The Story Of A Bird That Our Ancestors Thought Of As A Garden Companion, But Now Many Of Us Quite Simply Take For Granted!

The most widely distributed wild bird on the planet, they are found on every single continent except one, Antarctica.

The house sparrow is, perhaps, the bird species most associated with where humans live, both in rural, and urban areas. Although populations of the house sparrow have slowly declined across the world, sadly more rapidly in the UK, house sparrows are still an iconic part of many countries. The ‘chirp chirp’ every morning, deafening in some places, or the sight of a flock of birds in a bush, tree, or shrub is a beloved part of daily life in Britain and many other countries.

This makes it strange, that, until fairly recently, very little is known about this precocious little bird. It was thought the house sparrow may have originated in the Middle East, and then later spread across Europe and Asia. Later being introduced into Australia, New Zealand, and North America by European colonization. Eugene Scieffelin, the man who attempted to introduce all the birds in William Shakespeare’s sonnets and plays to North America late in the 19th century, may have been the man who introduced the sparrow to North America.

Mark Ravinet, an evolutionary biologist based at the University of Oslo, became interested in the origin of the house sparrow (Passer domesticus) when he realized the story of their evolution had not been properly assessed. In a paper, published in The Royal Society, he has shed more than a little light on the adaptation and evolutionary history of a bird many people take for granted. His research came up with two unforeseen though existing results.

It was shocking to see a very high level of difference between these commensal and wild lineages. That was the first indication that there was something quite striking going on here, said Mark Ravinet.

It was already clear that sparrows may have adapted to live alongside humans, because of their association with us over time. “If you look at a map of the distribution of the house sparrow, beyond its native range, it’s been introduced to North America, South Africa, Australia. It doesn’t take long to join the dots and realize the people who introduced it were Victorians in the expansion of the British Empire,” said Ravinet. The British thought of the sparrow as a kind of ‘garden companion’, he says, which would make them feel at home while abroad.

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It had been thought the species diverged with the spread of agriculture over time, and Ravinet’s team formally tested this theory for the very first time. “I wouldn’t go as far as to say that my paper definitively proves it, but certainly it strongly suggests that that is the case, that they have spread with agriculture,” said Ravinet.

The next task was to compare the DNA of the house sparrow with the Bactrianus sparrow, a wild subspecies of the house sparrow.

“When I visualized it, I expected them to be really similar, I thought there would be some differences but relatively minor,” said Ravinet. “It was shocking to see a very high level of difference between these commensal and wild lineages. That was the first indication that there was something quite striking going on here. That led us down this pathway of starting to investigate in a bit more detail what possibly could have happened to drive this.”

One cold, dark evening Ravinet sat in his office and started the analysis. He found two genes that were different.

“I Googled the first one and realized it was involved in skull morphology and that got me really excited,” he said. “As soon as I saw the other one I recognized it because it’s involved in dogs and humans. I checked a closely related species and those genes are very far apart. It suggested that something special might have happened in the house sparrow.”

He double-checked, and checked again in the morning, before telling his colleagues what he had discovered. The two genes he found were COL11A—which regulates craniofacial and skull development – and AMY2A, part of the amylase gene family which has previously been linked to adaptation to high-starch diets in humans and dogs.

A robust thicker skull may have something to do with a transition in diet towards agricultural-based grains. “We know skull shape is likely to be an important adaptation to feeding on human resources,” he said.

“Most sparrows feed on insects when they’re nursing their young. House sparrows tend to feed on grain throughout the year when they’re not breeding. It’s hard to get an idea what wild sparrows might have lived like, but probably on wild seeds, grasslands.”

These results are only the beginning of a much bigger project. Ravinet and his team are currently following up on findings. One student is CT-scanning about 100 skulls to identify differences in morphology. Ravinet will also be sequencing the genomes of all the different species of sparrows.

Still, this early research makes you think differently about the common, very familiar sparrow outside your window, and how our evolutionary histories are intimately intertwined.

For more details please go to bbcearth.com.

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