The stress of having an unattractive partner

Here’s how blog writing usually goes for me: I peruse science journals for a suitable story, read a few articles, pick one, write the blog post, copy the reference, and find a good picture. Then I spend anywhere from an hour to a couple of days trying to come up with a title. For some reason, finding the right title is always the hardest part. So this week, when I saw an article with a title that I could use as is for the blog post, I just knew I had to write about it.

The article, as you can infer from the title of this post, looks into the relationship between attractiveness of a mating partner and stress in female birds. Most birds, like humans, tend to form monogamous pair bonds that last through the course of at least one reproductive event. Because of this “socially monogamous” system, if there are approximately the same amount of males and females around, most birds will be able to find a partner, but inevitably, a big chunk of females will end up paired with males of “below-average” quality (but I’m sure they have lovely personalities). So the researchers wanted to know, how does that make the female birds feel?

As I’m sure you can imagine, rating the attractiveness of one bird over another is no easy feat for human scientists. What’s more, beauty is in the eye of the beholder, but you can’t send out mass emails to female finches to fill out online in their spare time (“On a scale of 1 to 7, 1 being Dwight Schrute and 7 being George Clooney, how would you rate Mr. John Finchy?”). Therein lies the beauty of this study: the researchers picked a very creative model to answer their question. They studied a type of finch that comes in two colors: red heads and black heads. Even though they are the same species, red-headed and black-headed finches are partially genetically incompatible (meaning they have a harder time producing offspring), and so these birds tend to have a preference for mating partners with the head color that matches their own (though if there are slim pickings, they will mate with a bird of the other color). Knowing this, the researchers set up an aviary with a whole mix of these birds (males, females, in combinations of red heads and black heads) that had not previously met, waited until every bird had paired off, and then assessed the females’ satisfaction with their mating partner based on two parameters: how long until she would agree to breed, and how much corticosterone (a stress hormone) she had in her blood (don’t worry, a harmless procedure).

The results show that females that paired with a male of the wrong color laid eggs nearly one month later that the females paired with a male of the same head color. What’s more, females paired with incompatible (“below-average” quality) males had three to four times more stress hormones in their bloods, and this went on for weeks. Who knew that attractiveness could have such an impact on stress levels?

As it turns out, a widespread strategy used by female birds to deal with unattractive mates is to… select alternative, extrapair fathers for their offspring. Dan Savage would have a field day if he knew about these little sneaky females…


Constrained mate choice in social monogamy and the stress of having an unattractive partner. (2011) Griffith SC et al. Proc. R. Soc. B [Epub ahead of print].