Crows are intelligent birds: people in various parts of the world have noticed that crows of diverse species are adept strategists that use trickery and circumstance to get food (see Amazing Crow Stories). Crows are sometimes raised by humans and kept as pets, a role in which they interact with their human keepers in ways that are both amusing and exasperating—but which also suggest considerable intelligence on the part of the bird. People have taught crows to mimic human speech, and at least one species, Corvus moneduloides, the New Caledonian Crow, has demonstrated a surprising ability to fashion simple tools that make foraging for food easier.
Captive Crows Make Tools
In experiments with New Caledonian Crows in captivity, researchers at the University of Oxford have shown that the birds are able to selectively identify a stick that can be used to move food from an inaccessible location to a more accessible one. The crows also make hooks out of straight wire for the same purpose. When materials are available, New Caledonian Crows make hooks from barbed vines and probes from twigs and pieces of leaves. Equipped with these tools, the crows fish insects and grubs out of cracks and crevices, and probe in soft organic material. These activities have been observed in the wild but, because the crows move about so much while foraging, it is difficult to document their feeding and tool use activities.
Attaching Cameras to Crows
Until recently, the best documented evidence of crow tool use came from captive crows, but scientists have developed some new tools of their own: Christian Rutz, Lucas A. Bluff, Alex A. S. Weir, and Alex Kacelnik, researchers at the University of Oxford, UK, have attached tiny cameras to crow’s tail feathers and filmed the birds remotely, recording them selecting, making, and apparently saving tools for repeated use in the wild.
The minute cameras weigh about 15 grams and are attached, pointing forward, to the underside of tail feathers that are soon to be lost during moulting. The cameras broadcast video for about 70 minutes, beginning a couple of days after the device is attached to the bird, and also contain a locating device to track the movements of the wild crow and allow researchers to retrieve the camera after it has been shed. Cleverly, some of the cameras are sensitive to changes in posture and thus help to determine what the bird is doing.
Foraging and Tool Making in Wild New Caledonian Crows
The scientists were able to film the activities of 12 New Caledonian Crows in the wild. The birds foraged for food on the ground, a behavior that was not well known for this species until now, and in the trees: they built tools as they needed them, used them to probe and fish for food, and sometimes transported them to distant locations, suggesting that effective tools are sometimes kept for repeated use.
The study not only revealed new information about the feeding habits and tool use of New Caledonian Crows, it suggested that the use of small very light camera devices is a valuable way to get information about species that are difficult to observe in their natural habitats.
Related content:
How to Tell a Crow From a Raven
Sources:
“Crow Cams.” Behavioral Ecology Research Group
Firefly Encyclopedia of Birds. Perrins, Christopher ed. Buffalo: Firefly Books, 2003
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