You’re at a party and you’re single. Unfortunately, so are most of your friends, and they have already paired up with the most attractive people in the room. Do you try your chances with the ones who are left, even though you don’t really like them?
Animals face these sorts of decisions all the time. For example, the vast majority of birds stay with their mates for at least one breeding season. Some even mate for life. None of them have an infinite choice of mates, and some individuals will inevitably end up with an inferior partner. And according to Simon Griffith from Macquarie University, that can be a very stressful experience.
Griffith worked with the stunning Gouldian finch. It’s hard to think that any bird so beautiful could be unattractive but even for them, looks matter. The birds have either red or black heads, and all of them prefer to mate with partners that share the same colour. If a mixed pair gets together, their chicks are 40-80% more likely to die early. So for a female, it pays to be choosy about her mates.
Griffith set up a mass speed-dating event by introducing large groups of Gouldian finches, all strangers, into six aviaries. Eventually, they all paired up and settled down in a set of next boxes. If females ended up with males of the opposite head colour, they laid their first egg nearly a month later than those who landed a male with the same colour. Their blood also contained around three times as much corticosterone, a hormone produced in stressful situations.
If Griffith forced the females into arranged partnerships with specific males, he found the same thing. Females who were saddled with unattractive males laid their eggs later and had more corticosterone. Griffith found that their hormones spiked just 12 hours after they met their partner and stayed high for several weeks. The speed of the spike suggests that the male didn’t do anything to boost the female’s hormones. She was just reacting to his presence.
Griffith writes, “These females are making the best of a bad situation and are dissatisfied with their partner although he does represent a better option than not breeding at all.” So why feel stressed about it? Here, it would be too easy to anthropomorphise the birds, by picturing them sulking in their nest boxes. But remember that Griffith measured the levels of a hormone; he didn’t interview the birds about their emotions.
Griffith thinks that a surge of stress hormones could actually help the finches. Stressed animals often put less effort into reproduction. After all, when conditions are tough, it might make sense to focus on surviving rather than breeding. And if finches are stuck with an incompatible partner, they could also benefit from belaying their resources until they find a better one. The hormones could even affect a female’s behaviour, making her more likely to seek out a better partner for some sneaky sex on the side. A female who’s stuck with a poor male isn’t out of options.
Reference: Griffith, Pryke & Buttemer. 2011. Constrained mate choice in social monogamy and the stress of having an unattractive partner. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.2672
Images by Arjan Haverkamp and Snowmanradio
More on sexy birds:
February 3rd, 2011 at 10:12 am
“If females chose males with the same head colour, they laid their first egg nearly a month earlier than those who were stuck with an oppositely coloured male. Their blood also contained around three times as much corticosterone, a hormone produced in stressful situations.”
Same color and more stress? Shouldn’t that be less stress? Or I might be reading it wrong.
[D'oh! Fixed. Thanks - Ed]
February 3rd, 2011 at 10:49 am
One more fix needed. Now all females seem to be with opposite males. “If females ended up with males of the opposite head colour, they laid their first egg nearly a month later than those who were stuck with an oppositely coloured male.”
Which got to be with males of the same head colour?
Do males help rear chicks? If female stress level affects more than just egg laying date and also affect female care of the chicks, perhaps the males with opposite headed females could compensate and increase their attention to the chicks. (Or do they get stressed too?)
Thanks for the write up. Now I’ll have to go read the original article.
February 3rd, 2011 at 11:44 am
“If females ended up with males of the opposite head colour, they laid their first egg nearly a month later than those who were stuck with an oppositely coloured male.”
Shouldn’t the first “opposite” be replaced by “same”?
February 3rd, 2011 at 12:06 pm
Arrg goddammit. Okay all of those problems should now be fixed. Look, just everyone stare at teh pretty birds, okay?
February 3rd, 2011 at 1:53 pm
I haven’t read the full paper, but isn’t this suggestive of incipient speciation? – if mates from the different color morphs are producing fewer viable offspring. Not that the changes in hormone levels aren’t interesting in this situation – and it might be one of the proximate mechanisms enforcing correct mate choice and pushing toward speciation.
February 3rd, 2011 at 6:52 pm
After reading this, into my head popped recollection of James Carville’s strategy for successfully picking up women in bars: “Go ugly early.”
He said that while sitting with his wife, on network television. Glaring ensued.
February 4th, 2011 at 12:04 am
Hey thank god there’s spermbanks, AI or just staying single in advanced developed nations.
February 6th, 2011 at 4:41 am
How do the birds know what colour their own heads are? Or is the preference based out of genetic predisposition? if so, I’d agree with aki’s suggestion the hormone levels and survival rates are more related to speciation.
February 9th, 2011 at 1:03 am
Interesting, agree with Aki and Tim, there might be some speciation goin’ on. if it is, it’s the first time i’ve heard of appearances being a driving force for it. (not that i’m that familiar with speciation or evolution)
this is such a fun post, and it sounds remarkably similar to some of the rom-coms out there.
“Griffith found that their hormones spiked just 12 hours after they met their partner and stayed high for several weeks. The speed of the spike suggests that the male didn’t do anything to boost the female’s hormones. She was just reacting to his presence.”
guess it’s not just humans who are shallow. lol.