Eastern gray squirrels can be black or gray, and new research reveals how surprisingly local conditions are linked to their coat color.<\/p>\n
A black squirrel in a city park may seem like a small detail. But its coat color can reveal something bigger about how animals live in cities.<\/p>\n
Cities change nature<\/a> in many ways. Buildings trap heat, trees disappear in some areas, and rivers can separate animal populations that live only a short distance apart.<\/p>\n New work on eastern gray squirrels in Montreal shows that these local differences matter. <\/p>\n Black squirrels were much more common in some parts of the region than others, and the pattern was most strongly linked to winter temperature, tree cover, and geography.<\/p>\n For people, the finding offers a simple lesson about urban wildlife<\/a>. A city is not one environment, and animals living in different neighborhoods may face very different conditions.<\/p>\n Why squirrel color tells a bigger story<\/p>\n Eastern gray squirrels do not always have gray fur. Some are dark brown or black because of a known genetic change that affects coat color.<\/p>\n This darker form is called melanism. Because coat color is easy to see, squirrels give researchers a useful way to track how a visible trait changes across one metropolitan area.<\/p>\n Francis Quang-Hai Dinh, the paper\u2019s first author from McGill University<\/a>, collected observations across Montreal.<\/p>\n \u201cI visited almost 200 parks around the city on my bicycle during my free time the first summer that I was at McGill, and observed over 800 squirrels, some of whom were gray and others were black,\u201d Quang-Hai Dinh said.<\/p>\n Tracking squirrels across Montreal<\/p>\n The published analysis included surveys from 197 parks, along with public observations from iNaturalist<\/a> and SquirrelMapper<\/a>. <\/p>\n Altogether, the researchers analyzed 1,734 squirrel observations from across the Montreal metropolitan area.<\/p>\n About 12.8% of the squirrels were black or very dark. That citywide average hid major differences from one part of Montreal to another.<\/p>\n Near the city center, black squirrels made up only about 5% of the animals recorded. Their numbers rose strongly toward the north and west, but not toward the south and east.<\/p>\n In northern rural areas, about 58% of squirrels were melanic, while the figure was about 37% in western areas. Some southern and eastern areas stayed close to 5%.<\/p>\n Colder and greener places stood out<\/p>\n The team compared squirrel color with features of the parks, including winter temperature, tree canopy, park size, roads, buildings, paved surfaces, and distance from downtown.<\/p>\n Two features stood out most clearly: colder winter temperatures and greater tree cover. Black squirrels were more common in places that had both.<\/p>\n A dark coat can help squirrels hold onto heat in cold weather, which could help explain why black squirrels remain common in colder areas.<\/p>\n The researchers did not measure body temperature, survival, or reproduction, so they cannot say that cold weather caused more black squirrels to survive.<\/p>\n Tree cover may also matter because animals with different coat colors can be easier or harder to see against different backgrounds. <\/p>\n The analysis found a connection, not proof that trees directly determine which coat color does better.<\/p>\n Urbanization was not the whole answer<\/p>\n Urbanization itself was not the strongest predictor of squirrel color. More urbanized areas tended to have warmer winters and less tree cover.<\/p>\n Those local conditions were more closely linked with melanism than the broad measure of urban development. <\/p>\n This suggests that city life may matter partly because development changes the conditions animals<\/a> experience.<\/p>\n Two parts of the same city can therefore be very different for wildlife. One area may be warmer and heavily built, while another may have more trees and colder winters.<\/p>\n Looking only at \u201curban\u201d and \u201crural\u201d can miss the smaller environmental differences that animals actually experience.<\/p>\n Rivers may keep populations apart<\/p>\n Montreal is divided by major waterways, including the St. Lawrence River and its tributaries. <\/p>\n The researchers found sharp changes in the proportion of black squirrels between some regions separated by these waterways.<\/p>\n Professor Allison Roth, the paper\u2019s senior author, is now at the University of Missouri<\/a>.<\/p>\n \u201cPeople often think of cities as a single type of environment, but our findings show that the conditions animals experience can vary dramatically from one neighborhood to another,\u201d Professor Roth said.<\/p>\n \u201cThese local differences, along with barriers such as rivers, can shape how wildlife populations evolve, which means we need to look beyond simple urban-rural comparisons to understand adaptation in cities.\u201d<\/p>\n Large rivers could make it harder for squirrels from different areas to mix. Over time, that could help keep coat-color differences between populations on opposite sides.<\/p>\n The team did not track squirrels crossing rivers or collect genetic samples for this project. The idea that rivers limit movement is therefore a possible explanation, not something this work proved.<\/p>\n Limitations of the study<\/p>\n The results do not prove that Montreal\u2019s squirrels are evolving right now. <\/p>\n The researchers mapped where coat colors occur, but they did not measure whether black or gray squirrels survive longer or produce more offspring.<\/p>\n Their field surveys focused on parks, so squirrels living around houses, streets, or commercial areas may experience different conditions. <\/p>\n The surveys also took place during the middle of the day, when squirrel activity<\/a> can be lower.<\/p>\n Coat color can also affect how easy an animal is to notice. <\/p>\n Dark squirrels may be harder to see in shaded places, while people using citizen science apps may be more likely to photograph a black squirrel because it looks unusual.<\/p>\n The three datasets showed broadly similar coat-color patterns, but the researchers could not completely rule out these possible biases.<\/p>\n Why local differences matter<\/p>\n The larger message goes beyond the color of Montreal\u2019s squirrels. Animals<\/a> living in one city do not all experience the same heat, tree cover, barriers, or access to surrounding habitat.<\/p>\n \u201cThis project shows how discoveries can be accessible and that you can do science in your backyard,\u201d Francis Quang-Hai Dinh said.<\/p>\n That makes familiar urban animals useful for understanding how human-built landscapes interact with nature<\/a>. <\/p>\n A change visible in squirrel fur can reveal environmental differences that broad citywide labels may miss.<\/p>\n The findings do not show that one type of city environment always favors black or gray squirrels. <\/p>\n Instead, they show that local conditions and geography are both linked with where the different coat colors occur.<\/p>\n The study is published in the Journal of Animal Ecology<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? 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