Socially monogamous birds more promiscuous than previously thought

What gets you out of bed in the morning? Before morning has broken, and some time before blackbird has spoken, songbirds rise for sex. And a clever new experiment reveals just how important it is for male songbirds not to sleep in.

A great many species of songbirds nest in pairs, presenting to the world a facade of monogamy. Until the 1990's, songbirds were rhapsodised by social conservatives as paragons of family values, mother and father working together faithfully to fledge their demanding chicks. Until new genetic technologies revealed that most socially monogamous birds were playing a lot of away games.

For a long time, ornithologists failed to spot the shennaniganising because most of it happens just before dawn, when even the hardiest birdo is still rubbing sleep from their eyes. That's actually a bit unfair: ANU's Professor Andrew Cockburn and his many collaborators have risen unspeakably early for decades to study Australia's superb fairy wrens, revealing them to be Olympic medallists of extra-pair sex. Female wrens leave the nest before dawn, heading straight to males singing in the dawn chorus.

This kind of behaviour gives male birds two reasons to rise early: to prevent their social mate from mating with another male, and perhaps to get a little bit on the side from some other male's social mate. European blue tit males who start singing early in the morning sire more chicks with other females, chicks he doesn't have to raise because the female and her social mate do all the heavy lifting.

Consequences

But how do early and late risers do with their social mates? A team based at the Max Planck Institute for Ornithology in Radolfzell, Germany, found an ingenious way to answer this question.

By inserting slow-release melatonin implants beneath the skin of free-living male Great Tits, just before the breeding season, they tweaked the birds' circadian rhythms. The body releases the hormone melatonin at night, and animal circadian activity patterns are cued by melatonin levels. Nocturnal animals are stirred into activity and dirurnal animals to sleep by rising melatonin.

Male great tits in the control group became active about 22 minutes before dawn, but those with melatonin implants took an extra ten minutes to get going. They were no less active during the day, and they stopped for the night at the same time, a few minutes before dusk.

But those extra ten minutes cost the males dearly. Twelve percent of chicks fledged from the nests of control males were sired by another male, but 42 percent of chicks in the nests of melatonin-implanted males had been conceived with another male's sperm.

As an early riser, I'd like to claim victory for the early birds at this point. But of course I can't. For humans, Sex at Dawn remains niche. Many even prefer to rise early for bird watching.

The night time is where the action is for our species. Night owls tend to be more extrovert, novelty-seeking, and night-owl men (but not women) report having more sexual partners. Night-owls are more likely than early risers to be single and open to short-term commitment-free sex. Being a night owl is associated with risk-taking in women on a levels similar to males (both night-owls and early risers). Risk-taking predicts short-term sexual behaviour, suggesting that female night owls might be especially oriented toward sex.

Interesting, it's true, but not yet the basis for any firm prescriptions. Unless you're Charlotte Alter writing at Time Magazine. Anybody spot the implicit bias and rampant earlybirdophobia?

Women who stay up late are more likely to get laid, but less likely to get married than women who get up early to do a sun salutation or whatever.

Whatever indeed!

This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).