When Dad's Not a Looker, Mom Compensates

Sept. 27, 2006 — -- It may be true that the early bird gets the worm, but it turns out that it's also true that it doesn't hurt to be the ugly bird either.

New research shows that a female house finch who gets stuck with a dull male can make up for some of his shortcomings by embedding an extra dose of hormones and antioxidants in the yolks of her eggs.

It's one of those miracles of nature that we never knew was there until a few years ago when scientists found that a female can deposit different amounts of nutrients in her eggs to give her offspring a better chance at survival.

No one's yet sure how she manages to do that, but until now scientists believed the female would naturally favor eggs that had been fertilized by a male with gorgeous red plumage, because he got that color by being good at getting food, and thus would be a better provider.

"We found completely the opposite," says Kristen Navara, lead author of a report on research conducted at Auburn University, published in the November/December issue of Physiological and Biochemical Zoology.

Navara is a reproductive physiologist, and she is now a postdoctoral fellow at Ohio State University's College of Medicine and Public Health. Co-authors are Alexander V. Badyaev at the University of Arizona, Tucson, and Mary T. Mendonca and Geoffrey E. Hill of Auburn.

"There is the thought that the best-looking males potentially have the best genes, so theoretically the female would want to invest in the offspring with the best genes," she adds.

Nope.

She says her research shows that a female tries to compensate for having a dull male by doing what she can to enrich her eggs with the things the offsprings will need for growth and development. She calls it "compensatory strategy," which is "an attempt to compensate for the lower quality of a male."

That strategy seems to be working, judging by the population explosion among house finches despite the fact that they live rather hazardous lives. They like to live around people, so there's lots of things to fly into, like cars and windows and cats, and they suffer from a number of diseases, particularly pink eye.

So a female house finch really has only one or two chances to breed before her short life is over. Under the best of circumstances, house finches are "socially monogamous," although some have been known to play the field. Often, the mate from the previous season doesn't show up, so the female has to take whatever she can get.

"They don't have time to just wait for a better male to come along," she says. They have to get on with it, and sometimes the best they can do is to mate with a male with yellow plumage, the mark of a lackluster performer when it comes to feeding the brood.

Navara and several colleagues were in a perfect setting to find out what happens next. Auburn University has more than 150 nesting boxes scattered around the Alabama campus, mostly occupied by house finches. The researchers were able to capture and tag all the males, so they could monitor who was doing what to whom.

Each time the female laid an egg, the researchers removed it and replaced it with a clay egg, tricking the female into continuing to lay more eggs. The yolks were extracted from the eggs and checked for composition and antioxidants.

The results, she says, were conclusive. The females who had mated with the yellow males produced eggs that were much richer in nutrients than those who had mated with the handsome, red males.

The question still remains, though. How does she do that?

"It's not that she thinks about it," says Navara. "But there's some mechanism that allows her to deposit different amounts into different eggs, based on a bunch of different criteria, in our case the male color."

As noted above, it seems to be working. Until the 1940s, house finches were found in Mexico and the southwestern United States. But some joker exported them to New York, where they were marketed as "Hollywood finches." That's apparently because of their colorful feathers, not their marital fidelity.

Anyway, as the story goes, it was against the law to sell the birds, so some pet stores released them into the wild. They had a tough time at first, but within a few years had adapted to a very different climate and expanded their range as far west as the Mississippi River. Today they're found all over the place.

And that probably took a lot of compensating, since some males are beautiful, and some a bit drab. That left it up to the females to make up the difference.

All of which proves, once again, that Mom really does know best.