated 6.5% (43 individuals) in the populations
investigated while another 7.6% (46 individuals) did not entirely
conform to the description of Aechmophorus grebes provided by Storer
and Nuechterlein. The number of intermediates has increased in Utah
in comparison to historical data. A similar survey in California and
Oregon in 2009 also found increased percentages of intermediates. The
results a priori contradict growing reinforcement of
incompatibilities between both Aechmophorus grebes. Western and
Clark's grebes in these major areas of sympatry appear to interbreed
as frequently in areas of relative allopatry. No evidence against
assortative mating was found. Hybridization for Aechmophorus grebes
may reflect adaptive mate choice rather than a mistake. Introgressive
hybridization may be important and mask real rates of hybridization.
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Phil Davis Davidsonville, Maryland USA
mailto:<PDavis...>
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