Unforgiven: Crows can hold grudges for 17 years

The birds can harbour a grudge for as long as 17 years against those who upset or threaten them, a scientist has found.

A scientist in America has conducted an experiment that suggests crows can remember the faces of people who have been mean to them, and also pass on the grudge to other crows

Are you the type who quickly forgives and forgets? Or do you still carry a burning anger over small things that happened decades ago? If it is the latter, you may have something in common with crows.

The birds can harbour a grudge for as long as 17 years against those who upset or threaten them, a scientist has found.

If you ever find yourself dive-bombed or aggressively cawed at by a crow, you must ask yourself: did you do anything to upset that particular bird – or any of its friends or relatives – over the past two decades?

Crows are either unable or unwilling to forgive threatening behaviour, researchers have said. Instead, they use their renowned intelligence, including an alarmingly good memory for faces, to pursue and harangue their abusers, in some cases for several years. It has led the residents of some cities to start logging attacks from angry crows.

Scientists have now discovered just how long a crow’s grudge can last. Alexander Pope once wrote that to forgive is divine, but it may be more apt to ­misquote William Congreve and warn that hell has no fury like a crow scorned.

John Marzluff, an environmental scientist at the University of Washington, discovered this after subjecting a murder of crows to an unpleasant incident in 2006.

He put on an ogre mask and captured seven crows in a net, attaching identification bands to the birds. He soon set them free unharmed, but the episode was traumatic for those crows and others who witnessed the incident, Professor Marzluff told The New York Times.

Over the following years, Professor Marzluff and his assistants would occasionally put on the ogre mask and walk around the campus, monitoring if the resident crows let out aggressive “scolding” caws in their direction.

On one occasion he was scolded by 47 of 53 crows he encountered. This was far more than the number that experienced or witnessed the initial incident, suggesting that crows learn to recognise threatening humans from their parents, relatives and murder-mates. This is likely to explain how the murder of crows, whose individual members live for less than a decade on average, was able to bear a grudge for so many years, passing on their anger down the generations.

The number of angry caws grew to a peak after seven years. From 2013 onwards, the number of aggressive caws started to fall until, during one walk in September last year no scolding calls were logged for the first time since the start of the experiment, 17 years after it began. He is preparing to publish the data from his study.

At the start of the experiment, researchers also used a “neutral” mask: the face of Dick Cheney, then US vice-president. Those wearing the Cheney mask fed the crows without subjecting them to any trauma. Researchers who wore the Cheney mask later were not abused by angry crows.

In another part of the experiment, students used another set of masks while trapping crows around Seattle. Volunteers were then asked to wear the masks without knowing which were deemed “dangerous” or “neutral” by the crows.

One volunteer who donned a “dangerous” mask, Bill Pochmerski, told The New York Times: “The birds were really raucous, screaming persistently, and it was clear they weren’t upset about something in general. They were upset with me.”

The Times