Low motivation drives poor performance of infected, anorexic crows on a string-pulling task

There is growing concern that infectious disease can impair the cognitive performance of wild animals, but the mechanisms by which this may occur are unclear. Here, we examined the apparent contributions of cognitive and motivational factors to the poor performance on a string-pulling task among American crows (Corvus brachyrhynchos) infected with a common bacterial pathogen (Campylobacter spp.). In a sample of 57 crows, of which 65% were infected with Campylobacter, we found that infected crows were significantly less likely to solve a string-pulling task with a food reward and took longer to solve it after engaging with the task. However, their poor performance appeared largely motivational. Infected birds exhibited longer latency to attempt the task (9.0 ± 2.8 vs. 22.8 ± 3.4 min when uninfected vs. infected, respectively). They also had a slower attempt rate after initial engagement (lower persistence) than uninfected crows: on average, the attempt rate of infected birds was 61% lower than for uninfected birds. Anorexia may have played a role in this lower motivation, as infected crows consumed significantly fewer calories when food was provided ad libitum than uninfected crows: birds with the highest apparent infection intensity ate 43.4% fewer calories/day than uninfected birds. Our study provides a framework for distinguishing among the potential mechanisms underlying impaired performance on a problem-solving task among infected individuals. It also sheds light on some of the potential downstream fitness and survival consequences for animals exhibiting disease-linked changes in behavior and cognitive performance.