Crows can hold grudges for up to 17 years

Studies and experiments worldwide have repeatedly shown that crows excel at memory, intelligence and self-awareness, displaying cognitive skills that challenge conventional assumptions.

Although birds are commonly appreciated for vivid plumage and melodious songs, a less visible dimension of their behaviour deserves attention.

Birds are more intelligent than many people assume, particularly in their ability to remember individuals they regard as threatening.

Recent research has brought this striking aspect of avian behaviour into focus: crows – among the most accomplished birds – can retain grudges for as long as 17 years.

The finding demonstrates the remarkable depth of crows’ memories, while also revealing how knowledge about threats can spread socially through bird communities.

Studying crows and grudges

Experts at the University of Washington began this research project in 2006.

Professor John Marzluff, an environmental scientist, started the experiment by putting on a frightening mask and briefly catching seven crows. Before safely releasing them, he fitted the birds with leg rings for identification.

Over the following years, Marzluff and his assistants occasionally wore the same mask while walking around the university campus and feeding the crows living there.

Marzluff remembered one masked outing during which 47 of the 53 crows he came across loudly scolded him.

That figure was far greater than the seven crows initially caught, indicating that these birds could identify humans perceived as dangerous and communicate that knowledge to relatives.

The sound of silence

The study reached its high point in 2013, when aggressive calling was at its most frequent before beginning a gradual decline.

In September 2023 – 17 years after the experiment started – Marzluff heard no scolding crows at all during one of his walks in the mask.

Seeing behind the mask

A further compelling part of the research used a “neutral” mask depicting Dick Cheney, who was serving as vice-president of the United States at the time.

People wearing the Cheney mask fed the crows without causing distress, and consequently did not face the birds’ anger.

As the work continued, volunteers who did not know whether the crows considered a mask “dangerous” or “neutral” were recruited to wear them.

One volunteer became the focus of a noisy avian commotion, supporting the evidence that crows can distinguish threats and remember them.

Dive-bombing attacks by crows

A report in Mail Online describes further examples of grudge-holding crows. Residents of Dulwich, an affluent London suburb, reported crows carrying out dive-bombing attacks.

One resident, Alison Frean, recounted a frightening experience, saying crows had targeted her on three separate occasions as she tried to get out of her car.

The incidents affected local people so strongly that they stayed indoors in an effort to avoid encounters with crows.

Crows, memory, and grudges

Crows continue to impress with exceptional intelligence that extends well beyond recognising threats and keeping grudges.

Earlier research suggests that crows can create tools and even count.

There are many accounts of crows placing nuts on busy roads, waiting for passing vehicles to crack them, then collecting the food after traffic has stopped.

Certain crows have also learnt to use sticks to remove insects from bark, or to make hooks from twigs for reaching food in inaccessible places.

The University of Washington study clearly strengthens the case for crows’ high standing in the avian intelligence hierarchy.

Crows seem to be animals with long memories, retaining grudges and recalling dangers even across a period of 17 years.

Social dynamics of crow behavior

Alongside their impressive memory and intelligence, crows display intricate social arrangements that further underline their cognitive sophistication.

They live in close family groups and show behaviour that points to complex emotional lives.

For example, crows have been seen holding what seem to be “funerals” for dead members of their flock.

Their communication is highly developed, incorporating varied vocalisations and even regional dialects.

This communication involves more than alerts about possible dangers: crows have also been observed exchanging information about food and forming alliances to repel predators.

Animals and cultural transmission

Among the most notable elements of crow behaviour is their capacity to teach each other.

If one crow learns that a particular person or object represents danger, it can communicate that information to other members of its community, quickly spreading awareness.

Learning within the group helps maintain and pass on knowledge of possible threats, enabling young crows to identify dangers without experiencing them directly.

This sophisticated web of social interaction places crows among the small number of non-human animals able to engage in cultural transmission – transferring knowledge between generations.

It is therefore unsurprising that many cultures revere these birds and frequently regard them as emblems of intelligence and adaptability.

The complete study was published in Proceedings of the Royal Society B.

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