Tweeters,

On a similar vein to what Dennis posted, it seems to me that habitat or
geographic separation of golden-crowned and white-throated (I got it right
this time) sparrow populations may contribute to the likelihood of
hybridization. To produce a hybrid offspring, the parents must be closely
related, probably sharing a common ancestor sometime in the recent
(hundreds of thousands of years?) past.

>From what I have gathered, these are not usually sympatric species. Some
isolating factor produced two separate species with differing appearances,
behavior, and habitat affinities. It is the isolation from one another that
allowed for the evolution of separate species. When the isolating factors
break down (perhaps a glacier melts or one of the two species simply begins
to expand its range in response to habitat changes or a particularly good
year for producing babies), all of a sudden these two closely related species
come into contact. Since the isolating factors have been geographic or habitat
based rather than behavioral (behavioral isolating mechanisms sometimes
maintain the integrity of closely related species living in the same habitat),
once the two species have a chance contact, there is a likelihood of
hybridization.

But you won't know for sure unless you grind 'em up.

Kelly McAllister (too much caffeine)