List of mammals of Connecticut

This list of mammals of Connecticut includes both native and nonnative species (introduced or invasive) found in the U.S. state of Connecticut now or in the past, but not domesticated or farm animals.
Many mammals formerly extirpated in the state have returned, sometimes with active human projects and sometimes through a natural expansion from neighboring states as Connecticut's natural environment has become more welcoming to them.
Many mammal species were removed from Connecticut or almost became extinct within the state through hunting and clearing forests to create farmland, starting in the 17th century with European colonization and continuing until the 19th century, when most of the state's forest covering had been replaced with farmland. Populations of moose, turkeys, black bears and mountain lions lost their habitats and were greatly reduced or eliminated in Connecticut. Pollution in the 19th and 20th centuries also played a role in either greatly reducing or extirpating some species, such as the bald eagle.
With the collapse of farming in the 19th century and its continued decline in the state in the 20th century, forests spread back over much of the land. They are not the same forests, however: Chestnut trees, for instance, wiped out by a disease, are not nearly as prevalent as they once were, and the lack of their nuts affects the populations of various mammals. Stone walls, built largely in the 19th century, provide more welcoming homes to certain species; and mammals from Europe, including the house mouse and Norway rat, and from elsewhere (such as the coyote) can create a different competitive environment for some species and a different food source for some (the barn owl, for instance, can now feed on Norway rats).
To some extent, deforestation and fragmentation of forests has occurred in recent decades with expanded residential development. Some improvements have come with the removal of certain industries from Connecticut since the mid-20th century and the installation of more sewage treatment plants and improvements in their functioning. Residual industrial pollution remains, however, and prevailing winds keep Connecticut on the receiving end of pollution from the New York City metropolitan area and other areas south and west of the state, Connecticut also continues to produce some of its own pollution.
Dead animals killed by cars on the state's roads are one of the primary ways state residents see diverse varieties of local mammals. The more common roadkill in Connecticut consists of striped skunks, opossums, raccoons, and gray squirrels.
Species.
Opossums (Order Didelphimorphia, Family Didelphidae)
Shrews and moles.
Shrews (Order Eulipotyphla, Family Soricidae)
Moles (Order Eulipotyphla, Family Talpidae)
Bats.
Bats (Order Chiroptera, Family Vespertilionidae)
The state has eight extant species of bats, plus at least one which may now be extirpated from the state.
Because some bats have rabies, the state Department of Environmental Protection (now DEEP) advises on its Web site: 
Bats that occupy buildings:
Bats that roost in trees in summer:
Bats that hibernate in caves and tunnels:
Rabbits and hares.
Rabbits and hares (Order Lagomorpha, Family Leporidae)
Rodents.
Squirrel family (Order Rodentia, Family Sciuridae)
Beavers (Order Rodentia, Family Castoridae)
Mice, rats, voles, lemmings (Order Rodentia, Family Muridae)
Jumping mice (Order Rodentia, Family Dipodidae, Subfamily Zapodinae)
New World porcupines (Order Rodentia, Family Erethizontidae)
Hoofed mammals.
Deer (Order Artiodactyla, Family Cervidae)
White-tailed deer.
White-tailed deer ("Odocoileus virginianus") — The population in the state is enormous and growing in large part because of the expansion of rural residential lands that are hospitable for deer but not suitable for hunting. Other factors are the mixture of young and mature forests, milder winters, and fewer predators. Deer were nearly eliminated from the state by the end of the 19th century, with fewer than 20 in all of Connecticut, although they were on the rebound by that point, in part due to state regulations to protect them. In 1907 the state allowed landowners to shoot deer causing crop damage. In 1974, the state passed its first deer management act and regular, licensed deer hunting began the next year. By the 1970s, the total state population was about 20,000, and up to 76,000 (a low estimate) in 2000.
Fairfield County has the highest deer density in the state. According to one estimate, the county has 59 per square mile, more than double the density in the rest of the state, according to the state Department of Environmental Protection. But another estimate, based on a survey in the winter of 2006–2007 estimated only 29.4 deer per square mile in the county. Deer can carry up to 1,000 ticks, many of which have Lyme disease. The state allows bowhunting for deers from September 15 to January 31. (According to an estimate in "Connecticut Wildlife", published in 2004, "Winter density ranges up to about 40 per square mile in southwestern Connecticut, with a statewide mean of 21 per square mile.")
Connecticut has several problems associated with its large deer population:
Moose.
Moose ("Alces alces") — have become more prevalent in Connecticut in recent years, with the first documented reproduction (a female and two calves) found in 2000, and an estimated 100 in the state as of 2007. As of 2015, they come from Massachusetts whose population is rising dramatically over 1000, the population could be over 200 Most of these moose now live in northern Litchfield County, especially the towns of Hartland, Colebrook and Granby. They can occasionally be found throughout northern Litchfield and northwestern Hartford Counties and are known to wander throughout the state. When forests were largely replaced by farmland in the seventeenth through nineteenth centuries, populations of moose (along with animals such as turkeys, black bears and mountain lions) lost their habitats and were greatly reduced or eliminated from the state. But even before Connecticut was settled by Europeans, the moose population was never large, according to the DEP. Moose are thought to be entering the state from the north (but have roamed as far south as Stamford and Fairfield, communities on Long Island Sound). In Massachusetts, three or four moose are hit by trains each year and about 15 motor vehicle collisions with the animals occur, although in some years there have been as many as 50. One Massachusetts environmental official estimated there were about 1000 moose in Massachusetts.
The greatest danger to people from moose is car collisions. From 1995 to 2006, there was an average of one collision a year of a moose and an automobile across the state, although in the first half of 2007, there were four, including one in June on the Merritt Parkway in Stamford. Unlike deer, moose that feel threatened tend to stand their ground.
Local police are authorized to kill the animals if they pose a threat to public safety, which in practice almost only means that the animal is getting too close to a highway. In 2007, police killed bull moose in separate incidents in Waterbury and Fairfield when each moose came close to a highway. In cases where no threat to the public seems imminent, DEP officials will usually try to tranquilize the animal or harass them into a nearby woods (sometimes by banging on pots or forming a line to try to scare the animal away). In 2008, state authorities knocked out a year-old female moose in New Britain with a tranquilizer dart and released it on state forest land in northern Connecticut. Moose are generally reclusive, but male moose tend to wander about in the fall, during their mating season, and year-old moose tend to wander when their mothers get ready to give birth to new calves, according to the state Department of Environmental Protection. The 2008 New Britain moose, for example, was thought by officials to be the same animal seen in Avon and Farmington the week before.
Elk.
Eastern elk ("Cervus canadensis canadensis") — extinct. Elk are extirpated from the state.
Mammals in Long Island Sound.
"For more information on mammals in Long Island sound, see Long Island Sound."
Whales (Order Cetacea, Family Delphinidae)
Porpoises (Order Cetacea, Family Phocoenidae)
Seals (Order Carnivora, Family Phocidae)