Last updated at 13:32
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Pictures: Fake caterpillars help scientists to trick birds

Canadian scientists are using replica caterpillars made from dough to find out how their "eyespot" camouflage works.
"Now that we have shown that eyespots can protect caterpillars, we are looking to understand why some species evolve eyespots and not others," said Mr Hossie, whose study is published in the Animal Behaviour journal.
Measuring the butterfly of Papilio canadensis
This one's real too. It looks like a snake, with its green colouring, striking eyespots and a bright orange 'tongue' called an "osmeterium". It's not actually a tongue, and on caterpillars the eyespots aren't real eyes either! That's one reason why the scientists are studying them - to work out what the markings are there for.
Papilio canadensis on a leaf
They found that the models without eyespots were pecked at both ends, but those with eyespots were attacked less at the spotted end. This suggests that the markings do indeed intimidate some birds.
Caterpillar model with peck marks at head and tail
Although over half the models were destroyed or taken by predators, some survived better than others. If they had just shading, or just eyespots, the fakes ended up still being attacked. But the trick-caterpillars with both features were attacked far less often.
Caterpillar model destroyed
And now to the fakes! Thomas Hossie from Carleton University, Ottawa, made 864 model caterpillars, using dough and food colouring. He tested models with and without eyespots and changed their shading to see which ones the birds attacked.
Caterpillar models made using modelling clay
Thomas put the caterpillars in real life situations, like trees, to see if their eyespots put off predators. They hoped that the bigger the eye, the less likely they would be pecked at by birds.
Caterpillar model with ants
Canadian scientists are investigating whether eye patterns on caterpillars' heads stop them from being attacked. The plan is to find out if the eye spots and markings on the top can scare off predators like birds. This one's a real caterpillar!
Canadian tiger caterpillar (Papilio canadensis) on a leaf