Do infected crows struggle with puzzles because of cognitive difficulties or because they are less motivated to try?

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There is growing concern that infectious disease can impair wild animals’ cognitive performance, but how this might happen remains unclear.

Researchers examined the apparent contributions of cognitive and motivational factors to poor performance on a string-pulling task in American crows (Corvus brachyrhynchos) infected with the common bacterial pathogen Campylobacter spp. The study compared infected and uninfected crows on a task with a food reward and assessed calorie consumption when food was freely available (ad libitum).

The sample included 57 crows, 65% of which were infected with Campylobacter. Infected crows were significantly less likely to solve the string-pulling task and took longer to solve it after engaging with it.

However, their poor performance appeared largely motivational, rather than clearly demonstrating cognitive difficulties.

The time before first attempting the task was longer in infected birds: 9.0 ± 2.8 minutes for uninfected crows versus 22.8 ± 3.4 minutes for infected crows.

After first engaging with the task, infected crows also attempted it at a slower rate, indicating lower persistence. Their average attempt rate was 61% lower than that of uninfected crows.

Reduced appetite may have contributed to this lower motivation. When food was available ad libitum, infected crows consumed significantly fewer calories than uninfected crows; birds with the highest apparent infection intensity ate 43.4% fewer calories/day than uninfected birds.

The study provides a framework for distinguishing among potential mechanisms underlying impaired problem-solving task performance in infected individuals.

It also sheds light on potential downstream consequences for fitness and survival in animals showing disease-linked changes in behavior and cognitive performance.