Humans have always had an uneasy relationship with crows. While admired for their legendary intelligence, they are also despised as agricultural pests and feared as harbingers of death – human death, that is. But what about crow death? Here too, crow behaviors have long puzzled and fascinated. Draped in black, crows attend funerals for fallen conspecifics. Is it because they are simply morose? Or might it be that dead crows can still speak to the living, silently imparting wisdom from the grave about the manner and context of their demise?
To address these issues, Kaili Swift and John Marzluff from the University of Washington, USA, carried out a series of experiments that are as clever as they are creepy. First, to gain the trust of breeding pairs of crows, Swift plied the birds with a favorite snack of peanuts and cheese puffs. Then, a few days later and in sight of the resident pair, volunteers in expressionless facemasks showed up next to the food pile carrying dead taxidermy-stuffed crows in their outstretched hands! As if this weren't traumatic enough (to both crows and people alike), these macabre scenes were sometimes paired with a stuffed hawk, one of the crow's most feared predators.
The responses to these stimuli were markedly different. While a dead crow held aloft by a masked volunteer drew the unquestioned ire of the resident pair of crows, their ‘scolding’ only occasionally attracted the attention of neighboring crows. By contrast, when crows were confronted with a dead crow paired with a stuffed hawk, ‘mobs’ of crows invariably formed that contained crows recruited from outside the territory of the breeding pair. Moreover, these mobs tended to be larger and more persistent, thus maximizing the scolding.
Perhaps this isn't overly surprising. After all, hawks eat crows and crows are smart enough to put 2 and 2 together: dead crow+hawk=killer hawk! But what is especially neat about this experiment is that this contextual learning extended to the volunteer in the mask.
In the 6 weeks following the main experiment, a volunteer appeared once a week with food while wearing the same mask as in the original exposure. Remarkably, even after a 6 week interval, more than a third of crows continued to mob and scold the masked person. In short, the crows had learned that this person was a potential predator, both through her association with the dead crow and also through her association with the hawk. Thus, not only are crows capable of assigning guilt by association but also their memory of these associations can potentially persist for months or longer.
So what does this mean for crow funerals? Are crows morose or unduly saddened by death? Perhaps – but probably not. When the team repeated the experiment with a dead pigeon instead of a dead crow, the crows weren't much bothered. Instead, it seems that crows gather around their dead to gain insight into how to avoid a similar fate. And by this approach, even if the threat is a new one, say a creepy masked PhD student, crows can quickly learn to respond with suitable caution. After all, why risk death for a pile of peanuts?