Wednesday, December 1, 2010

Colorful birds get the chicks

A bright male House Finch, Carpodacus mexicanus. This guy should be a real chick magnet. Photo by John Pogacnik.

Females drive A LOT of what we males do. And not just behavior. Over the long haul, through a process known as sexual selection, the girls even can change our appearance.

At least that's the case with House Finches, and many other birds.

Sexual selection is an evolutionary bology term that speaks to the process of the development of certain traits that are driven by competition between members of one sex, in order to better attract members of the opposite sex. This, as might be expected, is much more pronounced in males.

Sexual selection was first proposed as a theory by Charles Darwin in his watershed book On The Origin of Species. In the 151 years since, scientists have taken sexual selection beyond the realm of theory, and learned much more about how the overwhelming urge to attract a mate and reproduce ultimately influences physical appearance.

The common House Finch, a songbird that now ranges far and wide across the North American continent and is abundant in Ohio, is a wonderful example of sexual selection. Male House Finches are quite variable in coloration, as anyone who has watched large numbers of them at their feeders knows. They can range from yellowish to orange to a rich rosy red, with all sorts of varying levels of intensity.

This variation in color certainly doesn't escape the discerning eye of the ladies. Geoff Hill at the University of Michigan suspected that color variation means a lot in regards to the ability of males to score with females, and designed an experiment to prove it. Using dyes, he created uber-finches that were super bright or, conversely, dimmed them down in intensity.

The result? The bright guys attracted more mates, and the females abandoned the nests of these pairings far less often than they did when dim guys were involved.

Why would female House Finches be attracted most strongly to the brightest males? Because these males tend to be better providers. They seem to be better foragers, and thus - as males help care for young - provide the nestlings with more food, upping their chances of survival. Bright colors in males also signal that they are healthy, as their coloration stems from carotenoid pigments from the food they eat. So, the brighter the finch, the better it is at finding food, which makes for a healthier bird, and ultimately a better provider for the young, in which the females invest a significant allotment of their resources to produce.

So, over the long haul, one would expect male House Finches to become increasingly colorful, as the genes of the brightest males are constantly favored in the process of sexual selection and passed along to the offspring.

I wonder what House Finches will look like in 25,000 years?


dAwN said...

Yeah.. What will they look like? Cardinals? Interesting..wonderful post as always Jim..

Anonymous said...

So Jim, are you going to start wearing only hot pink outfits from now on? Lol.

Jim McCormac said...

Glad you enjoyed the post, dawn, thanks for the comment!

"Anonymous": um, no thanks, I prefer cross-assortative mating. But really great comment. Really.

flux biota. said...

can you make a blog entry about anomolies in the bird world? I found this entry pretty interesting.

Birding is Fun! said...

Love your blog Jim and the interesting content. At what point does bright color become a liability due to increased exposure to predators? Does predation keep the color evolution more stable?

Jim McCormac said...

Glad you liked the post, Flux Biota - I'll see what I can do.

Good question, Birding is Fun, and I don't know the answer. Only time will tell, and I doubt any of us will be around long enough to see if House Finches brighten up to the level of male Northern Cardinals or beyond.

It's been estimated that Purple and Cassin's Finches split from their House Finch-like ancestor some 9.3 million years ago, and all of these species are still pretty similar.

Evolution can take a LONG time.