You need to read:

Douglas A. Bell Hybridization and Reproductive Performance in Gulls
of the Larus Glaucescens-Occidentalis Complex Vol. 99, No. 3,
May-June, 1997

The Glaucous-winged Gull (Larus glaucescens) and the Western
Gull (L. occidentalisoccidentalis) hybridize along the Pacific Coast
from Cape Flattery, Washington,south through central Oregon. A
hybrid index, based on plumage and soft part colors, wasused to study
the distribution of morphotypes (e.g., pure and hybrid birds), mating
patternsand reproductive performance at eight sympatric and two allopatric
colonies. Mate choiceappears to be weakly positive-assortative. In 1989
in the hybrid zone, L. o. occidentalisexperienced significantly greater
reproductive performance, measured as clutch size and eggvolume
difference, than either L. glaucescens or mixed pairs containing at
least one hybridindividual. Although the hybrid zone has expanded
somewhat
in recent times, the midpoint of the zone and the relative proportion of
morphotypes has remained stable. The hybridzone is situated on a
marine-ecotone. Within the hybrid zone, relative reproductive performance
of L. o. occidentalis and hybrids may shift between years, whereas
L. glaucescensmay experience poor reproductive performance in all years.
The selection-hybridization balance hypothesis may best explain the
L. glaucescens-occidentalis hybrid zone.Key words: gulls, hybridization,
Larus glaucescens, Larus occidentalis, reproductive fitness, selection-
hybridization balance.

And

Douglas A. Bell Genetic Differentiation, Geographic Variation and
Hybridization in Gulls of the Larus Glaucescens-Occidebtalis
Complex Vol. 98, No. 3, May-June, 1996

Survey of morphometric, colorimetric, and allozymic variation in
the Glaucous-winged Gull (Larus glaucescens), the Western Gull
(L.occidentalis) and their hybridsis based on 706 specimens taken
from 33 colony areas located throughout the breedingrange of
both species. Whereas most morphometric characters overlap
between taxa, colorimetric characters exhibited significant
intraspecific and interspecific clinal variation. Canonicai
discriminant function analysis of colorimetric characters clearly
separated pure and hybrid morphotypes and confirmed the intermediacy
of character expression in hybrids.Plumage melanism of the
mantle and primary tips are among the best discriminators of
hybrids. Twenty-five of 32 presumptive genetic loci were polymorphic.
Although there were no fixed differences between taxa, gene frequencies
exhibited significant heterogeneity acrossgeography. Despite moderately
high gene flow (Nm = 2.8 individuals per generation), populations of
the L. glaucescens-occidentalis complex are not panmictic, and the
hybrid zone forms a partial barrier to gene flow. Hybrids are
genetically
more similar to L. glaucescens than to L. occidentalis. The hybrid zone
extends from Juan de Fuca Strait, Washington,south to Coos Bay, Oregon.
A broad zone of introgression extends from the Queen Charlotte Islands
in British Columbia south to Coos Bay, Oregon. The hybrid zone appears
to have expanded in recent years, yet its midpoint near Grays Harbor,
Washington, has remainedstable. Hybridization appears to be responsible
for skewed introgression and elevated genetic diversity in L.
glaucescens.
The fact that L. glaucescens shows high levels of introgression while
maintaining its genetic identity lends support to the hypothesis that
hybridization inbirds may serve as a mechanism for increasing or
restoring genetic diversity in forms thatare adapted to local environments.
Key words: allozymes; genetic differentiation; gene flow; geographic
variation; gulls;hybridization; Larus; morphometrics.

Available in pdf at: http://elibrary.unm.edu/Condor/

> Glaucous-winged x western
> Tweeters,
>
> I've not been able to access the index in the CONDOR journal.
>
> Does anyone out there know what the reproductive capabilities of the
> gull hybrids are?
> We probably have particular interest in the Glaucous-winged x Western
> Gulls in Washington state.
>
> Larry Schwitters
> Issaquah

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Half-a-bee, philosophically must ipso-facto half not-be.
But half the bee, has got to bee Vis-a-vis its entity...
d'you see?
But can a bee be said to be or not to be an entire bee
When half the bee is not a bee due to some ancient injury?
-Monty Python

http://www.pacifier.com/~mpatters/bird/bird.html