Infection impairs problem-solving performance in American crows

Abstract

Cognition is likely to have fundamental effects on the behaviour and fitness of animals, but measuring cognitive abilities can be a challenge because performance on cognitive tests can be influenced by ‘noncognitive’ factors. Parasitic infections, for example, could lead to temporary changes in the ability or motivation of an individual to participate in cognitive tasks, thereby altering cognitive performance. Here, we examine the relationship between problem-solving performance of American crows, Corvus brachyrhynchos , in a string-pulling task and their infection status with Campylobacter jejuni , a common bacterial pathogen that is taxonomically and geographically widespread in birds. Sixty-five per cent of the 34 test subjects solved the string-pulling task and temporal repeatability of individual cognitive performance across trials was high. Birds infected with Campylobacter (constituting 62% of the 21 birds tested for the pathogen) were significantly less likely to solve the string-pulling task. This difference appeared to be due to both a willingness to attempt the task and an ability to solve it: all uninfected birds attempted and succeeded in the task, whereas only seven of the 13 infected birds attempted the task, three of which failed. Overall, less active birds were less likely to solve cognitive tests, but infected birds were not generally less active than uninfected birds, suggesting that lethargy did not mediate the relationship between infection and cognitive performance. These data indicate that transient changes in health, mediated by parasites like Campylobacter , could contribute to the failure of some individuals to participate in or solve cognitive tests, although it is unclear whether impaired problem-solving performance is due to an overall lack of interest in food or an unwillingness or inability to engage in cognitively challenging tasks when infected. If the latter, impaired cognitive performance could constitute a subtle, indirect cost of infection that exacerbates the direct physiological consequences of parasites like Campylobacter . • We examined Campylobacter infection and problem-solving performance in crows. • Campylobacter -infected crows were less likely to solve a string-pulling task. • Poor performance reflected unwillingness to attempt and inability to solve tasks. • Less active crows were less likely to solve tasks. • Impaired cognition could constitute a subtle, indirect cost of infection.