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Are some birds as clever as chimps?

Stealthy scrub-jays display social intelligence to rival great apes

24 September 2009

They say “It takes a thief to know a thief”, but what was thought to be folklore has been shown to be literally true in certain species of birds.

Western scrub-jays like to cache food for the future by burying it, and they also steal food from other birds’ caches, after which they learn to go to great lengths to protect their own caches away from prying eyes.

Such behaviour is driven by visual cues. But scrub jays are also songbirds, so Nicky Clayton’s group at the University of Cambridge wondered if scrub-jays would also respond to auditory cues when hiding their food.

To test this hypothesis, Clayton, Gert Stulp and colleagues set up test conditions where the jays could stash food under three conditions, namely when unobserved, when seen and heard, and when heard but not seen. Under each condition the birds were presented with two different substrates to bury their food: small stones that made a sound and constituted the ‘noisy’ substrate, and a finer mix of soil that could be manipulated silently.

  Are some birds as clever as chimps?

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Video transcript - Video and audio help

Sure enough, when the jays could only be heard but not seen they chose the silent substrate over the noisier pebbles. In the other test conditions, the jays chose the noisy substrate (ref 1). “We’re arguing that they know when to conceal auditory info, and when to be quiet as a mouse,” says Clayton.

Thomas Bugnyar, a cognitive biologist at the University of Vienna, also studies cognitive skills in birds. He says Clayton’s study is good evidence that audio cues are being used. “The data clearly point in this direction. The birds could be choosing the silent tray to listen to potential competitors, but this alternative calls for follow-up studies.”

Interestingly, in the unobserved and unheard (control) condition the birds used the noisy substrate when they could use the quiet one, just in case they were being overheard by another bird. Are they missing a trick? Perhaps not. Clayton suggests that by using the noisy substrate, the jays might subsequently be able to hear when other birds are pilfering their cache. “A bit like setting a car alarm,” Clayton suggests.

Clever Corvids

Scrub-jays are members of the Corvidae family that includes the rooks, crows and ravens, all birds known for performing complex behaviours. Far from being ‘bird brains’, ravens and jays are the only food-storers known to use observational spatial memory to remember the whereabouts of other birds’ food caches. “Experienced jays who have had a lot of opportunities to find their own food and steal other birds’ food go to great lengths to protect their cache,” says Clayton. “So if other birds are watching when caching they move it to new hiding places that the other birds don’t know about.”

A scrub-jay caching in the ‘quiet’ substrate

Other anti-theft devices employed by the canny birds include caching far away from an observer, behind an object, or in the shade (ref 2), and what’s more it is only the experienced thieves which do so (ref 3). “This is thought to be a complex theory of mind called experience projection,” says Clayton. “Because of past experience you have to protect your cache from the likelihood of being stolen by other potential thieves”.

In other species thieving is opportunistic. Animals stumble upon a cache by chance, or bully the food from a subordinate member of their species at the time of caching if they’re dominant.

Clayton says that with observational memory the chance of success is much greater as the bird doesn’t have to rely on being there at right time, or being dominant. “That probably set in motion increased cognitive tactics,” she says.

For instance, Clayton’s group showed in 2006 that individuals keep track of who is watching, and change their strategy depending on whether partner is watching or a competitor, and change that strategy depending on whether competitor is subservient or dominant (ref 4). Furthermore, Bugnyar has found evidence that suggests ravens modify their cache protection and pilfer tactics not just on the recognition of individuals and their dominance, but also on the inferred view of these individuals (ref 5). “They clearly know who was watching at which time,” he says.

As social birds, being caught thieving against the established hierarchy could be a matter of life and death for the jays. If you keep the birds together in a group only the dominant pair (jays mate for life and do not steal from each other) will cache. If you remove the alpha pair, the beta couple will start to cache. But if a subordinate bird steals from a bird above its station, all hell can break loose. “The pair attack the bird and pin it down and feathers fly. It can get quite nasty,” says Clayton, who adds that in extreme, but rare, incidences conflict can lead to fatalities.

This bird has shown

This social lifestyle, plus competition and conflict for food, coupled with a large brain compared to body size has lead to advanced cognitive development in Corvids that outstrips anything seen in other bird families. But Clayton goes further and says they are as intelligent as the great apes. “We argue that this is individual or convergent evolution of intelligence in two very disparate groups,” she says. “That they may have had similar selection pressures in terms of living in a complex social world and physical challenges”

So does this make the birds conscious? It’s a point Clayton refuses to be drawn on. “I don’t know how to test whether they are conscious or not,” she says. “I’m only making claims about intelligence. My colleague Nathan Emery and I have been arguing since 2004 that Corvids are as intelligent as chimps (ref 6).”

Social lifestyles lead to increased intelligence. Image: T. Lersch/Wikipedia commons

However, Bugnyar says that it depends on what exactly you mean with conscious. “But judged by their flexible behaviour, I'd say yes – at least to some extent.”

His group have shown that birds can follow the gaze of an experimenter, and even reposition themselves to follow the experimenter's gaze around a barrier (ref 7). “The original studies were with human experimenters but we've replicated things with conspecific models as well,” he says.

By rook or crook

Clayton thinks that there might be some useful parallels between birds and criminal behaviour in humans. It’s telling that the proverb “It takes a thief to know a thief” has been demonstrated in another species, when it has its origins in human behaviour. “If you’ve been burgled you are more clued in to the tricks of the trade, she says. “And ex-thieves often later help police and talk about tactics.”

Nicky Padfield, a lecturer in criminal law at the University of Cambridge, says that the paper is fascinating. She says the thought that criminologists might learn from bird studies, and that bird behavioural scientists might start asking the questions that criminologists are asking of humans is really interesting. “For example, do male birds burgle more than female? Do they burgle more or less with age? Do those who are hungry steal more than those who aren't?”

To answer similar questions, Clayton and her colleague Jim Russell are testing young children, namely in pre-schoolers before language skills are fully developed, with the experimental models developed for the scrub jays. “Do young children know when to conceal auditory information?” she asks. “Aged about four they get complex social cognition, which is also same time they develop the ability to think about the past and plan for the future.”

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  1. Western scrub-jays conceal auditory information when competitors can hear but cannot see (external link)
  2. Social cognition by food-caching corvids: the western scrub-jay as a natural psychologist (external link)
  3. Effects of experience and social context on prospective caching strategies in scrub jays (external link)
  4. Food-caching western scrub-jays keep track of who was watching when (external link)
  5. Observational learning and the raiding of food caches in ravens (external link)
  6. The mentality of crows. Convergent evolution of intelligence in corvids and apes (external link)
  7. Ravens, Corvus corax, follow gaze direction of humans around obstacles (external link)


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