Cuckoos evolve to fool angry birds
January 12, 2011
Cuckoos on left, respective host on right. Credit: N. Langmore

( -- Australian cuckoo birds have taken a new evolutionary step – mimicking the color of their host young to avoid certain death, according to a study by researchers from The Australian National University.
Researchers from the ANU College of Medicine, Biology and Environment focused on three species of the Australian bronze-cuckoo. Their study found that these birds have evolved so that they no longer simply lay eggs that mimic their hosts, but they also match the color of their young to avoid eviction from the nest.
Cuckoos are known for their parasitic ways. They lay their eggs in the nests of other species, leaving their young to fend for themselves. Once hatched, cuckoo nestlings evict all host offspring from the nest to ensure the maximum chance of survival.
Dr. Naomi Langmore from the Research School of Biology, who led the research team, said that the host birds are unable to identify the cuckoos’ eggs from their own, so their primary line of resistance is to kill the cuckoos once hatched.
“Field experiments have shown that nestlings that look different from host young are more likely to be rejected by host parents,” she said.
To ensure that their young survive, she added, the cuckoos have taken evolutionary steps so that their newly hatched young are the same colour as their host ‘siblings’.
“We have demonstrated that bronze-cuckoo nestlings have co-evolved to be striking visual mimics of their hosts,” Dr. Langmore said.
“Host parents will kill a parasite hatchling within the first two days of its life. But by matching the color of the host young, the cuckoos are accepted by their ‘parents’. The mimicry only lasts for eight days, which is long enough for the acceptance to occur. After that, the pin feathers appear on the body, and the young cuckoos begin to look like their own species.”
Each of the three species of cuckoo has their own choice of host bird. In turn, they have each evolved to lay different colored young, ranging from black, to yellow, to pink.
More information: The paper, ‘Visual mimicry of host nestlings by cuckoos’ is published in the current issue of the Proceedings of the Royal Society B.

Provided by Australian National University.

Scientists get bird's-eye view of how cuckoos fool their hosts (w/ Video)
April 26, 2010
Researchers are in the process of setting up the egg rejection experiment. Credit: Tim Dee

Using field experiments in Africa and a new computer model that gives them a bird's eye view of the world, Cambridge scientists have discovered how a bird decides whether or not a cuckoo has laid an egg in its nest. The finding offers unique insights into a 20 million-year-old evolutionary arms race.
Only seven groups of birds in the world have evolved as brood parasites, laying their eggs in other birds' nests, and ecologists have long been fascinated by this behaviour as an example of evolution in action.
Dr Claire Spottiswoode and Dr Martin Stevens of the University of Cambridge worked on two tropical African species, the parasitic Cuckoo Finch and one of its hosts, the Tawny-flanked Prinia.
Until recently, most work on cuckoos has been done in temperate regions - Europe and North America - where species are relatively young in evolutionary terms. In the tropics, however, the Cuckoo Finch and Prinia could have been locked together in an evolutionary arms race for up to 20 million years.
As parasites have evolved ever better manipulation of their hosts, hosts have responded with ever more refined defences to evade parasitism. As a result, the Cuckoo Finch's mimicry of host eggs is extraordinary, as is the Prinias' ability to spot the parasite's eggs.

A cuckoo finch nestles in a cisticola nest. Credit: Claire Spottiswoode

According to Dr Spottiswoode: "Prinias lay probably the most diverse range of eggs of any bird in the world, and this is likely to be an outcome of the long co-evolutionary battle with the Cuckoo Finch."
"The eggs are analogous to a bank note, in terms of the variety and complexity of markings, perhaps to make them very hard to forge by the parasite."
To find out exactly how Prinias detect the foreign eggs, Spottiswoode and Stevens set up more than 100 rejection experiments in southern Zambia, putting one Prinia egg into another's nest and waiting to see if the egg was rejected.

They also collected data to feed into a computer model to give them a bird's eye view of the world, using a spectrophotometer to measure egg colours and a digital camera to analyse the eggs' complex patterns. In the past, this kind of analysis was tackled by humans comparing eggs by eye, but human vision differs hugely from that of a bird. Birds can see ultraviolet light and because they have four types of cone in their eyes, compared with three in humans, they see a greater diversity of colour and pattern.
A cuckoo finch chick is shown on the left, with a prinia chick on the right. Credit: Claire

Spottiswoode Spottiswoode and Stevens found that Prinias are amazingly good at rejecting foreign eggs, and that they use colour and several aspects of pattern to spot the parasite's eggs. Mysteriously, however, they do not seem to use the scribbles that uniquely occur only on the Prinias' eggs. The specific traits used to distinguish foreign eggs were exactly those found to differ most between host eggs and real parasitic eggs. This suggests that natural selection is currently acting to make Cuckoo Finch eggs better mimics of their hosts', and also that Prinias use the most reliable information available in making rejection decisions. The work is published in PNAS on Monday 26 April 2010. Provided by University of Cambridge 


Cuckoo's copying an evolutionary curiosity

The nest poaching shining cuckoo lay eggs in the nests of grey warblers.

( -- A new study of brood parasitism in birds has shown that the nest-poaching New Zealand shining cuckoo's ability to mimic its grey warbler host is an evolutionary curiosity. A doctoral study by biologist Michael Anderson, from the University's Institute of Natural Sciences at the Albany, highlights an example of a departure from co-evolution - a common explanation for to explain apparent similarities in the calls of host and parasite birds. The migratory shining cuckoo lay eggs in the nest of grey warblers and the cuckoo chick that hatches will then push from the nest any unhatched eggs or young chicks of the grey warbler. Having disposed of the competition, the cuckoo hatchling then mimics the sound of grey warbler chicks in order to be fed by its surrogate parents. Mr Anderson's study is the first in-depth New Zealand research into the behavioural dynamics of the relationship between the shining cuckoo (pipiwharauroa or Chrysococcyx lucidus) and the grey warbler (riroriro or Gerygone igata). He used a new data analysis method for detecting co-evolution to show how cuckoo nestlings adapt their "begging" calls for food to resemble that of the warbler, which accepts the egg and raises the young as its own. What remains a mystery is how the lone cuckoo hatchling produces a grey warbler hatchling call when there are no chicks left alive to emulate. When mature, cuckoos and warblers make entirely different sounds to each other. In a co-evolution scenario two species reciprocally evolve in response to each other in what has frequently been termed an "evolutionary arms race." Contrary to the co-evolutionary model, the shining cuckoo has developed shoskills wn its prowess as an artful mimic, over-riding its biological distance from the warbler in order to trick it into surrogate parenthood, while, while the grey warbler does not appear to have altered its begging call at allresponded. In his research - carried out mostly at Tawharanui Regional Park north of Auckland - Mr Andersonhe recorded the begging calls of nestlings from 20 native forest birds found in the North and South Islands and analysed their sound properties. He found that those species that sounded more similar to each other were typically more closely related. However, the shining cuckoo appears to have altered its begging call, in order to match its host, the grey warbler, despite not being as closely related to it as other birds are. The grey warbler is New Zealand's smallest bird by weight, just 6.5g at maturity, while the shining cuckoo grows to 25g, about the same as a sparrow. Mr Anderson also studied the begging and alarm calls of the grey warbler. These form an intricate communication system between hatchlings and foraging parents. "While approaching the nest, parents tell their chicks that it is safe to beg for food," he says. "Parents also use alarm calls to tell their chicks when to be quiet when potential predators are nearby, making it more difficult for them to find the nest." As part of his study, he travelled to Hungary to examine the aggressive behaviour of the naked, blind common cuckoo hatchling, which evicts host great reed warbler eggs from the nest. He found that the egg-tossing invader suffers a temporary growth delay as result of the immense energy required to fulfil its conquest of the host nest. But the hatchlings eventually grow to normal size. Mr Anderson, who graduates on April 13, has had his research widely published. It has contributed to the well-established songbird research led by Associate Professor Dianne Brunton, who heads the institute's Ecology and Conservation group. Provided by Massey University 

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WildLife Rules!: Cuckoos
WildLife Rules!
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