Previous research has found crows have an excellent memory for human faces.
Crows mourn their dead to try and learn about potential dangers to their own lives, researchers have found.

They found the birds can even remember an animal or person seen with a dead crow.

The birds were also able to easily distinguish between people or hawks carrying dead crows and other birds.

'The funeral behaviour of crows is so widely observed, and people often asked about it - but we haven't known what was happening,' Kaeli Swift at the University of Washington, who led the research, told

The study recorded the crow's behaviour when stuffed crows which appeared dead were introduced to areas where they are feeding.

'I introduced one of my three dangerous scenarios: a masked person holding a dead crow, a masked person standing near perched hawk, and a masked person standing near a perched hawk with a dead crow.'

In all these cases the birds were taxidermy-prepared mounts.

'The masks were used to work out how the crows recognised people - I had different volunteers each week,' Swift said.

In 96% of cases , the response was the same.

'The discovering bird (usually the territory holder) would scold and typically attract 5-11 additional birds.

'The mob would stick around for 10-20 minutes, scolding loudly and gradually growing more silent and dispersing before all but the territory holders were left.'

Exposure to the dangerous stimuli would only last 30min, after which they were removed.

Volunteers wore realistic facemasks with neutral expressions for the experiments so the crows could recognise faces even though different volunteers were underneath them.
'I found that crows responded most strongly when they saw a person and a hawk with a dead crow as opposed to a person holding a dead crow or a person near a hawk,' said Swift.

'This tells us that context matters, and crows are most sensitive to dead crows when they're with familiar predators.

Even after 6 week, 38% of the 65 pairs eligible for all 6 tests continued to respond to the 'dangerous' person.

Previous research has found crows have an excellent memory for human faces, and Swift said the team have a pending publication on exactly how long they remember for, and said it is 'years'

She admits she was surprised by some of the results - in particular the fact crows learnt to recognise people simply standing near hawks.

'That was really surprising.'

Dr John Marzluff, of the University of Washington, has carried out previous studies in the area.

'Our findings add to the evolving view of large-brained, social and long-lived birds like crows being on a cognitive par with our closest relatives,' he previously said.

A team of scientists from the university exposed crows in Seattle to a 'dangerous face' by wearing a mask while trapping, banding and releasing birds at five sites.

Over a five-year period after the trapping had stopped, they found that the mask received an increasingly hostile response from birds in the area - suggesting that the captured birds had been able to warn others.

Dr Marzluff added: 'Because human actions often threaten animals, learning socially about individual people's habits would be advantageous.

'The number of crows scolding the dangerous mask continued to increase for five years after trapping, as expected if social learning or social stimulation were present.

'As we conducted trials, walking with the dangerous mask along the route, our actions presented opportunities for crows to observe or be stimulated by scolding.

'The number of crows encountered was consistent across trials, but the number that scolded the dangerous mask increased steadily.'