* Scientific study references are indicated in (). These can be found at the bottom of the article, and can be clicked on to access the original reports.
The term birdbrained has long since been equivalent to stupid. It gives away our ingrained assumption that birds are mindless pecking machines whose brains and the thoughts they produce, if any, couldn’t even begin to rival ours in terms of complexity.
This long-held view is partially inspired by the fact that we see fundamental differences in the structures of mammalian and bird brains. Since we know ourselves to be intelligent animals, it’s tempting to suppose that it is exclusively the mammalian brain design that is capable of producing complex thoughts and behaviours. This might be why many of us are captivated by the occasional news story describing researchers’ discovery of yet another surprisingly complex behaviour in laboratory birds. Crows that make innovative tools (2). Scrub jays that make plans for the future (1). Ravens that seem to contemplate the contents others’ minds (3). We have an undeniable fascination with seeing traces of human-like abilities in animals, and as more evidence rolls in, perhaps it’s time to ask what all of it might mean. Have we been wrong about bird brains? Could intelligent bird behaviour be underpinned by true mental complexity, or do we just read into observations through an anthropomorphic lens and delude ourselves into thinking that something human-like might be going on in the bird’s mind? Let’s start with the brain…
Revising a century of misconceptions about the bird brain
I suppose in comparison to most animal species, the organisation of the mammalian brain does indeed inspire awe. In primates, just over 70% of total brain mass is occupied by the cerebral cortex. This is a 2-3 mm thick sheet of densely packed brain cells, or neurons, which coats the entire exterior of our brains and folds into a multitude of grooves that maximise the brain tissue which can fit into our skulls. Most of the cortex, that is the evolutionarily recent neocortex, is divided into six clearly defined layers, characterised by the different types of neurons which populate them and the nature of connections they have with other brain cells.
To see examples of the layered structure of the mammalian cortex, let’s look at two images taken from mice, shown below. To obtain the left image, researchers injected developing mouse embryos with genes which resulted in separate groups of cells producing differently coloured fluorescent proteins. When these cell groups develop into distinct types of neurons and migrate to their resident locations within the cortex, we can see that they primarily inhabit distinct layers. In the right image, we see a clear layered separation between the neurons that receive signals from the mouse’s whiskers, as well as the fibres along which the information is transmitted (green), and neurons that communicate back down (orange).
The layered structure of the cortex appears to be a universal feature of all mammalian brains – one that is proposed to have considerable advantages. Firstly, such segregation likely increases the efficiency with which neurons can perform their functions, and communicate to their target neurons. Why is that? It’s quite reasonable to assume that those brain cells which have access to similar information by virtue of having similar external connections (eg. to the whiskers) must have similar jobs to do, and benefit from being able to closely communicate with each other. Thus, allowing neurons with similar properties to work in proximity with one another would reduce the need for chaotic winding connections between them and boost the speed with which information can be transformed and transmitted elsewhere. Perhaps unsurprisingly, the high degree of organisation in the mammalian brain makes it tempting to assume that the layered cortex is the cradle of sophistication, both for psychological processes and behaviours.
This view has not worked in favour of birds who, in contrast to mammals, don’t have a layered cortex. Instead, their brains are nucleated – that is, their neurons are organised in clusters (nuclei), and thus lack the structure we instinctively associate with complex function. Furthermore, one feature that has perhaps prevented bird brains from being recognised as capable of intelligence is their superficial resemblance to the so-called basal ganglia of the mammalian brain (7). The basal ganglia are a group of deep-brain cell clusters that partially underpin our ability to generate voluntary movements and acquire motor habits, such as driving, riding a bike, or playing piano (skills we often ascribe to ‘muscle memory’).
You might notice in the image above that these clusters aren’t directly connected to each other. They are interrupted by a major pathway of nerve fibres, called the internal capsule, which acts as a highway for transmitting information to and from the cortex. The running of these fibres between the cell clusters gives the basal ganglia a somewhat stripy appearance that happens to be superficially similar to the bird brain. This led the influential 19th century German anatomist, Ludwig Edinger, to assume that bird brains were primarily constructed of tissue that is related in origin and function to the mammalian basal ganglia (7). He proposed a map of the bird brain, in which most areas were named with variations of the root word ‘striatum’ (from Latin ‘striatus’ – striped). As this view became gospel, it added fuel to the already existing assumption that birds were, at most, excellent pecking machines, with the brains suited to having a repertoire of motor skills, but little capacity for thought.
This view, which dominated for about a century, has recently been revised. Researchers found that the profile of gene activity throughout much of the bird brain makes it highly likely that it actually derives from a region of the embryonic brain (pallium) that gives rise to the layered mammalian cortex (7,16). In light of these discoveries, the modern map of the avian brain reveals just how much brain territory once assumed to be striatal (green) is actually consumed by pallium-derived brain tissue (blue).
Thus, our brains and bird brains appear to be closer evolutionary relatives than we had anticipated. Researchers propose that we might have shared a common ancestral structure that was originally nucleated – much like in birds right now. In this view, the cortical layers of mammalian brains are a more recent development, likely selected because it endows the system with greater efficiency (7,8,10). It’s quite likely that this change represents a substantial biological upgrade, affording the mammalian brain an unprecedented level of capacity. And yet researchers have found some remarkable displays of intelligence in certain bird species which, in some respects, seem to place them on equal footing with primates. Could this indicate that a layered organisation does not hold the exclusive key to brainpower? Apparently clever bird behaviour raises the possibility that we could be witnessing the result of convergent evolution, in which two distinct brain designs have both arrived at intelligent solutions to producing complexity. To explore this, let’s look at some tantalising evidence that has convinced some researchers that birds might be capable of mentalising – that is, comprehending the contents of others’ minds.
‘I know what you’re thinking… Or do I?’
During courtship, male European jays like to feed their female love interests – something that researchers have used as an opportunity to test whether a male could adjust his choice of food for his mate depending on what her current preference might be (11). In one experiment, researchers manipulated which food a female might prefer on a given day by satiating her with large amounts of a particular food, assuming that this would make her temporarily tired of it and crave something different. The underlying logic of this assumption is quite solid, as they observed that a female that had just been fed plenty of waxworm and then given a chance to choose between some more waxworm or mealworm larvae, consistently preferred mealworm. In essence, novelty excites. But would her male suitor be able to infer something about her desire after watching her being fed by the researchers?
When it came down do it, the male consistently tried to feed his female with foods that differed from what he had recently seen her eating. Importantly, what he chose for his female was unrelated to what he would personally choose for himself, which makes for a truly convincing argument that he was deliberately catering to the assumed preference of his romantic interest.
The capacity to behave in a way that indicates an understanding that other individuals have their own desires is actually not clearly observed in human children until roughly the age of 18 months. We know this because of experiments in which children are asked to choose one of two food items to give an individual who seems to clearly hate one and enjoy the other (13). These studies have found that children below about 18 months of age consistently give the individual food items that they themselves prefer, with no regard for the individual’s apparent preference. Aside from this, some bird species appear to possess a social skill that humans don’t master until about four years of age – the ability to understand and exploit the fact that others might hold false beliefs. In other words, some birds appear to be skilled liars.
Deceptive intentions are apparent in the food hoarding rituals of birds such as crows and Eurasian jays, who employ various strategies to minimise the risk that the food they hide underground or in a burrow will get stolen. When hiding, or caching, their food in the presence of observers they tend to wait for them to become distracted before going through with placing the food in its hiding spot. Sometimes, these birds actually return to the site on a later occasion and re-cache their food in privacy if they did end up being watched when hiding it the first time (6). The fact that these birds go to such lengths to safeguard their hiding spots from others raises the possibility that they, on some level, understand that others might have the intention to steal.
Some researchers aren’t convinced that this evidence calls for explanations which grant birds almost human-like reasoning abilities (14). In the world of science, it’s frequently assumed that the simplest explanation is likely to be the truest. As such, resorting to anthropomorphic interpretations of seemingly clever animal behaviour is perhaps more wishful thinking than science, as it’s not the simplest possible explanation. This school of thought prefers to argue that when we interpret intelligent behaviour, there’s no need to lean back on assumptions of actual mental processes inside an animal’s head. Such a pessimistic, or just scientifically sound, perspective (depending on your own philosophy) has earned these researchers the nickname ‘killjoys’ in academic discussions of animal intelligence (4).
In an experiment that offered solid support to the ‘killjoys’, researchers found that ‘virtual’ scrub jays could actually mimic the food caching habits of real-life jays, in the absence of any mental capacity to acknowledge another bird’s intention to steal (17). The computer model of the scrub jay was programmed to follow particular simple rules of behaviour including i) a preference to hide food away from other birds and ii) a tendency to cache and re-cache food more often when stressed. The assumption that stress stimulates such behaviour is quite valid, as we have evidence that birds implanted with pellets releasing the stress hormone corticosterone tend to hide and recover food at higher rates than normal (12). Using this computer model, researchers found that their virtual scrub jays returned to relocate their food in privacy after being watched simply because the presence of an onlooker during the initial hiding event stressed them out! In one sweep, this publication seemed to obviate any need to suppose that jays might be aware of other birds’ intentions. But there’s one thing that the computer model was missing…
Researchers have pointed out that scrub jays re-locate their food in privacy only if they had themselves in the past stolen food that was hidden away by others (6). In contrast, those who had never stolen themselves weren’t particularly nervous about being watched when burying their food. In my mind, it’s quite telling that personally experiencing the intention to steal is necessary for these birds to feel nervous about being watched. It’s difficult to resist the conclusion that jays might actually be projecting their experiences onto others to infer their intentions.
Why is anthropomorphism so unorthodox?
The world of birds is brimming with evidence that these animals toy with others’ intentions and beliefs. Occasionally, crows make false hiding spots that are either empty or contain inedible items such as stones (9). In some cases, when they are being watched or followed, they feign interest in sites that they know to be empty, distracting potential thieves from real food sites (5). Interestingly, the ability to deliberately misinform doesn’t fully develop in humans until roughly four years of age. When toddlers are given an object and asked to ensure that an individual doesn’t find it, most of them don’t seem to understand the fact that deceptive ploys can be used to manipulate the internal state of the human seeking that item and trick them into looking elsewhere. In contrast, children older than four are known to be capable of effectively and intentionally laying false trails (15). Once this ability to misinform is observed, researchers are quite confident that they are witnessing the development of a complex social skill – the understanding that others have minds of their own. In light of this, I wonder why some researchers are so reluctant to accept the possibility of such mental prowess in birds that produce these exact same deceptive behaviours.
Claiming that animal behaviours might be underpinned by complex mental processes is largely seen as anthropomorphic – a sinful tendency to see human-like abilities in animals. But why does the possibility of human-like skills in other species seem so illogical? I suspect that the apparent ‘wrongness’ of anthropomorphism might be rooted in our implicit belief that our own mental abilities are a metaphorical leap over an abyss separating humans from other animals. The idea that animals might have traces of human-like mental capacities is often considered some sort of last-resort ‘magical’ explanation for apparently intelligent behaviour. Of course, we are almost certainly the most intelligent species – but is it possible that the pedestal we have built ourselves is too high? After all, both a four year old and a crow can deceive another person, and yet only the human is assumed to do so because they understand that others have minds that can be misinformed. If we believe in evolutionary continuity between various species, perhaps we should be reconsider viewing human-like capacity as an unattainable benchmark for other animals. In the words of Charles Darwin, ‘the difference between man and the higher animals, is one of degree and not kind’. Perhaps I am a romantic when it comes to interpreting clever bird behaviour. Of course, it’s purely my take, and I am curious to hear your own opinions!
P.S. For those, who are interested in further reading, here is a fascinating publication in the journal Science, describing the African fork-tailed drongo which obtains almost a quarter of its daily meals by producing false alarm cries of other species to divert them from their food.
- Clever Eurasian jays plan for the future. BBC Nature News.
- Caught on tape! Wild crows use tiny cameras to film themselves using tools. LA Times.
- Researchers find birds can theorize about the minds of others, even those they cannot see. Phys.org.
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- Bugnyar, T. and Kotrschal, K. (2003). Leading a conspecific away from food in ravens (Corvus corax)? Animal Cognition 7, 69-76.
- Emery, N. J. and Clayton, N. S. (2001). Effects of experience and social context on prospective caching strategies by scrub jays. Nature 414, 443-446.
- Emery, N. J. and Clayton, N. S. (2005). Evolution of the avian brain and intelligence. Current Biology 15: R946.
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- Ostoji, C. L. et al. (2013). Evidence suggesting that desire-state attribution may govern food sharing in Eurasian jays. Proceedings in the National Academy of Sciences USA 110, 4123–4128.
- Pravosudov, V. V. (2003). Long-term moderate elevation of corticosterone facilitates avian food-caching behaviour and enhances spatial memory. Proceedings of the Royal Society: Biological Sciences 270, 2599-2604.
- Repacholi, B. M. and Gopnik, A. (1997). Early reasoning about desires: evidence from 14- and 18-month olds. Developmental Psychology 33, 12-21.
- Shettleworth, S. J. (2010). Clever animals and killjoy explanations in comparative psychology. Trends in Cognitive Sciences 14, 477-481.
- Sodian, B. et al. (1991). Early deception and the child’s theory of mind: false trails and genuine markers. Child Development 62, 468-483.
- The Avian Brain Nomenclature Consortium (2005). Avian brains and a new understanding of vertebrate brain evolution. Nature Reviews Neuroscience 6, 151-159.
- Van der Vaart, E. et al. (2012). Corvid re-caching without ‘theory of mind’: a model. PloS ONE.