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.
Researchers at the University of California Berkeley concluded that this is how isolated populations of sunbirds with double collars were found in high-altitude 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.
The team clarified that this truth was derived primarily from observations of Northern Hemisphere birds.
This species has been subject to extreme environmental changes over many thousands of years. Glaciers have come and gone repeatedly.
These changes have facilitated many evolutionary improvements, including the alteration of bird song and plumage as well as mating behavior.
However, the bird communities living in isolated areas on East African mountain peaks such as Mount Kenya or Mount Kilimanjaro have experienced more stable 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.
The sunbirds did not say that their tunes were changing gradually over time. They suggested instead that they experience long periods of static punctuated with rapid pulses 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.
Scroll down to see the video
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. The researchers studied a double-collared Sunbird, Cinnyris.
The research was undertaken by integrative biologist Rauri Bowie of the University of California, Berkeley and his colleagues.
“If you isolate people, you will notice that their dialects change quite often. After a while you’ll be able to tell where someone is 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 when traits should be very flexible [liable to change]You can experience long periods of stasis with certain activities, like song and plumage.
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.
This discovery led Professor Bowie to question if birds could have been just as consistent in singing their songs as they were with 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 sunbird lineages. Pictured: the ranges of the lineages across Kenya, Malawi, Mozambique and Tanzania
Researchers discovered that differences in songs of sky islands sunbirds did not correlate with how long each population was separated, as indicated by their DNA profiles.
One example: Two of the species separated for so long had almost identical songs. However, two species isolated from one another for much longer presented wildly differing tunes.
Jay McEntee, paper writer, said that what surprised him most about this research was how similar the learned songs were within species and the apparent song differences in places they occur.
“The first time” [fellow researcher] Maneno Mbilinyi and I were making a sound recording of Cinnyris fuelleborni — what we call Fuelleborn’s sunbird — we thought there must be a different bird nearby that was singing simultaneously.
‘The song we were listening to didn’t make sense to us.
The singing bird is directly in front of you. Watch it use its beak to move. [we] couldn’t believe just how different its song was from the really similar-looking Moreau’s sunbird which we had just been recording in a different part of the Udzungwa Mountains.’
In contrast, the biologist noted, the songs of the C. fuelleborni populations in Ikokoto, Tanzania and Namuli, Mozambique are almost identical — despite such have been separated for hundreds of thousands of years.
According to the researchers, the song differences of the sky island sunbirds were not related to the time each one had existed apart from others. This was based on the DNA differences between the populations. Left: The six lineages with the typical plumage and center sonograms showing their representative songs.
The team concluded that plumage, learned song, and other characteristics don’t inherently wander in isolated birds populations. They instead likely evolve in rapid pulses that are punctuated by long periods of consistent behavior.
Professor Bowie stated, “We’re showing that song evolution can be studied using isolated natural populations in a very nice setting. This shows you don’t notice this gradual change due to cultural or genetic drift.”
These sudden changes in birdsongs and other traits can be seen as evidence for stability. This is a very unusual trait that should never change.
He said, “This was to me, an absolutely fascinating result,” he added.
With their initial study complete, the team are now continuing their work in East Africa with the goal of determining what drives some birds to change their tunes while other species are content to sign the same song for thousands of years.
All findings of the study have been published in the Proceedings of the Royal Society, B: Biological Sciences.
Jay McEntee, paper author said that what surprised him most about this study was how similar the learned songs were within isolated species. And how evident the differences in song are where they occur. Jay McEntee said, “This is the first time that I have done this.” [fellow researcher] Maneno Mbilinyi and I were making a sound recording of Cinnyris fuelleborni — what we call Fuelleborn’s sunbird — we thought there must be a different bird nearby that was singing simultaneously.’ C. fuelleborni artist impression