Above the Clouds in East Africa: Mr. Bowie and the Old Songs - Knowledge

In East Africa, the wooded peaks of the highest mountains are called sky islands. Anyone who climbs one often sees other peaks like islets, sky islands, rising out of the sea of clouds. Animals well-adapted to these habitats high above true and cloud sea level are correspondingly well insulated from conspecifics on other islands of the sky.

According to the theory postulated by Charles Darwin and further developed by the German evolutionary biologist Ernst Mayr, ideal conditions should prevail here for the development of new characteristics and the emergence of new species.

Like the hummingbirds

But that is only partly true. This was recently discovered by a team led by bird song expert Raurie Bowie from the University of California at Berkeley. The researchers studied sunbirds living in these isolated habitats.

singers in the east. The six lineages Cinnyris mediocris are found isolated on mountains (black) throughout East Africa. Many of the…Photo: UC Berkeley

The animals closely resemble those native to America hummingbirds. They have long, often heavily curved, beaks to reach the sugar-rich liquid of various flowers. And they flap their wings at high frequency.

Hummingbirds and sunbirds are an example of “convergent” evolution: comparable adaptation to comparable environmental conditions and thus often similar appearance and behavior. An example of divergent evolution, however, as one would expect from isolated populations, is not among sunbirds.

Always the old song

It is true that they have developed so differently genetically over millions of years that they are classified as different species. But the songs of the males are almost identical in many cases. This is how Jay McEntee from Missouri State University, Bowie and ten other researchers recently reported in the “Proceedings of the Royal Society B“.

song keeper. Upland sunbirds are conservative.Photo: N. Voaden; Wikimedia Commons

This applies to distant populations of a species as well as to different species. It probably means that some of the chants were being sung in exactly this way as long as 500,000 or a million years ago. The researchers attribute this stability to the stability of the habitats. So far, however, it was assumed that this should hardly affect characteristics that have nothing to do with direct interaction with the habitat – for example, competitors for food or flowers.

Sonograms (right) of representative calls of the six lineages of the sunbird species Cinnyris mediocris. These lines are (left)…Photo: UC Berkeley

Features like Song or plumage pattern should actually change significantly over time. But even in terms of plumage, some species there are so similar that they have long been grouped into a single species. Evolution, the study authors conclude, did not happen continuously in these species and in those cases where the songs differ significantly today, but in leaps (“punctuated evolution”) – and probably with environmental changes as a trigger.

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