House sparrows are known to gain access to shopping malls by flying in front of sensors that operate sliding doors, whilst herons have been shown to be adept fishers using baits and lures.

Intelligence in birds

The insult of “bird-brain” has greatly lost its force with the recognition that there is a definite scale of intelligence amongst the birds, with the crows (including the famous New Caledonian Crows, ravens and scrub-jays) and parrots (as well as the hornbills) standing out as being conspicuously smart. Birds such as woodpeckers and owls also can score high for intelligence. These instances are also of interest because unlike most crows and parrots, which are highly social and gregarious, these latter birds are solitary. This has important implications on whether intelligence is typically manifested, if not facilitated by sociality, which is evidently not the case because of other instances, notably the solitary octopus. We need to be careful, however, not to dismiss other groups when it comes to intelligence. For example, house sparrows are known to gain access to shopping malls by flying in front of sensors that operate sliding doors, whilst herons have been shown to be adept fishers using baits and lures, which can include the deliberate snapping of twigs.

Tool use and social play

In the context of evolutionary convergence studies of birds are proving of considerable importance, both in terms of specifics and generalities. With respect to specifics amongst the most important factors are the independent evolution of tool use and social play. In both instances we find striking similarities to mammals, notably the primates. In terms of social play, whilst it is highly characteristic of young mammals, it appears to be more restricted to the more intelligent birds (thus crows, hornbills, parrots). The convergence though is striking with a one-to-one correspondence to the four principal categories of play: chasing, fighting, invitation and object play. Amongst the parrots the New Zealand kea and kakapo are especially remarkable, with the latter behaving alarmingly like a dog by rolling over on its back and waving its feet in the air as a play invitation. Kea are also celebrated, not least as going around in juvenile gangs trashing things. Aerial chases and acrobatics are well-known in ravens and hornbills, as are tug-war, not to mention skiing (in ravens) and bill-wrestling (in hornbills). Given these convergences it is less surprising that some birds appear to show co-operative hunting.

Cognition and the avian brain

With respect to generalities the recognition of striking degrees of intelligence in the birds has led to discussion as to the extent of convergence between the cognitive maps of the birds, notably the crows, and the primates, especially the great apes. Key aspects of these, of course, include learning (including that involving song or music) and memory (notably for food caching), as well as aspects of innovation and flexibility. Most exciting in this context is the growing realization that at least some birds possess a Theory of Mind, are conscious, and live in a mental world where past and future, as well as self, are realities. So too there is some evidence that at least amongst the parrots they are possibly capable of mirror self-recognition, as in bonobos, dolphins and elephants. We should also be less surprised for evidence of mental illness in such birds as the parrots that are similar to abnormal repetitive behaviour and chronic schizophrenia.

Not only is the convergence of cognitive worlds very striking and echoes that of not only the great apes but also the dolphins, but of particular importance is the redescription of the structure of the avian brain (see in particular The Avian Brain Nomenclature Consortium) that has led to a radical reappraisal as to the degrees of similarity to the mammalian brain. To the first approximation the differences are very substantial and attempts to find direct homologies between such areas as the prefrontal cortex are now agreed to be inappropriate (although not homologous, the primate prefrontal cortex may be functionally equivalent, or analogous, to the nidipalium of the bird brain). Nevertheless, convergences still emerge such as the left-sided visuo-spatial bias in both birds and humans. Despite the so-called nuclear structure of the bird brain, with its radical differences in neural organization, effectively the same cognitive map emerges. In these discussions an obvious point of comparison is whether we find a similar story to the mammals in terms of brain-size increase. The comparison is not straightforward because the body weight of birds is highly constrained by the exigencies of flight (and indeed in certain cases brain mass can alter seasonally); moreover somewhat counter-intuitively the flightless birds have, if anything, smaller than average brains. Nevertheless, there is evidence that the smarter birds do possess somewhat larger brains.