Scandal and intrigue in suburbia

On the Pull Researcher/Interpreter Gayle Dower explores the scandalous world of blue tit courtship in her research on the Natural Science Collection.

Blue tit case, bcmas000003
Blue tit case, bcmas000003

Blue tits are cute little monogamous birds, right? Every spring males establish territories, agreeing real estate by squaring up in song, and if they’re lucky attracting a lovely female each, whereupon they live happily ever after, right? Wrong, very very wrong.

For a start, they’re all having affairs as soon as their partner’s backs are turned. For any given clutch of eggs, chances are there’s at least two fathers.

You can still call blue tits socially monogamous, that is, they live in pairs while breeding, and cooperate to bring up the young in their nest. But they certainly are not genetically monogamous.

Which means the choices blue tits make when finding a partner are a lot more complicated than previously thought, for both females and males.

The Older Man

Detail of blue tit case, bcmas000003
Detail of blue tit case, bcmas000003

A truly dreamboat mate for a blue tit girl would be an older man who, for his age, has a bright crown which blue tits can see in the ultra violet spectrum. He also sings long and loud to show he’s still got it, and provides plenty of food during courtship and beyond, whether through effort or skill, which shows that he’s more experienced at finding food. Even though, given how he’s such a catch, he probably would be mating with a number of other females on the side.

She might temper it a bit with the odd dalliance herself, just to make sure she’s got a mix of genes (which makes good evolutionary sense), but not too much. She doesn’t want to risk being caught, or dad might be less inclined to help at home, and anyway, she’s got a great bloke already.

But as there’s never enough of these amazing males to go round, females have to trade off the different qualities, and do the best they can, maybe even balancing good traits in one’s spouse against good traits in affairs.

Not surprisingly, with so many qualities to choose between, different studies come to different conclusions as to what is important to females. Overall age is perhaps most important, females seem to be more faithful with older males.

Wonder woman

And what are males looking for in females? Well, most females are going to produce about the same number of eggs. A healthy female will probably produce healthier eggs, and older females will probably do better at raising chicks. So, in an ideal world, a male wants his mate to be as healthy a bird as he can get and if possible, more mature.

But apart from the fact that any given male isn’t necessarily going to get one of these wonder women, from a male point of view, differences in quality is less important than differences in quantity.

If he can be sure that his missus is being faithful, and that his nest contains his babies, then putting loads of effort into raising them is a good way to ensure his genes get through to the next generation.

However, even then there’s no harm in maybe trying to get a few more kiddies out there by mating around a bit. Mind you, he can be sure every other male’s doing the same. So then there’s a bit more doubt about those chicks in the home nest. Basically as a male’s doubt goes up about his own nest, his effort should switch from feeding at home to getting laid elsewhere. But he can’t waste too much time trying to find the best females for his dalliances, as he’s got mouths to feed back home and that’s still important as some of his nest should at least be his. Go too far neglecting fatherly duties for random mates and none of the babies in his nest will make it and given that, unless he’s pretty hot, probably the neighbouring females aren’t going to be too interested either then he may blow it completely, he’s got to find a balance.

Double crossing duo

So the rule females are following is: find the best male she can as a partner with the sub-rule, depending how good hubby is, try to find really good males for affairs and risk getting caught. Meanwhile males follow a different rule: find the best female they can as a partner, plus as many females as possible for affairs, while still feeding wife and family enough to survive with sub-rule if partner cant be trusted, invest even more energy in having affairs and less in feeding marital nest.

One thing is clear, when you see a pair of blue tits trekking back and forth to their nest from your bird table, taking turns to feed their little ones, don’t be deceived. You’re not witnessing a picture of perfect family harmony, rather the tip of a seething mass of intrigue and double-crossing, the battle of the sexes played out in miniature.

Other scoundrels of the garden

And, just in case you think they’re the only scoundrels of the garden, it’s not just blue tits. Great tits are just as bad, though they’ve been less studied, we know they too have lots of affairs and that females seem indecently interested in the male breast stripe.

Female dunnocks often play off more than one male against each other. Actually, they’re a pretty randy species across the board and males and females will both practically mate with whoever is in their territory
And if you want truly unsavoury, pity the poor female sparrows – every time she goes off to feed she risks being gang-raped by males, even if she takes her mate with her as protection. Meanwhile male wrens build lots of nests and attempt to attract more than one female to set up home. Quite a few succeed and live a happy bigamist existence!

References

Bart Kempenaers, G. R. Verheyen, M. Van Der Broeck, T. Burke, C. Van Broeckhoven & A.A. Dhondt. “Extra-pair paternity results from female preference for high-quality males in the blue tit”. Nature, Vol. 357 (1992), pp 494-496.).

Cecilia Kullberg, David C. Houston & Neil B. Metcalfe. “Impaired flight abilitya cost of reproduction in female blue tits”. Behavioral Ecology Vol. 13, No. 4 (2002), pp 575579.),

Angelika Poesel ,Hansjoergp.Kunc, Katharina Foerster, Arild Johnsen & Bart Kempenaers. “Early birds are sexy: male age, dawn song and extrapairpaternity in blue tits, Cyanistes (formerly Parus ) caeruleus” Animal Behaviour, Vol. 72 (2006), pp 531-538.).

Kaspar Delhey, Anne Peters, Arild Johnsen & Bart Kempenaers “Seasonal changes in blue tit crown color: do they signal individual quality?” Behavioral Ecology, Vol 17, No. 5 (2006), pp790-798. and testosterone level

Anne Peters,~Kaspar Delhey, W.~Goymann & Bart~Kempenaers. “Age-dependent association between testosterone and crown UV coloration in male blue tits (Parus caeruleus)”. Behavioral Ecology and Sociobiology, Vol.59, No. 5 (March 2006). pp 666-673

A. Dreiss, M. Richard, F. Moyen, J. White, A.P. Møller, & E. Danchin. “Sex ratio and male sexual characters in a population of blue tits, Parus caeruleus”. Behavioral Ecology, Vol. 17 (2006), pp 13-19..

Kaspar Delhey, Arild Johnsen, Anne Peters, Staffan Andersson & Bart Kempenaers. “Paternity analysis reveals opposing selection pressures on crown coloration in the blue tit (Parus caeruleus)”. Proceedings of the Royal Society of London B, Vol. 270 (2003), pp 20572063, and also seem to prefer older males for affairs Angelika Poesel ,Hansjoergp.Kunc, Katharina Foerster, Arild Johnsen & Bart Kempenaers. “Early birds are sexy: male age, dawn song and extrapairpaternity in blue tits, Cyanistes (formerly Parus ) caeruleus” Animal Behaviour, Vol. 72 (2006), pp 531-538.

Also:
Kaspar Delhey, Arild Johnsen, Anne Peters, Staffan Andersson & Bart Kempenaers. “Paternity analysis reveals opposing selection pressures on crown coloration in the blue tit (Parus caeruleus)”. Proceedings of the Royal Society of London B, Vol. 270 (2003), pp 20572063

Anne Peters,~Kaspar Delhey, W.~Goymann & Bart~Kempenaers. “Age-dependent association between testosterone and crown UV coloration in male blue tits (Parus caeruleus)”. Behavioral Ecology and Sociobiology, Vol.59, No. 5 (March 2006). pp 666-673

S. Andersson, J. Örnborg & M. Andersson. “Ultraviolet sexual dimorphism and assortative mating in blue tits.” Proceedings of the Royal Society of London B, Vol. 265 (1998), pp 445-450

S. Hunt, I.C. Cuthill, A.T.D. Bennett & R. Griffiths “Preferences for ultraviolet partners in the blue tit.” Animal Behaviour, Vol. 58 (1999), pp 809-815.

Information on the suggested additional garden birds can be found in:

Robert Burton, Garden Bird Behaviour: How to recognise and interpret everyday bird activities. The Wildlife Trusts Series.(London, New Holland Publishers (UK) Ltd, 2005). pp.87-91

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