The results of Hunt's study are published in the December 13 issue of the journal Nature.
Food "Cost-Benefit Analysis"
In another study of crows, researchers have found that Northwestern crows (Corvus caurinus) in the United States constantly scan their surroundings for opportunities to steal food from other birds.
Most animals and birds, when in groups, tend to be less vigilant and spend more time eating. That is not the case with Northwestern crows.
Animal behavior specialists have long thought that the crows, when they scan their surroundings, are on the lookout for predators. But the new study reveals that the birds are shrewdly watching other crows for opportunities to steal food.
Renee Robinette Ha and James Ha, both of the University of Washington in Seattle, have found that Northwestern crows perform a "cost-benefit analysis" before deciding what food to steal from another member of the flock.
"They don't steal just any type of food," said Robinette Ha. "They only steal food that requires a long handling time, like crabs or clams, or foods that are high in energy."
Crabs and clams require time and energy to break open and access the meat. Crows drop clams on rocks to smash them open. This attracts the attention of other birds, which hover waiting to snatch a free morsel.
Sand lances, silvery fish the size of sardines that burrow into sand at low tide, are another popular target of marauding crows, said Robinette Ha.
Sand lances are difficult to find. Researchers are not sure whether the crows can hear them or feel vibrations as the fish burrow. But once a crow begins to dig, other crows form a circle around the digger, waiting in ambush. As soon as the fish is pulled out of the sand, the other crows try to snatch it away.
The crows don't attempt to steal fast food such as bugs and worms.
"These birds are tremendously clever," said Robinette Ha. "They are adapable and have complex social life and interactions, which makes them challenging to study."
This study was published in a recent issue of the journal Animal Behaviour.
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