The amazing mimicry of the Vidua finches uncovered by University of Cambridge scientists
The astonishing mimicry of a group of finches in Africa has been uncovered by an international team of researchers, including from the University of Cambridge.
They collected images, sounds and videos over four years in the savannahs of Zambia to build up a picture of the tactics of the birds known as the indigobirds and whydahs, of the genus Vidua.
Like common cuckoos, the 19 species in this group take an absentee approach to parenting by laying their eggs in the nests of other birds.
But while cuckoos mimic their host’s eggs to enable this deception, this group of parasitic finches have evolved to mimic their host’s chicks with amazing accuracy - down to elaborately coloured patterns in their mouths.
Each species of indigobird and whydah lays its eggs in the nests of a particular species of grassfinch.
The host incubates the foreign eggs and feeds the young alongside their own when they hatch.
While most nestlings are cryptically camouflaged to avoid detection by predators, grassfinches are unusual in having brightly coloured and distinctively patterned chicks.
Nestlings of each grassfinch species have their own unique appearance, begging calls and movements.
The ‘brood parasitic’ Vidua finches mostly exploit a single host species, making them extremely specialised parasites. They were found to mimic the appearance, sounds and begging movements of their grassfinch host’s chicks.
“The mimicry is astounding in its intricacy and is highly species-specific,” said Dr Gabriel Jamie, lead author on the paper and a research scientist in the University of Cambridge’s Department of Zoology, and at the FitzPatrick Institute of African Ornithology, University of Cape Town.
“We were able to test for mimicry using statistical models that approximate the vision of birds. Birds process colour and pattern differently to humans so it is important to analyse the mimicry from their perspective rather than just relying on human assessments.”
“Birds, for example, have an extra colour-sensitive receptor on their retinas that allows them to see in ultraviolet.”
The begging calls mimicked by the Vidua finches are as specific as the appearance.
But there were some minor imperfections in the mimicry.
It could be that there has not been sufficient time for even more precise mimicry to evolve - or perhaps there is no need for it because the current mimicry is good enough to fool the host parents.
But the researchers also think some of the ‘imperfections’ might be enhanced versions of the hosts’ signal that force the adult birds to feed the parasite chick even more than its own.
The study, published in Evolution, suggests the mimetic adaptations to different hosts could be critical in the formation of new species and in preventing species collapse through hybridisation.
Professor Claire Spottiswoode, an author of the paper and a research scientist at both the University of Cambridge and Cape Town, said: “The mimicry is not only amazing in its own right but may also have important implications for how new species of parasitic finches evolve.”
The early life experiences of Vidua nestlings have a profound impact on them, altering their mating and host preferences. This imprinting on their hosts therefore influences the host environment in which their offspring grow up, and the evolutionary selection pressures they experience from foster parents.
Over multiple generations, these selection pressures generate the amazing host-specific mimetic adaptations seen by the research team.
“I think it provides a really compelling example fo the power of natural selection to produce truly stunning adaptations,” said Dr Jamie.
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