This Crow’s Beak Evolved to Wield Tools

Sometimes we adapt tools to suit our purposes. Sometimes nature adapts us to suit our tools. For example: ornithologists say the bills of some crows have evolved to help them hold and manipulate their tools. The researchers published their findings in the journal Scientific Reports.

Scientists are beginning to realize that birds are much sharper than we previously realized, but even by bird-smarts standards, the New Caledonian crow (Corvus moneduloides, also known as the NCC) is special. The NCC’s ingenuity is exclusively food-driven, although their foods of choice are bugs and grubs that live in tree trunks. To extract their prey, NCCs make fishing rods and hooks by trimming excess pieces from slender sticks and barbed leaves. There’s only one other animal on Earth that makes fishing hooks: humans.

Scientists say these sophisticated behaviors are made possible by two of the crow's features: its brain and its beak. The latter's uniqueness is a new discovery, but the epiphany that inspired it is nearly 20 years old.

Ornithologist Kevin McGowan was looking at stuffed bird specimens one day in the late '90s when he noticed the NCCs. "I remember saying to a student, 'I don't know what this bird does, but it does something different from any other corvid on Earth because its bill is so weird,'" McGowan recalled in a press statement.

A few years later, in 2000, a researcher named Gavin Hunt published a paper on the NCC’s extraordinary tool use. As McGowan read the paper, a light bulb went on in his head.

Then, McGowan, Hunt, and seven of their colleagues in New Zealand and Japan decided to find out if their suspicions were right. They used computed tomography, better known as CT scanning, to make 3D images of the beaks of 11 species: NCCs, nine of their relatives, and black woodpeckers, which feed on the same in-tree grubs and bugs as the NCCs. The researchers created 11 reference points, or landmarks, so they could compare the beaks’ proportions and dimensions.

Image Credit: Matsui et al. 2016

The researchers found that McGowan was right—the shape of the NCC’s beak is completely unique. "Their bill is shorter than a regular crow's," McGowan said. "It's blunter, and it doesn't curve down like nearly all bird bills do.”

There’s a reason for that. NCCs hold their tools in their beaks, and they have perfected a technique that requires holding the stick or leaf at a specific angle. Over generations, the NCC’s beaks have obligingly curved to make this possible.

“The lower mandible actually curves slightly up, which likely gives it the strength it needs to hold the tool," McGowan said. "And because the bill doesn't curve downward it brings the tool into the narrow range of the bird's binocular vision so it can better see what it is doing."

Just like a left- or right-handed human holding a tool, each crow has a dominant side. "They hold the stick tool so that it goes up along the side of their head along the length of the bill," McGowan said. "Apparently there are birds that favor one side of the head over the other—left-sticked or right-sticked, you could call it—it’s really cool."