Crows are the only birds that have learned to carve hooks from sticks and hunt for food

Crows have the mental capacity to craft hooks out of sticks and use them as tools to fish out food, find researchers in the University of St Andrews (UA). Apart from Caledonian crows, only humans have demonstrated this ability.

The crows were found to be able to fashion sticks from the side branches of certain plants and make crochet-like hooks that they then used to fish out insects from between branches and other hard-to-reach spots.

Even humans who have been hunting and making tools for about three million years did not make tools till about 23,000 years ago, according to Science Daily which cites the study. It turns out hooks are quite advanced and not that easy to simply dream up.

Professor Christian Rutz, from the School of Biology at UA, has been studying New Caledonian crows for over a decade now. Last year, a report on how the crows were found to be skilled at making tools out of straight sticks was released.

The same team has now found the crows to be adept at making hooks as well - more than one type of hook. Some of them are barely curved and look more like a protrusion at the tip. Others are properly curved and neatly bent.

"We suspected that tools with pronounced hooks are more efficient, and were able to confirm this in controlled experiments with wild-caught crows. The deeper the hook, the faster birds winkled bait from holes in wooden logs," said Rutz.

When making hooks, crows seem to employ methods that are similar to the way humans work. This means making sure that both the material and the method used to fashion out a tool are of equal importance.

Crows also used a similar approach. The researchers found that the depth of a hook made by a crow is determined by how good the raw material is and how experienced the crow is at making tools. Crows that used their sharp bills to make precise cuts along the wood to shape it accurately were able to make deeper, more pronounced bends. Some crows even left a bit of material at the end of the stick to make a better bend and then sculpt the piece of wood perfectly.

Another method used by older crows which did not really want to go through with the sculpting process was to simply cut off surrounding branches and pull out curved sticks. These hooks did not have deep hooks, rather, sloped ones. "It probably takes more time and effort to make such tools, and experienced birds may try to avoid these costs. It is also possible that deep hooks break more easily when inserted into narrow holes and crevices," said Rutz.

Even chimpanzees, known to be among the smartest animals, do not craft hooks, notes the report. They simply make use of curved sticks as tools.

Crows have sharp bills like pliers that can snip out twigs and shape them. Chimps, with their large fingers would not be able to carry out this task, notes Christophe Boesch, a world-leading chimpanzee expert.