Crows fashion hooks out of wood to get food
Crows are probably one of the most recognizable birds in North America, especially considering their distinguishable loud, piercing calls.
Crows are scavengers and predators, but they are also highly intelligent and able to problem solve and even craft tools to get food in hard to reach places.
Biologists from the University of St. Andrews set out to examine how the New Caledonian crow fashions its most sophisticated tool, a stick with a hook at the tip.
The study was published in the journal Current Biology and further emphasizes the intelligence of New Caledonian crows, which are the only animals that make hooked tools in the wild.
Other species have been observed using sticks and rocks to aid them in getting food, but the Caledonian crow is the only crow that purposefully fashions the end of a stick into a hook-like shape.
Christian Rutz, the leader of the study and an expert on Caledonian crows, noticed that the hooks the crows were making varied greatly in size and shape.
This led the researchers to wonder why there was such inconsistency in how the hooks were made, and if certain shapes or styles of hooks had an advantage for getting food.
“We suspected that tools with pronounced hooks are more efficient, and were able to confirm this in controlled experiments with wild-caught crows,” said Rutz. “The deeper the hook, the faster birds wrinkled bait from holes in wooden logs.”
When it comes to making tools, there are two important factors to consider: the quality of the materials and skillset.
The more intricate hook depended on the crow that was making the tool and the kind of wood or plant material that was being used.
If the crow employed controlled skillful “cuts” with their bills, the hooks were deeper than if the crow just pulled away branches.
Even though careful cutting and shaping of the sticks leads to better hooks, the researchers found that adult Caledonia crows more often than not just stripped away branches and didn’t take time to fashion or carve the hooks.
This means that deeper hooks are not particularly advantageous in the wild.
“It probably takes more time and effort to make such tools, and experienced birds may try to avoid these costs,” said Rutz. “It is also possible that deep hooks break more easily when inserted into narrow holes and crevices.”
The study shows what goes into tool making for New Caledonian crows, and could also help paleo-anthropologists understand the evolution of tool making in humans.