Talk about having a tune stuck in your head — some East African sunbirds may have been singing the same song, passed down the generations, for up to a million years.
This is the conclusion of University of California, Berkeley-led researchers who studied isolated populations of double-collared sunbirds living up high mountains.
Bird song is traditionally thought to change easily thanks to how it is passed down by mimicry and, like in a game of 'telephone', is susceptible to distortion.
However, the team explained, this truism has been derived principally from studies of birds that reside in the Northern Hemisphere.
These species have seen highly changeable environmental conditions over the last few tens of thousands of years, with glaciers coming and going repeatedly.
This has fostered various evolutionary changes, affecting not only bird song but also their plumage and even mating behaviours.
The bird populations living isolated lives up forested East African peaks like those of Mount Kenya and Mount Kilimanjaro, however, have enjoyed more static conditions.
And the team found that — despite these habitats having been separated for tens of thousands or even millions of years — their birds still sung very similar songs.
Rather than the sunbirds' tunes changing slowly over time, they said, it appears that such undergo long periods of stasis punctuation by rapid pulses of change.
Among the most diverse and colourful groups birds in Africa and Asia, sunbirds occupy a similar niche to that of the America's hummingbirds — sipping nectar.
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Talk about having a tune stuck in your head — some East African sunbirds may have been singing the same song, passed down the generations, for up to a million years. Pictured: a double-collared sunbird from the genus, Cinnyris, studied by the researchers
The research was undertaken by integrative biologist Rauri Bowie of the University of California, Berkeley and his colleagues.
'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,' explained Professor Bowie.
'What our paper shows is that it’s not necessarily the case for birds.
'Even in traits that should be very labile [liable to change], such as song or plumage, you can have long periods of stasis.'
Professor Bowie said that he has long been fascinated by sunbirds — and in particular those species, which having become isolated on the top of high mountains, are commonly known as 'sky island sunbirds'.
In a previous study, the biologist showed that what had long been thought to be just two species of eastern double-collared sunbirds that live over several mountaintops in East Africa actually represent five, or even six, individual species.
These birds — despite still looking alike — exhibit significant genetic differences thanks to having evolved in isolation over long periods of time.
The finding led Professor Bowie to wonder if the birds might have been as unchanging in the songs that they sing as they were in their plumage.
To find out, the researchers visited 15 East African 'sky island' mountaintops between 2007–2011 and recorded the songs of 123 individual birds for each of the six different eastern double-collared sunbird lineages.
The researchers visited 15 East African 'sky island' mountaintops between 2007–2011 and recorded the songs of 123 individual birds for each of the six eastern double-collared
