New research by an international group of scientists, including some in Ireland, has discovered the Hummingbird has developed a sweet tooth that makes it different from all other birds.

The scientists found the difference came about as a result of a genetic adaptation, which transformed their savoury taste receptor into a sweet one.

Birds descended from therapod dinosaurs, and because dinosaurs lost the ability to taste sweetness, birds were also left without a sweet tooth.

Yet, Hummingbirds have somehow managed to evolve the ability to taste sweet things.

This has led them to thrive, because as result of their adaption they are able to exploit a food source that other birds do not know about - nectar.

In an effort to try to explain why that is the researchers, including Dr Mary O'Connell of the Bioinformatics and Molecular Evolution Group at DCU and her team, sequenced the genome of ten bird species.

They found that the Hummingbird has evolved up to 19 genetic mutations, which has enabled it to use a transformed umami taste receptor for tasting sweetness instead.

umami is the savoury flavour - like that found in cured meats and aged cheeses.

In a paper in the journal Science, the scientists describe how they made part chicken and part Hummingbird proteins in the lab.

By doing this they were able to work out which parts of the protein react to sugar, and which don't.

They then combined this work with behavioural studies of how Hummingbirds react to different substances, like sugar, artificial sweeteners and water.

They found the birds were acutely sensitive to sweet tastes.

Shaking their heads, they spat out tasteless water and were not fooled by the sugar substitute aspartame that flavours sugar free drinks.

But they lapped up an artificial sweetener that laboratory tests suggested they would find irresistible.

Lead scientist Dr Stephen Liberles, from Harvard Medical School in the US, said: "It's a really nice example of how a species evolved at a molecular level to adopt a very complex phenotype.

"If you look at the structure of the receptor, it involved really dramatic changes over its entire surface to accomplish this complex feat.

"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."