Some animal behaviours have a strong influence on the fitness of individuals, such as the ability to reject foreign eggs displayed by avian species hosts of brood parasites. This behaviour, that reduces the costs of parasitism, is complex from a cognitive perspective, because individuals must distinguish their own eggs from parasite eggs, using different cognitive skills such as learning, memory and decision-making. Many cognitive processes are positively related at the individual level, suggesting the existence of some degree of “general intelligence”, which varies between individuals.

The brain processes, stores and integrates different types of information, and it is likely that cognitive abilities correlate with the size of the brain, or some of its areas; however, so far studies of the cognitive ecology of birds have been based on comparative approaches between species relating the size of the brain or some of its areas with cognitive traits. Furthermore, egg-rejecting behaviour has rarely been considered in a cognitive context, nor has the possibility that differences in the expression of rejection between individuals could be due to differences in cognitive function or brain size. Some brood parasite hosts, such as the magpie (Pica pica), have large brains and complex cognitive abilities, but it is not known whether inter-individual differences in the size of the brain or its areas are related to individual variation in cognitive abilities (including egg rejection).

In this three-year project, we propose to explore for the first time the possible relationship between egg rejection and cognitive abilities in magpies, quantifying in the same individuals their ability to reject eggs, their performance in a set of cognitive tasks and the size of their brain and some of its areas; we also aim to determine whether cognitive performance changes with age (as it does egg rejection behaviour) and finally the fitness consequences of the variation in cognitive abilities.