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Cheats of the bird world -- Cuckoo finches fool host parents

University of Exeter

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IMAGE: This is a cuckoo finch chick. view more

Credit: Claire Spottiswoode

Cuckoo finches that lay more than one egg in their victims' nests have a better chance of bamboozling host parents into fostering their parasitic young, a study has found.

Dr Martin Stevens from the University of Exeter and Dr Claire Spottiswoode from the University of Cambridge, with Dr Jolyon Troscianko at the University of Exeter, demonstrated that when African cuckoo finch females lay more than one egg in the same nest of their African tawny-flanked prinia hosts, the foster parents find it harder to tell their own eggs from the imposter's.

The host is therefore less likely to reject the parasite's eggs, such that the parasitic chick is raised for free at the host's expense. This helps to explain why female cuckoo finches commonly lay more than one egg in the same host nest.

Host parents often have difficulty in distinguishing parasitic eggs from their own because cuckoo finches lay eggs that beautifully mimic those of their hosts. Such mimicry has evolved to combat egg rejection by picky parents who remove foreign eggs from their nests.

Egg rejection depends on hosts accurately discriminating parasitic eggs from their own. To do so they must first carry out the sensory task of detecting small differences in egg colours and patterns between their eggs and the parasite's. They must then also correctly identify which eggs are parasitic, to ensure that they don't mistakenly reject any of their own eggs. This is a cognitive task relying on an ability to process the sensory information and compare it to a memorised template of what their own eggs look like.

The presence of multiple parasite eggs in the nest causes hosts to be uncertain about which eggs belong to them and which are imposters, because these sensory and cognitive mechanisms conflict with one another.

Dr Stevens said: "Our work shows that by laying multiple eggs in each host nest, the cuckoo finch has evolved a novel strategy, in addition to egg mimicry, to defeat host defences and increase its reproductive success. Laying several eggs in a host nest causes confusion in host defences, and when combined with effective mimicry, they can outwit the hosts and help more of their young to be reared.

"In the future it would be great to know whether other brood parasites have similar strategies, and whether there is any way that hosts can fight back in the arms race against the cuckoo finch."

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The study, Repeated targeting of the same hosts by a brood parasite compromises host egg rejection, received funding from the BBSRC and has been published in Nature Communications. It can be viewed at: http://dx.doi.org/10.1038/ncomms3475

You can read more about the team's work at: http://www.sensoryecology.com and http://www.africancuckoos.com

For further information:

Martin Stevens (University of Exeter, Penryn, UK)
Mobile: +44 7919 372434
martin.stevens@exeter.ac.uk

Or

Jo Bowler
University of Exeter Press Office
Office: +44 (0)1392 722062
Mobile: +44(0)7827 309 332
Twitter: @UoE_ScienceNews
j.bowler@exeter.ac.uk

About the University of Exeter

The Sunday Times University of the Year 2012-13, the University of Exeter is a Russell Group university and in the top one percent of institutions globally. It combines world-class research with very high levels of student satisfaction. Exeter has over 18,000 students and is ranked 7th in The Sunday Times University Guide, 10th in The Complete University Guide, 10th in the UK in The Times Good University Guide 2012 and 12th in the Guardian University Guide 2014. In the 2008 Research Assessment Exercise (RAE) 90% of the University's research was rated as being at internationally recognised levels and 16 of its 31 subjects are ranked in the top 10, with 27 subjects ranked in the top 20.

The University has four campuses. The Streatham and St Luke's campuses are in Exeter and there are two campuses in Cornwall, Penryn and Truro. In an arrangement that is unique in the UK, the Penryn Campus is owned and jointly managed with Falmouth University. At the campus, University of Exeter students can study programmes in the following areas: Animal Behaviour, Conservation Biology and Ecology, English, Environmental Sciences, Evolutionary Biology, Geography, Geology, History, Human Sciences, Mathematics and the Environment, Mining and Minerals Engineering, Politics and International Studies, Renewable Energy and Zoology.

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