Question re coloration

[Enrique Patino]

I used audio to attract this bird who was close by singing up a storm. It was very aggressive defending its territory, yet it is mostly white. What can we tell about it from its coloration? Thanks in advance!
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[Doug West]

Looks like an American Goldfinch to me.

Doug

[Enrique Patino]

Looks like an American Goldfinch to me.

Doug

Obviously! ;)

Is coloration (as in full yellow - or not) affect the ability of an Am. goldfinch to secure optimal breeding territory? I guess that is what I am wondering about... Or, put another way... is it normal for goldfinches to display this sort of incomplete coloration?

thanks

[Declan Troy]

While not "normal" this type of plumage anomaly is not rare. The localized absence of normal pigment is termed leucism ( leucistic) and crops up in most species to various degrees. Birds like goldfinches rely on carotenoids for color. Birds can not synthesis carotenoids (but can modify them) so rely on dietary sources to acquire them; hence issues with food availability at the time of molt can also affect the amount and distribution of pigment. Hard to say how this would affect reproduction, it can cut multiple ways but it would not preclude breeding.

[Enrique Patino]

While not "normal" this type of plumage anomaly is not rare. The localized absence of normal pigment is termed leucism ( leucistic) and crops up in most species to various degrees. Birds like goldfinches rely on carotenoids for color. Birds can not synthesis carotenoids (but can modify them) so rely on dietary sources to acquire them; hence issues with food availability at the time of molt can also affect the amount and distribution of pigment. Hard to say how this would affect reproduction, it can cut multiple ways but it would not preclude breeding.

Thanks for your explanations. I think you are suggestion two possible explanations: 1- leucism and 2- caroteniod availability at the time of molt. I would have guessed # 1, but not too familiar with this trait in birds. What struck me is that none of the dark pigment areas do not seem affected. Would that suggest # 2 as the possible cause?

[Declan Troy]

Well, leucism is often used pretty broadly to include atypical white feathers for any reason so the diet alternative could still fall under the umbrella. In this case I would place the odds against a dietary cause but would be hesitant to try to diagnose the causative agent from a photo. I brought it just to point out that carotenoid pigments may have more pathways to problems. One can get leucism in dark feathers (there is a blotchy robin nesting up here right now). In the case your goldfinch the yellow (carotenoid) and dark (melanin) feathers get their colors from different biochemical pathways and are molted at different times of year (different food availability and hormonal state of the bird) so odds of abnormalities being expressed in both simultaneously are small.

[Enrique Patino]

Leucism is a genetic thing, while lack of carotenoid-derived pigments is a dietary thing... right?

[Declan Troy]

The distinction is not so black and white (or white and white if leucistic). In most cases where pigment is lacking you really don't know what the root cause is and there are many things in addition to genetics that can influence tissue growth. There are certainly genes with known variants that result in leucism. Carotenoid pigments in birds are generally modified from the diet based precursors so it is also easy to envision how genetic based variations of the required enzymes could contribute to color differences. There is a vibrant market for color variations in canaries and other finches. In many cases (like your bird) the pigment deficit is local (affecting only a portion of the plumage) and of unknown stability (will the bird look the same next year?) so it is unwise to make a simple diet/genetic inference.

[Enrique Patino]

awesome! thanks for the explanation. it would be great to see pictures of goldfinches of all wild color variants.

[Declan Troy]

Not a goldfinch but there have been a couple of posts in this forum showing evening grosbeaks lacking melanin. Makes for a dramatic change. I can't find the one I remembered but here is another interesting image:

http://www.birdphotographers.net/forums/showthread.php/35408-Evening-Grosbeak-partial-albino?highlight=evening+grosbeak

[Sandy Witvoet]

Yes, could be leucistic .... (sorry I'm late to the party here!) .... I had several Goldfinches going thru what looked like a really late molt in June....not sure why....but did look similar to yours.