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These birds have been singing the same songs for over a million years

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The soundtrack of East Africa's "sky island" mountains a million years ago may have been very similar to what it is today. That's because, according to a new study, a group of tiny, colourful birds has been singing the same tunes for more than 500,000 years — and possibly as long as 1 million years.

Sunbirds, members of the Nectariniidae family, are brightly coloured, tiny nectar-feeding birds that look like hummingbirds and are found throughout Africa and Asia. They are the "little jewels that appear before you," according to senior author Rauri Bowie, a professor of integrative biology and curator at the University of California, Berkeley's Museum of Vertebrate Zoology.

The eastern double-collared sunbird (Cinnyris mediocris), also known as the "sky island sunbird," lives on the peaks of tall mountains from Mozambique to Kenya. For tens of thousands to a million years, these skyscraping peaks have isolated different populations, or lineages, of this species from one another. Despite this, many populations of sky island sunbirds are indistinguishable from one another.

Bowie and his colleagues wondered if the birds' songs had remained unchanged over the aeons. To answer this question, the researchers visited 15 different sky islands in East Africa between 2007 and 2011, recording the songs of 123 different sunbird lineages. They then devised a statistical method for analysing how the sunbirds' songs changed over time.

It turns out that some of these isolated populations continue to sing the same songs. This suggests that these songs haven't changed much in the thousands of years since these lineages split. According to the statement, the researchers discovered that the two populations of species that had been separated the longest had nearly identical songs, whereas two other populations that had been separated for a shorter time had very different songs.

Biologists typically expect bird songs to evolve and change over time in different populations, so the team's findings were surprising. According to Bowie, the idea that bird songs rapidly evolve came from studying birds in the Northern Hemisphere, where environmental conditions have changed numerous times over tens of thousands of years. Northern Hemisphere birds may have evolved new colours, songs, and behaviours to better adapt to changing environments, such as the presence or absence of glaciers.

However, the East African mountains have seen very little geological change, implying that the sunbirds had no reason to evolve different plumage or songs. According to the statement and accompanying video, the researchers concluded that birds and their songs can remain unchanged for millions of years until environmental changes cause them to evolve quickly or in pulses.

"When humans are isolated, their dialects frequently change; after a while, you can tell where someone is from. And the song, too, has been interpreted in this manner "Bowie stated. "Our research shows that this is not always the case for birds. Even in traits that should be highly variable, such as song or plumage, long periods of stasis can occur."

Now, the scientists are continuing their research in East Africa to figure out why some birds evolve newer songs and others don't.