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

Urban environmental characteristics such as direct human disturbance have been shown to create a double-edged sword effect on wildlife’s ability to solve novel problems (1). However, these characteristics would continue to affect related cognitive processes (the ‘ripple effect hypothesis’). Here, we demonstrate this in urban Eurasian red squirrels who have previously learned a successful solution for a food-extraction problem (the innovators) by using two established food-extraction problems. One of the problems assesses the generalisation process (applying the learned solution when solving a similar but novel problem) and another problem examining memory for the learned solution of the original problem. The innovators significantly improve their solving latency on their 3rd success, and efficiently solve the generalisation problem from the 5th success onward. They also quickly recall the learned solution for the original problem in the memory test. While urban environmental characteristics do not affect the innovators’ ability to solve either problem, characteristics like direct human disturbance enhance the innovators’ learning speed for the generalisation problem, first recall and recall speed in the memory test. Path analyses show that direct human disturbance and to a lesser extent, area of green coverage are the major variables affecting cognitive performance. Our results highlight that some urban environmental characteristics can induce a far-reaching impact on shaping cognitive performance, as well as provide direct evidence for better understanding the mechanism that supports wildlife in adapting to urban environments.