A million years ago, the soundtrack of the “sky island” mountains of East Africa may have been very similar to what it is today.
A million years ago, the soundtrack of the “sky island” mountains of East Africa may have been very similar to what it is today. That’s because a group of tiny, colorful birds has been singing the exact same tunes for more than 500,000 years — and maybe as long as 1 million years, according to a new study.
Sunbirds in the family Nectariniidae are colorful, tiny, nectar-feeding birds that resemble hummingbirds and are common throughout Africa and Asia. They are the “little jewels that appear before you,” senior author Rauri Bowie, a professor of integrative biology at the University of California, Berkeley, and a curator in the school’s Museum of Vertebrate Zoology, said in a statement.
The eastern double-collared sunbird (Cinnyris mediocris), also known as the “sky island sunbird,” lives at the peaks of tall mountains in East Africa from Mozambique to Kenya. These skyscraping peaks have isolated different populations, or lineages, of this species from one another for tens of thousands to a million years. But despite not interacting at all, many populations of sky island sunbirds are indistinguishable from each other.
Bowie and his team wondered if the birds’ songs had also remained unchanged through the eons. To answer this question, the researchers visited 15 separate sky islands in East Africa between 2007 and 2011, and recorded the songs from 123 individual birds from six different sunbird lineages. They then developed a statistical technique to analyze how the sunbirds’ songs evolved.
It turns out that, indeed, some of these isolated populations still sing the same songs. That suggests that these songs haven’t evolved much in the thousands of years that these lineages have been separated. The researchers also found, through analyzing genetic differences among the populations, that the two populations of species that had been separated the longest had nearly identical songs, whereas two other populations that were separated for a shorter time had very different songs, according to the statement.
The team’s findings were surprising, as biologists typically expect bird songs to evolve and change through time in different populations. The idea that bird songs rapidly evolve likely came from studying birds in the Northern Hemisphere, where environmental conditions have changed a number of times over tens of thousands of years, Bowie said. Northern Hemisphere birds are thought to have evolved new colors, songs and behaviors to better adapt to new environments, such as the presence or absence of glaciers.
But the mountains of East Africa have seen very little geological change, suggesting that the sunbirds had no reason to evolve different plumage or songs. The researchers concluded that birds, and their songs, can stay unchanged for millions of years, until environmental shifts cause them to evolve quickly or in pulses, according to the statement and accompanying video.
“If you isolate humans, their dialects quite often change; you can tell after a while where somebody comes from. And song has been interpreted in that same way,” Bowie said. “What our paper shows is that it’s not necessarily the case for birds. Even in traits that should be very labile, such as song or plumage, you can have long periods of stasis.”
Now, the scientists are continuing their research in East Africa to figure out why some birds evolve newer songs and others don’t.