Things just got more complicated for crocodile watchers who must now look out for the sharp-toothed predators up trees as well in the water.

A study has found crocodiles across three continents are capable of climbing up tree trunks and then moving along the branches.

The unexpected skill is something for would-be Crocodile Dundees to bear in mind.

According to the journal Herpetology Notes, crocodiles leave land for the treetops when they need to bask in the sunshine to regulate their body temperature. They make the unlikely ascent when there is a lack of ground on which to catch enough rays.

But it seems the scaly creatures in the United States, Australia and Africa are bashful about being spotted up trees, with researchers reporting many crocs dropped in to the water whenever a human observer got within 10 metres of them.

Crocodiles are shy and cautious animals by nature, who happen to also have a mouthful of sharp teeth with bone-crunching strength. So perhaps the real reason the crocs took to the water was not to spare their own blushes but because lunch had shown up.

It is hoped the new study of tree-climbing crocodiles by zoologist Vladimir Dinets, of the University of Tennessee in the United States, could shed light on some aspects of croc evolution.

In the study the authors wrote: "Climbing a steep hill or steep branch is mechanically similar, assuming the branch is wide enough to walk on," the authors wrote. "Still, the ability to climb vertically is a measure of crocodiles' spectacular agility on land.

"The most frequent observations of tree-basking were in areas where there were few places to bask on the ground, implying that the individuals needed alternatives for regulating their body temperature," the authors wrote.

"Likewise, their wary nature suggests that climbing leads to improved site surveillance of potential threats and prey."