Australian cuckoo birds have taken a
new evolutionary step ? mimicking the colour 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 colour 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 colour 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 coloured young, ranging from black, to yellow, to
pink.
The paper, ?Visual mimicry of host nestlings by cuckoos? is
published in the current issue of the
Proceedings of the Royal Society
B. A copy is available from the ANU media office.
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