Have you ever stared into the eyes of an animal and wondered ‘what are you thinking’? Yeah, me too.
There are lots of ways that scientists have tried to understand animals, studying their behaviours and responses, learning their languages and cultures, scanning their brains, the list goes on. But one idea that fascinated me to learn about was the idea of brain lateralisation.
Brain lateralisation is defined as the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other.
The vertebrate (animals with a backbone) brain is separated into two hemispheres, left and right, each with specialized functions.
Studies have shown that vertebrates respond to situations using different sides of their brains, depending on the situation or environment that they are in. This is called a lateralised response.
Rogers (2008) states that the left hemisphere of the brain is involved in learning and controlling non-stressful situations, whereas the right side is used to respond to more stressful situations such as escaping from predators.
So how does this all relate to what a bird is thinking?
By creating different scenarios, scientists have been able to work out whether a bird responds differently to threatening vs non-threatening stimuli. They can identify this by observing which eye (left or right) the birds use predominantly.
This is because a right eye is linked to the left side of the brain, and a left eye is linked to the right side of the brain. So when a bird uses its left eye to inspect an object or environment, this means it uses the right lobe of the brain, and vice versa. And as we now know, each hemisphere of the brain deals with different situations.
This also means that by observing which eye a bird is mostly using to inspect an object, we can take a guess of how the bird is perceiving that object. That is, whether it perceives it as a threat or non-threat. An example of a threat could be predator, and a non-threat could be a food item.
There are several examples of studies on brain lateralisation in birds. Such as an observational study of American tree sparrows and Dark-eyed juncos conducted by Franklin and Lima (2001). They found that each species would turn their heads to use their preferred eye when faced with a visual obstruction (or a potential threat) (Franklin and Lima, 2001).
In another experiment by Ulrich et al. (1999) homing pigeons were tested to see if the birds had a lateralized preference for eye use, and therefore asymmetrical hemisphere utilization in the brain. Their results demonstrated a preferred use of the right eye, therefore the left hemisphere of the brain, in pigeons that showed substantially better homing abilities.
Ventolini et al. (2005) found a preferential use of the right hemisphere (left eye) during predatory behaviour, but a left hemisphere (right eye) preference during courtship behaviour in the black-winged stilt.
Furthermore, a study by Rogers and Kaplan (2006) shows a preferential response of the Australian magpie to view predators on their left side (left eye / right hemisphere), and prey on their right (right eye / left hemisphere).
Cerebral lateralization is well documented in both vertebrates and invertebrates (Rogers, 2008) so it would be interesting to examine how far back in the evolution of animals, lateralization in auditory processing is present.
Of course, we will never know what really goes on inside another’s mind, but we can certainly try! So next time a seagull flies over your head whilst you’re just about to tuck into your fish and chips at the seaside – take note of which eye it’s looking at you with, then you might be able to have a guess if it’s about to steal a chip!
References:
Franklin, W.E., and Lima, S.L. 2001. Laterality in avian vigilance: do sparrows have a favourite eye? Animal Behaviour 62: 879-885.
Rogers, L.J. 2008. Development and function of lateralization in the avian brain. Brain Research Bulletin 76 (1): 235–244.
Rogers, L. J., and Kaplan, G. 2006. An eye for a predator: lateralization in birds, with particular reference to the Australian magpie. In: Malashichev, Y.B., Deckel, A.W., (eds) Behavioral and morphological asymmetries in vertebrates. Landes Bioscience, George Town: 47-57.
Ulrich, C., Prior, H., Duka, T., Leshchins’ka, I., Valenti, P., Gunturkun, O., and Lipp, H.P. 1999. Left-hemispheric superiority for visuospatial orientation in homing pigeons. Behavioural Brain Research 104 (1-2): 169-178.
Ventolini, N., Ferrero, E.A., Sponza, S., Chiesa, A.D., Zucca, P., and Vallortigara, G. 2005. Laterality in the wild: preferential hemifield use during predatory and sexual behaviour in the black-winged stilt. Animal Behaviour 69: 1077-1084.