New Caledonian crows are known for their ability to craft plant branches into crochet-like hooks to help them snag insects, but experience may make them lazy, researchers said Thursday.

The wisest and oldest crows tend to take shortcuts, employing a quick and dirty method rather than the most careful beak-driven approach employed by younger crows.

According to the study in the journal Current Biology, juvenile crows tended to make controlled cuts to plants and sticks using their bills, resulting in much deeper hooks.

Older birds often used the sloppier method of simply pulling off branches, leading to shallower hooks.

"I suspect that there are costs associated with making tools that have really deep hooks, and that experienced adults may be avoiding these costs," lead author Christian Rutz, a biology professor at the University of St. Andrews, told AFP.

"This could include the extra time and effort that may be required for making deep hooks."

Even though deep hooks tended to help crows get insects out of holes faster, they might not be best in all foraging contexts.

"For example, they may break more easily if they are being inserted into very tight holes or narrow crevices," Rutz explained.

Scientists have marveled for years at the unusual ability of these specific crows -- native to France's South Pacific territory of New Caledonia -- when it comes to tool-making.

Although dolphins, elephants, chimpanzees and other birds have been found to use tools, making hooks is a realm of its own.

"From all we know it's only New Caledonian crows and humans that craft hooked tools in the wild," said Rutz.

"Hook innovation marks a major transition in human technological evolution, so these crows offer fantastic opportunities to examine how such tool designs may arise, and how technologies may gradually advance further."