Female cuckoos tend to invade other species’ nests and, to camouflage their own eggs, they lay eggs that look strikingly similar to those that belong to that specific nest, according to a new study.
Researchers have been trying to figure out how female cuckoos are able to lay eggs with different colours and patterns, depending on which foreign nest they lay them in, so that the gullible host birds cannot tell the difference between the cuckoos’ eggs and their own eggs.
A team of scientists at the Norwegian University of Science and Technology (NTNU) has found that there is a gene determined by the female cuckoos, which helps the birds lay blue eggs. The cuckoos are a family of birds that includes the common or European cuckoo, malkohas, couas, coucals, roadrunners, koels, and anis. Coucals and anis are sometimes viewed as distinct families.
Frode Fossøy, lead author of the study and a research scientist in the Department of Biology at the Norwegian University of Science and Technology, said that the biggest mystery was how the birds managed to mimic the patterns and colours of the eggs of the host species.
Similarly to the X and Y chromosomes found in mammals, birds have Z and W chromosomes. Females have ZW and males have ZZ. According to the researchers, the gene for blue eggs could be carried by the Z chromosome, or it could also be that it is passed on in mitochondrial DNA (passed on only by mothers).
For the new study – published in the journal Nature Communications – the researchers focused mainly on the gene for blue eggs and not other colours. However, they also looked at other egg samples, even some that were about one hundred years old.
Blue eggs likely originated about 2.6 million years ago in Asia. The researchers said that in Europe, blue eggs can be found in pied flycatcher (Ficedula hypoleuca) nests, redstart nests, wheatear and whinchat (Saxicola rubetra) nests. Cuckoos try to fool some bird species by placing their own blue eggs in the host birds’ nests.
That being said, sometimes things do not go according to plan for the cuckoos, because the host birds find out that the eggs are not theirs and then kick them out and destroy them. Even though the cuckoos’ eggs evolve to resemble the hosts’ eggs more, the host birds also become better at recognising the intruding eggs and ejecting them from the nests, according to Fossøy. Currently, the population of host birds is declining all across Europe, and, as a result, so are the cuckoos, he explained.
Fossøy and his colleagues will conduct further research over the next couple of years to also study other egg colours and patterns. Because the blue coloured eggs had been studied a lot more, they were ideal for the new study. The research team form the Norwegian University of Science and Technology has already sequenced the genomes of several cuckoos. However, more data in needed to find things about the other coloured eggs, researchers said.
Image Source: nature