Tuesday, January 26, 2016

Post #52 - Play that funky music, white bird!

So....this bird has been hanging around Orange County for the past few weeks. I first observed it at Mile Square Park two weeks ago, and I more recently ran into it again at Carl Thornton Park. It was fairly approachable the second time, letting me get close enough to snap this photo with just a 50mm lens!

Mystery goose!

What on earth is this bird? It lacks the black wing primaries of a Snow Goose, as it does the characteristic black grin patch on the bill of that species. This birds legs and bill are also orange, not the pinkish we would expect on a Snow Goose. So, we can probably rule that species out, as we can the smaller but fairly similar Ross's Goose. Maybe this bird is some sort of domestic fowl, a genetic amalgamation many generations removed from anything either pure bred or completely wild. Actually, it is a genetic anomaly, but not of the domestic sort. Based on this shot, I (and many others who have seen the bird) surmised it is a leucistic Canada Goose! Guilt by association aside, the structure of the bird fits this diagnosis perfectly (see group shot below).

Hold on, wait a minute. What does leucistic mean? And how is it different from an albino? Well, albanism is a genetic condition that results from a defect in the production of melanin. Melanin is a pigment that is expressed in pigment cells in the hair and skin (from which feathers originate) as well in the retinal cells of the eyes. It is the lack of melanin in retinal cells that causes the characteristic pink-eyed phenotype. Importantly, the normal pigment cells are present, but they are defective in melanin production. The pigment cells in the hair and skin are still fully capable of producing other pigment types, so albinos can sometimes appear yellowish due to the normal production of these other pigments.

Leucism, on the similar but other hand, results from a lack of the pigment cells themselves. This means that little to no pigment is produced in the hair or skin of leucistic individuals. The eyes aren't affected in leucism as the retinal cells are present and still capable of producing melanin. Make sense? Maybe? Even as a seasoned geneticist, I have difficultly with this! I am willing to bet that loyal blog reader Greg B will have something to say about this. Hopefully he can clarify anything that is confusing. Be sure to check in on the comments section at a later date to see if he chimes in!

Over the years I have seen many partially leucistic birds. Though the above goose is a great example of the condition, this Piping Plover that I photographed on Plum Island, Massachusetts a few years back is the single best example of leucism I have seen! 

I first observed this bird as it flew in off the ocean. As it wheeled towards the beach, I almost soiled myself. I though I had found something of the 1st-North-American-record sort. I was going to be a MassBird legend! Once it landed,  I realized that I was looking at genetic rather than geograpahic rarity. In some respects, this individual is as rare as it gets, inside or outside the bird's normal range. I was stoked to grab a few nice shots of the little guy before he resumed his oceanic trajectory. One for the archives for sure!

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