Relaxing Chipmunks in Urban Areas

The human population around the world keeps growing. With that growth existing cities are expanding and new ones are being built. The urban landscape is a relatively new environment with different ecological and environmental conditions compared to rural areas. Environmental pressures in cities affect humans and wild animals alike, for example artificial light at night and air pollution and more noise due to traffic and human activity. Many urban animals have adaptations in order to live there: changes in behaviour, morphology, and physiology are common. One species that exemplifies this is the eastern chipmunk (Tamias striatus) found in eastern North America. Eastern chipmunks live in forests but can also be found in urban green spaces. They prefer areas with plant variety: large trees, shrubs, and herbaceous ground vegetation and their diet consists of nuts, seeds, and small animals (Tranquillo et al., 2023).

Energy saving eastern chipmunk

Chipmunks have some interesting adaptations to the urban environment. Compared to populations in non-urban habitats, urban chipmunks tend to be less active and more sedentary. The reduced activity is a possible result of the abundance of food in cities, which people throw away or leave behind in every corner of streets and parks. Chipmunks thus need to spend less time finding food and have more time to rest. And maybe they are just less stressed overall, not just with respect to food. Urban chipmunks tend to clean their coat less, which suggests a reduced reaction to stressors in the environment.

What is remarkable is that the urban chipmunks are so sedentary. Animals in a novel environment typically disperse and explore their new ecosystems, but urban chipmunks do the opposite. One possible explanation is natural selection in urban areas favors this behaviour. That this might be the case is hinted at by the fact that chipmunks in a new city show different behaviours as they select a new habitat in which to live. Individuals with active behavioural phenotypes disperse more and disappear from the city while the ones that are less active stay behind. In this way, less active chipmunks that are less reactive to stress increase in abundance in urban areas (Lyons et al., 2017).

Reproductive success

Looking at morphology, most mammals become heavier in urban areas compared to the same species in rural environments. Just like with reduced activity, a possible cause for this is the increased amount of food in urban areas. The eastern chipmunk shows this change too. But interestingly, only the female eastern chipmunks have a higher body mass compared to populations in non-urban areas. This increase in female body mass may be related to reproductive success by having more energy reserves. The activity that takes the most energy of the reproduction is lactation, and access to more food allows female chipmunks to fuel lactation. This could lead to a higher reproductive success in urban areas (Lyons et al., 2017).

The eastern chipmunk is thus well adapted to the urban landscape. But in order to be able to live in the city, there are other important factors. As mentioned at the beginning, chipmunks prefer high levels of variation in vegetation. In particular, percentage of tree cover is very important since it both provides habitat and connects green spaces (Tranquillo et al., 2023). So just like humans, urban chipmunks are happy with trees and other green spaces, and they like to relax a bit more.

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References:

Lyons J, Mastromonaco G, Edwards DB, Schulte-Hostedde AI, (2017) – Fat and happy in the city: Eastern chipmunks in urban environments. Behavioral Ecology 28(6), 1464-1471. https://doi.org/10.1093/beheco/arx109

Tranquillo C, Bisi F, Wauters LA, Preatoni D, Martinoli A, Santicchia F, (2023) – The impact of urbanization on chipmunks, arboreal and flying squirrels: a global systematic review. Mammal Review ISSN 0305-1838. https://doi.org/10.1111/mam.12335