From: Allison Winter, ENN
Published September 24, 2013 01:16 PM

Cuckoo Finches Trick Host Parents into Raising their Young

Brood parasitism is found among bird, fish, and insect species and involves the manipulation and use of host individuals to raise the young of the brood-parasite. Who knew the animal kingdom had foster parents and free babysitters?

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Species do this in order to relieve themselves from parental responsibilities like rearing young, building nests, or spending more time foraging for food. The concept also plays true to the adage "don't put all your eggs in one basket," in the sense that by separating your eggs, there is less of a risk if a predator were to enter the situation.

While you might think you should separate all of your eggs, a new analysis finds that by laying more than one egg in the victim's nest, Cuckoo finches have a better chance of fooling host parents into fostering their parasitic young.

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.

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. Not only do the hosts have to distinguish egg colors and patterns, but also the different sizes.

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."

The study, Repeated targeting of the same hosts by a brood parasite compromises host egg rejection, has been published in Nature Communications.

Read more at the University of Exeter.

Nest image via Shutterstock.

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