Re: [SBB] WCS-GCS hybrid?

["Alvaro Jaramillo" <[[email protected]]>]

Ken

 What an interesting sighting! These hybrid birds have been popping up here
and there in the Bay Area in the last few years, but they are still
extremely rare. In Rising and Beadle's photo guide to the Sparrows there is
a photo I took of one in Half Moon Bay which fortunately I was able to trap
(through SFBBO). If you can get a photo of the bird you saw, that would be
super. There are very few shots still of this hybrid, which is quite rare. 
	Now the DNA work can be interpreted in a different way, these two
species are good species. There is absolutely no doubt about that. They
breed side by side commonly in Alaska and British Columbia, and hybridize
extremely rarely (that is why your observation is so interesting). Using the
most conservative definition of a species, they are as good as they get. The
fact that the two birds share the same mitochondrial DNA (or at least parts
of it) is unusual, but it does not mean that they are the same species. This
type of DNA gets transferred from mother to daughter, so it does not have
the mixing of father/mother of nuclear DNA, therefore it accumulates
mutations more quickly and that is why it is often used to look at
relationships of closely related (= few differences in DNA) taxa. The
problem is that if there is a large scale hybridization event at some point
in the history of the two species, one of the species could pick up and
"fix" the wrong mitochondrial DNA from the relative. This is what is
hypothesized to have occurred with these sparrows, but this was many, many
thousands of years ago. Currently they are behaving like good species, even
though in the past they may have shown a broad-scale hybridization event,
perhaps due to a specific period in the ice age. Something similar has
happened in Townsend's and Hermit warblers, although that is a different
situation as a hybrid zone exists currently between the two species. 

Cheers

Alvaro

Alvaro Jaramillo
[[email protected]]
Half Moon Bay, California
 
Field Guides - Birding Tours Worldwide
www.fieldguides.com
-----Original Message-----
From: [[email protected]]
[mailto:[[email protected]]] On Behalf Of Kenneth Lajoie
Sent: Saturday, April 07, 2007 7:16 PM
To: [[email protected]]
Subject: [SBB] WCS-GCS hybrid?

An interesting migrant flock of white-crowned and
golden-crowned sparrows visited our yard in Mewnlo
Park yesterday afternoon. Most of the birds were
adult-plumage WC and two were adult-plumage GC: the
resident flock is larger and has a few birds still in
imature plumage. One of the birds in the migratant
flock had neither typical WC nor GC plumage. It's
entire head was very light, yellow in front and white
in back, with two very thin black head stripes. It had
no black eye stripes. We suspect this bird might be a
WC-GC hybrid, or maybe a WC-WT hybrid. This bird is of
interest because recent DNA data suggest these two
species (WC and GC) might be variants of the same
species. Has anyone seen a similar bird? 

Take care,  Ken and Andrea Lajoie

PS: The WC and GC flocks should be heading north any
day now. This break in the weather might be the
trigger that sends them on their way.

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