The earlier that birds pair, the better they fair

23 December 2020

New research from the University of Oxford, published today in Proc. R. Soc., finds that great tits who meet their future ‘spouses’ earlier in the year are more likely to be successfully when it comes breeding, but that these well-acquainted pairs are just as likely to divorce as pairs that meet closer to the breeding season.

A team of researchers at the Edward Grey Institute, Department of Zoology, Oxford studied great tits in Wytham Woods, Oxford. The researchers used miniature tracking technology to record when individuals first met their future partners, and then monitored the nesting attempts of 383 tracked pairs of birds.

They found that individuals who meet their future partners earlier on in winter are more likely to breed earlier in the spring and subsequently more successful in raising their offspring compared to individuals who meet their future partner with less time to go before the breeding season.

Using statistical models, the researchers show the increased breeding success of these pair-bonded individuals is actually an indirect consequence of their early meeting – whereby earlier laying pairs laid more eggs, and their young then had higher hatching and fledgling success.

Interestingly, there was no direct influence of the length of the initial pairing period on the likelihood that a couple would remain together, or ‘divorce’ after their first breeding. While it’s difficult to pinpoint the exact moment these couples became a pair, evidence shows that the more familiar they are before the breeding season, the more successful their partnership will be. This is known as the ‘mate familiarity effect’, as familiar partners have improved coordination, cooperation, and responsiveness – as with humans, the more we know about how to care for our partners, the better we are at it.

The study used fine-scale tracking technology to gather six years’ of data on pre-breeding social associations of individually marked great tits, and spring breeding data from the same.

Dr Culina says: ‘It is so amazing that we have all this technology today, so we can learn what happens with these little birds and their relationships as they forage in winter flocks. Most of what we know about partnership in birds comes from the breeding season, but we are becoming increasingly aware that time before breeding plays an important role in pair dynamics of socially monogamous species, as our study shows.’

Written as a combination of Dr Antica Culina’s PhD thesis at Oxford and her current research project at NIOO-KNAW, this is only the third study on the influence of relationship length on breeding success, and the first to have been carried out on a wild population.

Notes to Editors

For further information, please contact Dr A Culina: [email protected].

‘Familiarity breeds success: pairs that meet earlier experience increased breeding performance in a wild bird population’ will be published in Proc. R. Soc. B20201554

Image caption: Great tit; copyright NIOO-KNAW, photo credit Koos Dansen.

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