CSI crows: What the birds learn from their dead

Crows pay attention to other dead crows, not to mourn, but in an effort to understand what happened, according to a new study.

Crows, it turns out, are quite observant, especially when it comes to their dead. 

While superstition has often played into the image of the cunning black bird, new research suggests crows commonly pay attention to their dead not to mourn, but in an effort to understand what happened, so the birds still living may avoid a possible threat in the future. It's a survival tactic.

The study tracked observable behaviors like crows calling to each other and gathering around the deceased, says Kaeli Swift, a Ph.D student in environmental science who co-authored the study, which was published earlier this month in Animal Behaviour (paywall). 

American crows, or Corvus brachyrhynchos, the study found, tend to wait before approaching feeding areas where they had seen one of their own dead and to observe potential predators (in this case, human volunteers) nearby. 

Such recognition, according to the study, required just one interaction at the feeding site, and the association with danger could last up to six weeks, suggesting that crows understand the concept of death and can learn and recall possible threats.

Ms. Swift started her two year study by first attracting crows by putting out food to promote nesting and breeding in hundreds of sites across the state of Washington. 

Then, she called in the masked volunteers.

In all, 25 people put on masks to obscure their faces (crows have proven to be shrewd at face recognition) and Swift "asked them to stand near the food for 30 minutes, in clear view of the crows. The masks obscured the volunteers' facial expressions, as well as allowed a rotating cast of people to be involved in the experiment," National Geographic reports. 

Some volunteers stood near a dead red-tailed hawk, a predator of the crow, holding a dead crow. Others stood by a dead red-tailed hawk empty-handed. Sometimes volunteers would hold a dead pigeon, to gauge if another bird, but not another crow, might elicit a response. The control for the experiment was just a masked volunteer, lingering near the feeding areas, with no dead hawk or crow in sight.

Of the four scenarios, in instances where death was present, the crows responded nearly every time by letting out a caw to other crows and to the volunteers, an alert known as "scolding", and would avoid feeding that day from one of Swift's locations, or mobbing nearby in large groups to assert dominance over potential predators. 

According to Swift, "of the four situations, the hawk-and-dead-crow combination provoked the most reaction. The crows did not react to the empty-handed control volunteer." 

Crows are not the only nonhuman animals to appear to understand death and its causes to some degree. A growing body of evidence shows that chimps, elephants, and dolphins may even mourn their dead. 

"This work is another example of how crows have evolved to live so successfully with us," Swift told BBC Earth. "They can learn our faces and do so in an impressive number of circumstances including when we have appeared to out ourselves as one of those prickly neighbours by interacting with their dead."