‘Ripple effects’ of urban environmental characteristics on cognitive performances in Eurasian red squirrels

Urban areas are expanding exponentially, leading more wildlife species to reside and settle in this environment. Urban environmental characteristics, such as human disturbance or green coverage, have been shown to affect some cognitive abilities such as innovative problem-solving performance of wildlife species. However, an untested hypothesis is that due to the shared underlying cognitive mechanisms, these affected performances may induce a ‘ripple’ effect, and continue to affect other related cognitive processes (the ripple effect hypothesis). We tested this hypothesis by targeting two cognitive abilities, generalisation and memory, that overlap the cognitive mechanisms (learning and memory) of the original problem solving task in urban Eurasian red squirrels. These squirrels reside in 11 urban areas where they had previously repeatedly solved the original task (the innovators), and that their solving performance in the original task was affected by the selected urban environmental characteristics. We presented two established food-extraction tasks to the innovators to measure their performance in applying the learned successful solutions when solving a similar but novel problem (i.e., generalisation process) and recalling the learned solution of the original problem when solving the same task after an extended period of time (i.e., memory). Our results provide more detailed information to refine the hypothesis; the initial effects of urban environmental characteristics on the performance of the original task affect performance at individual level but not at population level. These affected performance includes individuals’ generalisation solving latency across successes as well as their first solving latency in the memory task. Urban environmental characteristics affect solving performance at both population and individual levels. Some environmental characteristics such as direct and indirect human disturbance affect the success of solving the generalisation task and the memory task at site level whereas other environmental characteristics such as green coverage affect the individuals’ solving latency in both tasks. Overall, our results support the ripple effect hypothesis, indicating that urban environmental characteristics have a more global impact on shaping cognitive performance than previously has shown, and thus provide a better understanding of the mechanism that supports wildlife in adapting to urban environments.