The Rodents of Chicago Are Evolving in Real Time, Scientists Say
Here's what you'll learn when you read this story:
Urbanization has had visible morphological effects on chipmunks and voles in the Chicago metro area.
While both chipmunks and voles have experienced changes to their skulls in response to urban navigation and hearing needs, chipmunks have also grown larger because of the availability of human food scraps (especially high-calorie processed foods).
Watching the changes in animals that have adapted to city environments could help us gauge how much urban sprawl has impacted these populations.
As Pizza Rat proved, some creatures can adapt to just about anything, even the concrete jungle. And it isn't just New York City—Chicago rodents have become so used to city life that they have actually evolved for urbanization.
Anyone who lives in Chicago might think nothing of a chipmunk scurrying by, but all the scraps of processed food that the local chipmunks have pilfered from human garbage cans have both made them larger than they used to be and shrunk their teeth. And as a result of all the horns honking, brakes screeching, and everything else that turns up the volume of a bustling city, voles have developed smaller inner ears to turn down the noise.
Humans have obviously had a profound impact on the environment. By studying chipmunk and vole specimens hidden away in the backroom drawers of Chicago's Field Museum of Natural History, a research team—lead by assistant curator of mammals Anderson Feijó, along with mammalogist and XCT lab manager Stephanie Smith—found that there have been morphological changes to the skulls of these animals over the last 125 years. The changes have corresponded with the growth and industrialization of the Chicago metro area.
'These different patterns between chipmunks and voles reveal species-specific responses to the same human-induced habitat changes and the need for nuanced conservation plans in the face of continuing change,' Smith and Feijó said in a study recently published in the journal Integrative and Comparative Biology.
Skulls were the focus of this research because they reflect the effects of habitat and ecology on the animals' diets, sensory systems, navigational abilities, cognitive abilities, and body sizes. Voles and chipmunks were chosen because their biologies and proximity to humans were thought to be different enough from each other to show distinct responses to urban stressors. Eastern chipmunks (Tamias striatus) are squirrel relatives, while eastern meadow voles (Microtus pennsylvanicus) are more closely related to hamsters. Most previous studies on the effects of urbanization have looked at body size, but not much else.
Feijó and Smith compared the usual habits and habitats of chipmunks and voles. Eastern chipmunks forage throughout the year in woods with thick canopies and open understories, hoarding nuts and seeds in their burrows when they hibernate in the winter. Voles live in dense grasslands, nesting on the ground and eating mostly grasses and the occasional insect. Most urban specimens were collected after 1980, while specimens from less urbanized areas were from before 1950.
After measuring different sections of specimen skulls and taking surface scans, the researchers found that both species experienced changes due to a number of factors, including temperature. The skulls of chipmunks have a wider brain case, are flatter than they used to be, and feature a longer rostrum (the frontal part of the skull containing the palate and nasal cavity), which could be a result of specific navigation needs. Their auditory bullae—bony structures near the back of the skull that protect parts of the inner ear and convert sound waves into electrical signals that are transmitted to the brain—have also shifted backward.
Like chipmunks, urban voles had flatter skulls and auditory bullae that were further back. Their auditory bullae have also shrunk as a result of needing to handle the loud, incessant noises of Chicago. While voles' average body size has remained virtually the same, other cranial bones revealed that the creatures have actually been affected by urbanization more than chipmunks. Vole skulls from more urbanized sites were not as diverse in shape as those from regions that were less urbanized, which could mean that the lower variance in closed urban environments keep voles more morphologically similar to each other.
It became obvious that chipmunks in urban areas are increasing in size, and their rows of teeth have grown shorter. The researchers think this is because more food is available throughout the year, and that chipmunks having more human interaction has put more things on the menu. Among the free meals chipmunks grab in the city are high-calorie, highly processed foods that add body weight and are easier to chew than nuts (meaning they don't need to use their teeth as much). Urban brown rats have been experiencing the same evolutionary phenomenon.
'As cities continue to sprawl and push outwards, understanding complex morphological responses to increasing urbanization and associated effects can elucidate the impact of human population growth on biota,' the researchers said. '[It can] help us forecast how wild populations will cope with continuing change in the coming decades.'
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The Rodents of Chicago Are Evolving in Real Time, Scientists Say
Here's what you'll learn when you read this story: Urbanization has had visible morphological effects on chipmunks and voles in the Chicago metro area. While both chipmunks and voles have experienced changes to their skulls in response to urban navigation and hearing needs, chipmunks have also grown larger because of the availability of human food scraps (especially high-calorie processed foods). Watching the changes in animals that have adapted to city environments could help us gauge how much urban sprawl has impacted these populations. As Pizza Rat proved, some creatures can adapt to just about anything, even the concrete jungle. And it isn't just New York City—Chicago rodents have become so used to city life that they have actually evolved for urbanization. Anyone who lives in Chicago might think nothing of a chipmunk scurrying by, but all the scraps of processed food that the local chipmunks have pilfered from human garbage cans have both made them larger than they used to be and shrunk their teeth. And as a result of all the horns honking, brakes screeching, and everything else that turns up the volume of a bustling city, voles have developed smaller inner ears to turn down the noise. Humans have obviously had a profound impact on the environment. By studying chipmunk and vole specimens hidden away in the backroom drawers of Chicago's Field Museum of Natural History, a research team—lead by assistant curator of mammals Anderson Feijó, along with mammalogist and XCT lab manager Stephanie Smith—found that there have been morphological changes to the skulls of these animals over the last 125 years. The changes have corresponded with the growth and industrialization of the Chicago metro area. 'These different patterns between chipmunks and voles reveal species-specific responses to the same human-induced habitat changes and the need for nuanced conservation plans in the face of continuing change,' Smith and Feijó said in a study recently published in the journal Integrative and Comparative Biology. Skulls were the focus of this research because they reflect the effects of habitat and ecology on the animals' diets, sensory systems, navigational abilities, cognitive abilities, and body sizes. Voles and chipmunks were chosen because their biologies and proximity to humans were thought to be different enough from each other to show distinct responses to urban stressors. Eastern chipmunks (Tamias striatus) are squirrel relatives, while eastern meadow voles (Microtus pennsylvanicus) are more closely related to hamsters. Most previous studies on the effects of urbanization have looked at body size, but not much else. Feijó and Smith compared the usual habits and habitats of chipmunks and voles. Eastern chipmunks forage throughout the year in woods with thick canopies and open understories, hoarding nuts and seeds in their burrows when they hibernate in the winter. Voles live in dense grasslands, nesting on the ground and eating mostly grasses and the occasional insect. Most urban specimens were collected after 1980, while specimens from less urbanized areas were from before 1950. After measuring different sections of specimen skulls and taking surface scans, the researchers found that both species experienced changes due to a number of factors, including temperature. The skulls of chipmunks have a wider brain case, are flatter than they used to be, and feature a longer rostrum (the frontal part of the skull containing the palate and nasal cavity), which could be a result of specific navigation needs. Their auditory bullae—bony structures near the back of the skull that protect parts of the inner ear and convert sound waves into electrical signals that are transmitted to the brain—have also shifted backward. Like chipmunks, urban voles had flatter skulls and auditory bullae that were further back. Their auditory bullae have also shrunk as a result of needing to handle the loud, incessant noises of Chicago. While voles' average body size has remained virtually the same, other cranial bones revealed that the creatures have actually been affected by urbanization more than chipmunks. Vole skulls from more urbanized sites were not as diverse in shape as those from regions that were less urbanized, which could mean that the lower variance in closed urban environments keep voles more morphologically similar to each other. It became obvious that chipmunks in urban areas are increasing in size, and their rows of teeth have grown shorter. The researchers think this is because more food is available throughout the year, and that chipmunks having more human interaction has put more things on the menu. Among the free meals chipmunks grab in the city are high-calorie, highly processed foods that add body weight and are easier to chew than nuts (meaning they don't need to use their teeth as much). Urban brown rats have been experiencing the same evolutionary phenomenon. 'As cities continue to sprawl and push outwards, understanding complex morphological responses to increasing urbanization and associated effects can elucidate the impact of human population growth on biota,' the researchers said. '[It can] help us forecast how wild populations will cope with continuing change in the coming decades.' You Might Also Like The Do's and Don'ts of Using Painter's Tape The Best Portable BBQ Grills for Cooking Anywhere Can a Smart Watch Prolong Your Life?
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City living is changing rodent skulls in Chicago
Tiny rodents living in a major American city are unique examples of evolution playing out in real time. Like geologic time itself, the process of evolution itself is generally a very slow process with teeny tiny changes passed down over several generations. All of these small changes eventually result in new adaptations and potentially new species over thousands or millions of years. However, in the face of dramatic shifts in the world around them from climate change to human encroachment, species sometimes must rapidly adapt or die. One of these rapid examples of evolution was hidden away in the drawers of Chicago's Field Museum. While comparing the skulls of common chipmunks and voles found in the Chicagoland area collected over the past 125 years, a team found evidence that these rodents have been adapting to life in an increasingly urban environment. The findings are detailed in a study published June 26 in the journal Integrative and Comparative Biology. 'Museum collections allow you to time travel,' Stephanie Smith, a study co-author and mammalogist at the Field Museum, said in a statement. 'Instead of being limited to studying specimens collected over the course of one project, or one person's lifetime, natural history collections allow you to look at things over a more evolutionarily relevant time scale.' The mammal collections at the museum include over 245,000 specimens from all over the world. Given its location in the Windy City, they have an especially good representation of the animals from Chicago, including raccoons, skunks, a one-in-a-million blue eyed cicada, opossums, robins, and much more. The collections also represent different moments in time throughout the past century. 'We've got things that are over 100 years old, and they're in just as good of shape as things that were collected literally this year,' said Smith. 'We thought, this is a great resource to exploit.' In the new study, the team selected two rodents commonly found in Chicago: eastern chipmunks (Tamias striatus) and eastern meadow voles (Microtus pennsylvanicus). 'We chose these two species because they have different biology, and we thought they might be responding differently to the stresses of urbanization,' added study co-author and Field Museum assistant curator of mammals Anderson Feijósa. Chipmunks are members of the same family as squirrels. The small rodents spend most of their time aboveground, eating seeds, nuts, fruits, insects, and even frogs. Voles, on the other hand, are more closely related to hamsters. They prefer to spend their time in underground burrows and primarily eat plants. [ Related: Squirrels gamble, too—but with their genes. ] Field Museum Women in Science interns and study co-authors Alyssa Stringer and Luna Bian, measured the skulls of 132 chipmunks and 193 voles. Skulls contain important information about an animals' sensory systems and diet, and they tend to be correlated with their overall body size. 'From the skulls, we can tell a little bit about how animals are changing in a lot of different, evolutionary relevant ways—how they're dealing with their environment and how they're taking in information,' said Smith. Stringer and Bian measured different parts of the skulls, noting the overall skull length, the length of the rows of teeth, and other characteristics. They also created 3D scans of the skulls of 82 of the chipmunks and 54 of the voles. This part of the analysis is called geometric morphometrics, and it digitally stacked the skull scans on top of each other so scientists could compare the distances between different, specific points. They found small–but significant–changes in the rodents' skulls over the past 100 years. For the chipmunks, their skulls became larger over time, while the row of teeth along the sides of the mouths shrank. The bony bumps in the voles' skulls that hold the inner ear became smaller over time. However, why the skulls were changing was not immediately clear. To search for the reason behind these skull changes, the team pored over historical records on temperature and levels of urbanization around the Chicagoland area. 'We tried very hard to come up with a way to quantify the spread of urbanization,' says Feijó. 'We took advantage of satellite images showing the amount of area covered by buildings, dating back to 1940.' The specimens collected before 1940 were from two different places: areas that were still wild 85 years ago (so it could safely be assumed that these spots were wild before that) and or from highly urbanized areas like downtown Chicago. Changes in climate didn't explain the alterations in the rodents' skulls, but the degree of urbanization did. The differences in the ways that the skulls changed could be related to the different ways that they were affected by an increasingly urban habitat. 'Over the last century, chipmunks in Chicago have been getting bigger, but their teeth are getting smaller,' said Feijó. 'We believe this is probably associated with the kind of food they're eating. They're probably eating more human-related food, which makes them bigger, but not necessarily healthier. Meanwhile, their teeth are smaller—we think it's because they're eating less hard food, like the nuts and seeds they would normally eat.' By contrast, the voles had smaller auditory bullae–bone structures associated with hearing. 'We think this may relate to the city being loud—having these bones be smaller might help dampen excess environmental noise,' said Smith. While it's clear that these rodents could evolve small changes over time to make it easier to live among humans, the team says that the overarching lesson is not that animals will just adapt to whatever humans can throw at them. Instead, the voles with smaller ear bones and chipmunks with smaller teeth prove just how profoundly human beings affect our environment and how much we can make the world harder for our fellow animals. 'These findings clearly show that interfering with the environment has a detectable effect on wildlife,' said Feijó. 'Change is probably happening under your nose, and you don't see it happening unless you use resources like museum collections,' concluded Smith.
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Sir Francis Graham-Smith, radio astronomy pioneer whose work indicated that the universe had a beginning
Sir Francis Graham-Smith, the former Astronomer Royal, who has died aged 102, was a pioneer of radio astronomy, carrying out research which helped to establish our modern picture of the universe. In the 1950s, he was the first astronomer to measure the accurate positions of distant 'radio galaxies', those that have large regions of radio emission that extend well beyond their visible structure. Together with Sir Martin Ryle, his predecessor as Astronomer Royal, he suggested that the speed at which these galaxies are moving away from us indicated that the universe must have had a definitive beginning. These findings helped to demolish the then fashionable steady state theory of Sir Fred Hoyle and others, which held that the universe had always existed. In the 1970s, Graham-Smith did much detective work on pulsars – fast-spinning stars made up of matter so dense that one ton can be contained in a teaspoon. King Charles II established the office of Astronomer Royal in 1674. Appointed in 1982, Graham-Smith was the 13th to hold the office – an unlucky portent as it turned out, for the 1980s saw a series of cuts in funding for astronomical research. The shadow hanging over British astronomy partly stemmed from a public relations disaster on the night of March 13 1986 when, shortly after midnight, the European spacecraft Giotto passed through the tail of Halley's comet, sending back data to earth. The BBC, in a late-night television show, invited several astronomers, including Graham-Smith to comment on the results, forgetting that none of their guests knew much about comets. The show was a shambles: no one could make head or tail of the Giotto data. But the real row began later in No 10 Downing Street, where Margaret Thatcher was watching the programme. She was angry at what she saw and decided that space research was a waste of money. The next year she barred British participation in a European X-ray telescope searching for black holes and rejected plans to boost the budget of the National Space Centre, a move which prompted the resignation of its director Roy Gibson. Caught in the cross-fire, Graham-Smith strove in as civilised a manner as possible to put the case for higher investment in British astronomical research: 'We have no shortage of excellent students,' he observed in 1986, 'but they will probably work abroad. The fact that we will go on populating the world with British astronomers is absolutely splendid, but wouldn't it be nicer to think that just a few would stay at home?' Francis Graham-Smith was born on April 25 1923 to Claud and Cicely and educated at Epsom College and at Rossall School in Lancashire. He began studying natural sciences at Downing College, Cambridge, in 1941 but did not graduate until 1946. Like his colleague Martin Ryle, he spent most of the Second World War working at the Telecommunications Research Establishment at Malvern involved in the development of radar. This experience led him into radio astronomy and he stayed on at Cambridge after graduating to work with Ryle at the Cavendish Laboratory on radio waves from the sun and other stars. By a fortunate coincidence, the largest sunspot for many years occurred at this time – in July 1946 – and Cambridge radio astronomy grew from observations of its very powerful emissions. Soon afterwards the pair were using the same techniques to detect radio waves coming from other parts of the sky. Setting up a simple radio telescope in a field behind the house where they both lived, they left it for 24 hours to scan the sky as the earth rotated recording the radio signal on a paper chart recorder. When they looked at the chart the next morning, they were astonished to see the trace of not one but two powerful radio sources on the recording. The radio source appeared to be coming from the constellation Cassiopeia. A few years later, the radio source was precisely located and identified with the remains of a stellar explosion in the Milky Way. Another target of their research was a radio signal coming from a discrete source in the constellation of Cygnus. In 1952, Graham-Smith located this radio signal known as the galaxy Cygnus A (the 'A' indicating that it is the brightest light in its constellation), sufficiently accurately for a visual search to be made for a visible counterpart. This search turned out to be a turning point in modern astronomy. American researchers using large optical telescopes found that the radio waves were coming from a galaxy of unusual shape and with a large 'redshift' – evidence that it is moving away from earth at a speed which increases with distance. This discovery demonstrated that radio astronomy could be used for penetrating great distances outside our own galaxy. Cygnus A is the first known example of a radio galaxy. In 1952 Graham-Smith went to America to work at the Carnegie Institute in Washington, returning to Cambridge in 1953. He published a paper with Ryle in 1957 suggesting that radio signals from orbiting satellites could be used to aid navigation. Throughout the 1960s and 1970s Graham-Smith worked on radio astronomy at Jodrell Bank, then moved into optical astronomy as director of the Royal Greenwich Observatory, where his main task was to build the new optical telescope at La Palma in the Canary Islands. In 1977 he was part of a team working at the British-American optical telescope in New South Wales which photographed the Vela Pulsar, the brightest pulsar in the sky in terms of radio emissions, no more than 30 miles in diameter yet weighing one and a half times as much as the sun. The star's total explosion or 'supernova' had been recorded in Sumerian inscriptions. In 1981 Graham-Smith moved back to Manchester to become only the second director of Jodrell Bank – where he had a cameo in the series Treasure Hunt, giving Anneka Rice a piggy-back to help her reach a clue. He listed bee-keeping among his recreations in Who's Who, and looked after the hives at Jodrell Bank. In 1982 he was appointed Astronomer Royal, and he was professor of physics at Manchester from 1987 to 1990. After his retirement, Graham-Smith – who was known as Graham to friends and colleagues – became vice-president of the Royal Society and his attention turned increasingly to the future of our own planet. In 1994 he hosted an international population summit which concluded that zero population growth 'within the lifetime of our children' was the only way to save the earth from ecological disaster. He was knighted in 1986 and elected a Fellow of the Royal Society in 1970. He married, in 1945, Dorothy Palmer, whom he met when they were both working on radio astronomy with Martin Ryle in Cambridge; they had a daughter and three sons. Professor Sir Francis Graham-Smith, born April 25 1923, died June 20 2025 Broaden your horizons with award-winning British journalism. Try The Telegraph free for 1 month with unlimited access to our award-winning website, exclusive app, money-saving offers and more.
