December 13, 2001
Crafty crows flock to thievery
Crows and ravens are depicted as being clever and tricky animals in countless American Indian stories and legends. Those characterizations apparently are right on the mark, according to a pair of UW researchers who have found a species of crow that is constantly looking for opportunities to steal food from other members of its flock.
In fact, the behavior is so prevalent among Northwestern crows (Corvus caurinus) that it shatters the long-held belief of some animal behaviorists that the birds primarily are looking for predators when they scan their surroundings, report Renee Robinette Ha, a UW lecturer in psychology, and James Ha, a research associate professor of psychology.
Their findings were recently published in the journal Animal Behaviour.
“Crows and other corvids (ravens, jays and magpies) are highly intelligent,” said Renee Ha. “Among birds, only parrots match them in intelligence. Crows are social, highly cognitive birds whose intelligence is up there with dogs.”
“Crow vigilance is based on the opportunity to steal food,” said James Ha. “The over-riding factor in their vigilance behavior is ‘Who’s got food I can steal?’ not ‘Is there a predator lurking around?’ It has been dogma that crows are vigilant for predators, but they really are vigilant about each other.”
To observe crows, the Has needed an open, non-wooded site where the birds’ behavior could be readily seen. They found it in Meadowdale Park, a suburban site along Puget Sound in Snohomish County, north of Seattle. The park is relatively undeveloped with light human and dog traffic, which might have disturbed the birds.
The researchers observed crows for 290 hours over 18 months, watching a randomly selected bird for five minutes. All observed birds, which were in groups ranging between five and 50 individuals, were within one meter of the exposed tidal zone where food was available. The birds were observed through binoculars from a distance of 30 to 50 meters.
Among the available prey were sand lances, silvery fish the size of sardines that burrow into the sand. Other food sources include invertebrates such as clams, worms, shore crabs and snails. Larger prey such as sand lances, clams and crabs cannot be quickly consumed, and crows that catch them often become the targets of their thieving neighbors.
“Finding that chance to steal food is a very uniform strategy among these birds,” said Renee Ha. “They are not like the crows in the city that forage for food in dumpsters.”
As for predators, the researchers witnessed several bald eagle attacks while they were observing the crows. The researchers previously documented some eagle predation on crows, but they did not observe a bald eagle killing a crow during this study. Typically, when an eagle flew over the beach, the crows flew up and mobbed the eagle until it left the area.
“If you have a varied environment like a forest, crows can only be intermittently observed,” said James Ha. “But on an open beach we have a stable system to study, and we’ve been able to open a door on crow behavior because we can see what they are doing all the time, what they are feeding on and how they are using their cognitive behavior in the wild. We also can band birds and watch them year after year.”
The Has are continuing their research, using DNA to focus on what they describe as a “very complex family system” to further understand the crows’ behavior.
The Animal Behavior Society; Sigma XI, a scientific honor society; and the UW Graduate School funded the vigilance study.