Birds on the Gold Standard

Another find from the Starved Rock feeders:

American Goldfinch (Spinus tristis), Starved Rock State Park,
La Salle Co, IL 1/26/2014

This is a male American Goldfinch (Spinus tristis). That yellow on the face is a precursor of things to come. If he's still around in July, he'll look like this:

American Goldfinch, Illinois Beach State Park,
Lake Co, IL 7/27/2013

This is an abundant species found across the entire lower 48, so it's not surprising it's been used often as a test subject. Given the intense color of the males, and the fact that it's based on dietary carotenoid pigments and is therefore easy to manipulate experimentally, it's also not surprising that much of the work done on these guys looks at sexual selection.

Johnson, et al. found that females do show preferences for brighter colors, including not just yellow pigment but the orange bills that particularly bright males show (1). They further showed that birds sporting orange leg bands were favored. (This may well be an interesting side effect of studies that color-band birds to be able to ID individuals in the field.)

Rosen & Tarvin demonstrated that differences in body plumage and bill brightness correlated well with body condition in males, and that bill color could change rapidly in captive males, suggesting that bright colors in this species actually do signal phenotypic quality, both short and long term (2).

Finally, MacDougall & Montgomerie demonstrated that American Goldfinches mate assortatively by color*,  suggesting that in addition to the expected female choice-based sexual selection, males may be actively choosing their mates as well. They further suggest that this may serve to maintain genetic variation in goldfinch populations. (3)

What is surprising is that very little of this sort of work has been done on Lesser (S. psaltria) or Lawrence's Goldfinches (S. lawrencei). They are both closely related, and Lessers are quite common across the southwestern US. (Lawrence's are not so common, mostly in California, which probably goes a long ways towards explaining that particular lack of interest.) This may be a case of closely related species handling the experimental manipulations (i.e. captivity, dietary changes) in very different ways, but I suspect that this is the same process that produces other model organisms. One common species gets a majority of the early work, and then new investigators build on the work that's already been done. With every paper that's published on American Goldfinches, it gets harder to jump to Lessers. Any question you're in a position to ask about Lesser has already been examined in Americans, and the expectation is that you won't learn anything really new.

This is a natural process, and it does result in some very detailed knowledge of those creatures that receive such scrutiny. (E. coli, Arabidopsis, C. elegans,...) But how much are we missing by assuming that our models are somehow typical for their groups? The only way to find out is to start to branch out into those lesser-known species. So here's a little plea for all those understudied critters.

*i.e. bright males tend to end up with bright females.

(1) Johnson, K., Rosetta, D., & Burley, D. N. (1993). Preferences of female American goldfinches (Carduelis tristis) for natural and artificial male traits. Behavioral Ecology, 4(2), 138-143.

 

(2) Rosen, R. F., & Tarvin, K. A. (2006). Sexual signals of the male American goldfinch. Ethology, 112(10), 1008-1019.

 

(3) MacDougall, A. K., & Montgomerie, R. (2003). Assortative mating by carotenoid-based plumage colour: a quality indicator in American goldfinches, Carduelis tristis. Naturwissenschaften, 90(10), 464-467.