Why do hummingbirds have such a sweet tooth?

Unlike any other birds, hummingbirds seek out sugary nectar. It’s allowed them to successfully fill a very specific niche in the animal world.

But how come they’ve developed a taste for the sweet stuff? Well, scientists have recently discovered it’s all in the genes.

So, what have they found out?

(Larry Steagall/AP)

Scientists analysed the genetic codes of 10 bird species and found that hummingbirds were the only one that had a genetic adaptation making them drawn to sweetness.

A taste receptor normally geared up for savoury (known as “umami”) flavours which come from amino acids had been altered to instead respond to sugary carbohydrates.

At least 19 genetic mutations – possibly more – were involved in this transformation from savoury to sweet.

What’s the scientific background to all this?

(Brennan Linsley/AP)

Experts split up taste receptors into five broad categories: salty, sour, bitter, sweet and umami – from the Japanese word for savoury.

Before scientists had sequenced the chicken genome (all the genetic code of that animal) it had always been assumed that birds and mammals shared exactly the same taste receptors.

But scientists could find no trace of a sweet receptor gene in either the chicken or many other bird species. Which lead to the question: why do hummingbirds hover around flowers in search of sweet nectar?

What did the experiments involve?

(Barry Batchelor/PA)

The hummingbirds showed themselves very sensitive to sweet tastes.

Shaking their heads, they spat out tasteless water. They were also not fooled by the sugar substitute aspartame that we use to flavour “sugar free” drinks.

But they lapped up an artificial sweetener that laboratory tests had already predicted they would find irresistible.

Why are the experts excited?

(Michael Sullivan/AP)

Dr Stephen Liberles, from Harvard Medical School, explained how the team’s research showed a great example of how animals evolve at the molecular level.

“If you look at the (molecular) structure of the (taste) receptor, it involved really dramatic changes over its entire surface to accomplish this complex feat,” he said.

“Amino acids and sugars look very different structurally, so in order to recognise them and sense them in the environment, you need a completely different lock and key. The key looks very different, so you have to change the lock almost entirely.”