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City mouse vs. country mouse: Study finds urban animals develop larger brains

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Mammal specimens
Mice skulls, like these two from the University of Minnesota's mammal collection, were compared in a recently-published study by Professor Emilie Snell-Rood that found that braincases of urban mice are bigger than their rural counterparts Monday, Aug. 26, 2013 in St. Paul, Minn.
MPR Photo/Jennifer Simonson

Researchers at the University of Minnesota have found evidence that some wild animals living in urban areas develop larger brains than their rural counterparts.

Dr. Emilie Snell-Rood, a biologist at the University of Minnesota, examined ten species native to Minnesota by looking at skulls collected at the Bell Museum of Natural History. The brain cavities of two of the species -- the white-footed mouse and the meadow vole -- were about 6 percent larger in urban animals. 

Snell-Rood said the larger brains might allow animals to better cope with challenges, like traffic, that accompany human development. 

"Relative to what animals may have seen over the last several million years, a city or human environment is completely different," Snell-Rood said. "Having some kind of flexibility in behavior might be beneficial in that sort of environment." 

Mice specimens
Mice specimens from the University of Minnesota's mammal collection were used in Professor Emilie Snell-Rood's research Monday, Aug. 26, 2013 on the St. Paul campus.
MPR Photo/Jennifer Simonson

It isn't the first time that researchers have discovered differences between urban and rural animals. Studies have found that some birds change the frequencies of their songs in cities to stand out from urban noise. The growth of urban animals' brain cavities also could be due to nutritional changes in city living or genes. 

"We can speculate that maybe it has to do with exploring new food sources, [or] some of the challenging spatial navigation that might come through going through your town or house or yard," Snell-Rood said. 

The study also found significant cranial growth over the last century for some rural species like bats and shrews, which Snell-Rood said could be due to the fact that the animals need to travel further to find food as humans dominated the landscape. She said the study's results could be relevant to debates about conservation. 

Bat specimens
Bat specimens, like these from the mammal collection at the University of Minnesota, were used in Professor Emilie Snell-Rood's research Monday, Aug. 26, 2013 in St. Paul. She found that skull sizes increased over the last 90 years among bats living in rural areas where humans have affected the environment.
MPR Photo/Jennifer Simonson

"This kind of work highlights, at least for some species, they are sort of coping with humans," Snell-Rood said. "But some of the other species, the ones that we never see in cities, those are the ones that we need to think about: how we can help conserve that biodiversity?"

Snell-Rood said there's still much research to be done in the area, including studies of whether urban Minnesota species differ from animals in cities on the East Coast. But she notes, just because an animal's brain is larger, doesn't mean it's smarter.

Interview transcribed by Jon Collins, MPR News.