The unpredictable nature of cities makes some animals better than others at responding to changes in their environment. But, there are very few studies that examine which aspects of city life influence the flexibility of an animal's behavior. Recent work by Pizza Ka Yee Chow from Max Planck Institute for Ornithology, Germany, and an international team of colleagues from Japan, the UK, the USA and Germany suggests that urban environments can hinder the Eurasian red squirrels’ problem-solving abilities. To investigate how different characteristics of a modern human settlement affect squirrels’ adaptability, the team created puzzles for the rodents to solve, across the city of Obihiro, Japan.
First, the team selected 11 sites around the city that differ in the number of human passers-by, man-made buildings and grassy areas. The researchers used Google Maps to determine the size of each site, the number of neighboring buildings and the amount of green space. To get a sense of the number of humans a squirrel might encounter at each site, a researcher recorded the number of people in the area 5 times a day, rain or shine, for about a month. The scientists also set up cameras to determine the number of individual squirrels living in each area.
Next, Chow and colleagues built food puzzles to test the squirrels’ problem-solving skills. The puzzles consisted of clear Plexiglas boxes with a series of levers that squirrels could push or pull with their nose, teeth or paws to release hazelnuts trapped inside. Using a camera placed nearby, the team measured how many squirrels were able to solve the puzzle, how long it took them to succeed, and how well each squirrel learned a puzzle's solution.
It turned out that squirrels in areas where there were fewer people or buildings were, on average, more successful at extracting nuts from the plastic contraptions. When there were fewer passers-by and towering structures, more squirrels solved the puzzle on their first attempt. More people and buildings, in contrast, led to fewer successful squirrels. This suggests that human disturbance negatively impacts a squirrel's problem-solving abilities in cities.
Surprisingly, the researchers discovered that the squirrels reacted in one of two ways to throngs of people. They either failed to get the nuts from the boxes or became masterminds that rapidly deciphered the food puzzles. This suggests that urban squirrels either are prepared to spend time learning to solve problems in return for delicious nuts or will put up with any old food they can find easily, no matter how inferior. The rapid pace at which some squirrels solved the puzzles might also be caused by pressure they feel to work quickly before someone approaches.
The researchers also examined whether the size of local squirrel populations affects an individual's flexibility and discovered that squirrels in areas with lots of other squirrels were worse at solving problems, but a handful of individuals could solve the puzzle rapidly. This means that competition between squirrels for food further deepens the divide between the few speedy squirrels that are great at finding food and those that can't distinguish push from pull. In addition, the amount of grass in city areas didn't affect the squirrels’ adaptability, but squirrels in concrete jungles were very slow learners. This suggests that a lack of green space could be a stressor, though it doesn't directly impact squirrels’ problem-solving performance.
As cities continue to expand across the globe, policymakers need to understand how urban environments influence an animal's ability to adapt to change and to survive. For Eurasian red squirrels, human disturbances in the presence of other squirrels impair the essential skills that are necessary for them to find food.
