What does it feel like to be a bird? Though this might be asked more often by children than by adults, it is a valid scientific question. In September, a Royal Society meeting on bird senses will seek an answer.
The aim of the gathering, in Buckinghamshire, will be to examine our understanding of how birds interact with the world – through all of their six (or more) senses – and even to gain insights into the kinds of emotional reactions they have to their surroundings.
Attributing emotions to birds is not a flight of fancy. Emotions are a feature of evolution: they arose to help creatures navigate the world safely and with maximum reward. Though it is hard to read joy in a jay, there is much evidence that birds experience negative emotions, at any rate, such as the expectation of harm or punishment. Though we might call it fear, we know nothing of a bird’s subjective state, so the scientists working in this field are reluctant to give it that label. Nonetheless, it is a useful area of research: further investigation might tell us things (things we might rather not know) about the state of mind of a battery hen.
The extra sense (or senses) available to birds are similarly tricky to explore. For instance, it is impossible for us to imagine what it is like to sense a magnetic field.
So far, mostly by playing tricks on robins, we have worked out that this sense requires certain inputs. It works only when the field has an intensity within a fairly narrow range. If the field is too strong, or too weak, the bird cannot navigate. The same problem arises if the sky is too light or too dark. The light at dusk, in which blue-green is the dominant colour, makes magnetic navigation easiest.
Most bizarrely of all, the light – for robins, at least – has to be seen with the right eye. Cover the left eye and a bird can still navigate. Swap the blindfold to the right eye and it will remain for ever lost. The best explanation at present for this set of working conditions involves some extremely intricate physics taking place in a robin’s retina – blue-green light seems to trigger changes at an atomic level in the right eye.
While we work out the details, there are plenty of other puzzles, such as what tastes good to a bird. Many animals have a smaller selection of taste receptors than human beings. Those that are exclusively carnivores don’t have sweet receptors. Giant pandas have a sweet tooth but are unable to register the taste of amino acids – also known (to us) as umami. Sea lions, dolphins and whales have lost a plethora of taste receptors and possibly have none left at all, so eating might be a purely functional, rather joyless activity for these creatures. Birds may be in a similar position. They have fewer taste buds than most mammals do, which suggests they don’t taste much at all.
Smell is another important sense for birds. Some sniff the air in order to find their way home. Homing pigeons deprived of their sense of smell are unable to navigate after release from an unfamiliar location. Others use smell to identify food sources.
More surprising is that birds can ascertain each other’s sex, species and identity just from its smell. Then there are the mate-attracting smells: crested auklets have a lemony smell that advertises their hygienic status. This citrus odour is associated with a resistance to infection by lice, a desirable trait in a potential mate.
So now we have the answer to the vexing question of how a bird smells – pretty good, sometimes.