Do you want to learn about the mammals that live in Pennsylvania?
Luckily, you’ve come to the right place!
I have compiled a list of the most common and interesting mammals in Pennsylvania, with photos, facts, and RANGE MAPS. As you will see, there are lots of species, each with different and interesting habits and traits.
Here are 33 types of MAMMALS found in Pennsylvania!
#1. American Black Bear
- Ursus americanus
- Adults range from 5 to 6 feet tall and weigh 200 to 600 pounds.
- Coloration ranges from mostly black on the east coast to brown, cinnamon, or blonde in the west, and blue-gray or even creamy white in some populations.
- They have a flat back, small head, rounded ears, and non-retractable claws.
American Black Bears occupy various habitats in Pennsylvania but generally prefer inaccessible terrain.
Black bears are sometimes considered a nuisance because they sometimes damage cornfields, honeybee hives, and berry farms. In addition, they’re easily attracted to garbage, bird feeders, and coolers. Make sure to NEVER feed them, as this can make the bear not afraid of humans, which is dangerous for both people AND the bear.
Generally, Black Bears are timid around people. Unlike grizzly bears, females with cubs rarely attack people, often just sending their cubs up a tree so that they can retreat safely.
Black Bears are naturally active in the evening and early morning but sometimes alter their activity patterns for food availability. Bears may become active during the day when garbage and other human food sources are available. Black Bears in campgrounds often develop nocturnal activity patterns.
Despite the common belief, Black Bears in Pennsylvania don’t truly hibernate.
Instead, they enter a state of shallow torpor. In this state, their body temperature decreases, their metabolism slows, and they don’t need to wake to eat, drink, urinate, or defecate. Consequently, Black Bears must put on a heavy layer of fat in the fall to survive through winter and spring.
- Cervus canadensis
- Adults stand 4.5 to 5 feet tall at the shoulder and weigh between 400 and 800 pounds.
- Their coloring is light brown with a dark brown shaggy mane from neck to chest in winter and reddish-brown in summer.
- They have thick bodies, short tails, and long legs, and bull (male) Elk grow massive antlers yearly.
The Elk is one of the largest mammals in Pennsylvania.
They can be found in deciduous woodlands, boreal forests, mountainous areas, and grasslands. Most populations migrate seasonally. During the spring, they follow the retreating snow, traveling to higher elevations to graze. In the fall, they return to lower elevations and wooded areas that afford greater food availability.
Elk are herbivores that consume an average of 20 pounds of plant material per day! Elk are ruminants, meaning they have four-chambered stomachs. This trait allows them to eat quickly and then move to more sheltered areas to digest their food.
This species is one of the most gregarious members of the deer family and forms herds of up to 400 individuals. The herds are separated into small male groups and larger female groups. Female Elk sometimes produce an alarm bark to warn herd mates of danger. Conversely, males produce a high-pitched, bugling call during the rut to signal their availability and fitness to females.
#3. White-Tailed Deer
- Odocoileus virginianus
- Adults range from 63 to 87 inches long and stand between 31 and 39 inches tall at the shoulder.
- Their coloring is tan or brown during the summer and grayish in winter, with white on the throat, chest, and underside of the tail.
- The males have antlers which they shed in the winter.
The White-tailed Deer is the most numerous large mammal in Pennsylvania!
White-tailed deer have an extensive range in North America and are able to thrive in various habitats, including coniferous, mixed, and deciduous forests, sawgrass and hammock swamps, cactus and thorn brush deserts, brushy areas, and farmlands. You’re most likely to see White-tailed Deer around dawn and dusk when they forage.
They are also completely comfortable in suburban environments, and it’s common for them to live in small wooded parks near housing developments. The herd in my neighborhood is particularly fond of our bird feeders. They stop by for a snack almost every evening!
There aren’t many things cuter than a baby deer! The fawns are born with white spots and are able to walk almost right away. The does may leave the fawns to forage for hours at a time. While their mother is away, the fawns lay flat on the ground with their necks outstretched and are well camouflaged. The female deer always come back to the baby, so make sure not to disturb the fawn if you find one!
#4. Wild Boar
- Sus scrofa
- Adults range from 5 to 8 feet in length and weigh between 145 and 600 pounds.
- Their thick, coarse hair ranges in color from black to reddish-brown.
- They have large heads and necks and relatively short legs. Males have long bristly hairs down the middle of their back and large canines that protrude from the mouths of adult males.
Wild Boars occupy various habitats but prefer areas with water sources and some dense vegetation for shelter. They generally don’t thrive in habitats with extreme heat or cold.
Wild Boars are omnivores and what they eat varies with season and location. They consume large amounts of plant matter, including fruits, nuts, roots, herbaceous plants, and crops. They’re also known to eat bird eggs, carrion, small rodents, insects, and worms. Their voracious appetite can be very detrimental to an ecosystem, causing a loss of plant diversity and extensive soil erosion.
Wild Boars are invasive mammals in Pennsylvania, as they were introduced from overseas. Their population has exploded in the last 50-100 years, leading wildlife departments to put population control programs in place.
- Lynx rufus
- Adults weigh 15 to 35 pounds, stand 18 to 24 inches tall, and measure 28 to 47 inches in length.
- Their coloring is buff to brown, sometimes with a reddish tint, and black and brown spots and stripes.
- They have facial ruffs, ear tufts, white spots, and short, bobbed tails.
Bobcats are solitary, elusive, and shy mammals that are rarely seen in Pennsylvania.
These cats are highly adaptable and found in various habitats. They may be seen in residential areas. However, they generally avoid extensively cleared agricultural lands.
As carnivores, Bobcats are highly skilled hunters. They can climb, run up to 30 miles per hour, and leap high enough to grab low-flying birds. They patiently stalk their prey until they are close enough to pounce.
The largest threat to Bobcat populations is habitat fragmentation due to their large home ranges and elusive nature. However, rodenticides can also cause issues in populations when they feed on contaminated prey.
#6. Red Fox
- Vulpes vulpes
- Adults range from 18 to 35 inches in length and weigh 7 to 31 pounds.
- Their coloring ranges from pale orange or red to deep reddish-brown on their upper parts with white on their underside.
- They have black feet, a fluffy white-tipped tail, and large, pointy, black-tipped ears.
Red Foxes are arguably the most beautiful mammal in Pennsylvania!
These canines are often thought of as cunning and smart, with good reason! They’re excellent hunters and foragers. They also cache food and are adept at relocating it. Although they prefer rabbits, fish, and berries, they won’t hesitate to eat anything readily available.
This species has a distinctive way of hunting mice and other small rodents. Once the prey has been detected, they stand motionless, waiting and listening. Then they leap high into the air and bring their forelegs straight down, pinning the rodent.
Once baby foxes, known as kits, reach adulthood, their biggest threat is humans, who hunt and trap them for fur or kill them to protect livestock, such as chickens. Red Foxes can live 10 to 12 years in captivity but average only about three years in the wild.
#7. Gray Fox
- Urocyon cinereoargenteus
- Adults range from 31.5 to 44.3 inches long and stand 12 to 16 inches tall.
- Their fur is peppery gray on top and reddish brown everywhere else.
- They have a pointed muzzle and ears, long hooked claws, and a bushy tail with a black stripe on top.
Gray Foxes live in deciduous forests in Pennsylvania with a mix of brushy and woodland areas. They occasionally visit agricultural lands, but not as frequently as Red Foxes. Gray Foxes also prefer habitats with access to water, so you’re more likely to see them near rivers or lakes.
You’ll have a tough time finding this species, since they are primarily nocturnal and incredibly skittish of people. During the winter breeding season from December through March, they socialize with their mates but spend little time with other foxes.
Females give birth to litters of one to seven pups in the den, and the fathers provide most of their food after they are weaned. Males teach their pups hunting skills by practicing pouncing and stalking, and they begin to hunt at around four months of age.
- Canis latrans
- Adults range in length from 3 to 4.5 feet and weigh between 15 and 44 pounds.
- Their coloring is grayish to yellow-brown on top with white underparts.
- They have a bushy tail, large, triangular ears, narrow muzzle, black nose, and yellow eyes.
Coyotes have a large range in North America and are found in various habitats, from the tropics to the tundra. Coyotes expanded their range after the near extermination of wolves and cougars by European settlers.
As with habitat, coyotes are highly versatile in their food selection. Despite being primarily carnivorous, they consume various plants, including berries, grass, and food crops. They will eat almost anything, and this extensive menu allows them to thrive in nearly every environment in Pennsylvania!
Even if you haven’t seen one, you’ve probably heard a Coyote before! They’re extremely vocal and communicate through howls, yips, whines, and barks. These vocalizations are used to warn pack mates of danger, greet each other, and play.
Sadly, Coyotes are commonly hunted and trapped for fur and sport.
#9. Snow Shoe Hare
- Lepus americanus
- Adults range from 16.4 to 20.4 inches in length.
- In summer, the fur is a rusty grayish brown with a dark line down the middle of the back.
- In winter, the fur is almost entirely white except for black eyelids and blackened tips of the ears.
Snowshoe Hares are perfectly adapted to cold, snowy areas of boreal and coniferous forests. They get their name from the thick fur and large toes on their back feet, which allow them to run across the snow without sinking in. In warmer climates, Snowshoe Hares are found only in the mountains where the weather is cooler and snowy.
You’re most likely to spot this mammal in Pennsylvania at dawn or after dusk. Snowshoe Hares are primarily herbivorous and consume various plants depending on the season. In summer, they feed on grasses and wildflowers. Then, they switch to buds, twigs, and bark from conifer trees in winter.
About 85% of leverets (baby hares) won’t make it through their first year of life. Those that do survive live up to five years in the wild. They have many predators, including squirrels who eat the young, Lynx, bobcats, mink, wolves, coyotes, and foxes. Unlike rabbits that freeze when threatened, Snowshoe Hares often rely on their speed to escape to cover.
Snowshoe Hare populations are believed to be currently stable. However, researchers believe they face a unique threat from climate change. Regardless if there is snow or not, they continue to turn white in the winter, putting them at an increased risk for predation if they are not blending into their surroundings.
#10. Eastern Cottontail
- Sylvilagus floridanus
- Adults are about 16.5 inches long and weigh up to 3 pounds.
- Their coloring is reddish-brown on the upper body with white on the underparts and tail.
- They have distinctive, large eyes and a round, fluffy tail.
These small mammals are vulnerable to many predators in Pennsylvania, so they require a habitat with good cover. Areas with a mix of grasses, dense shrub thickets, blackberry bushes, and brush piles are ideal. Well-drained fields with dense grass cover are often used for nesting.
One of their favorite places to nest is suburban yards! So, if you notice Eastern Cottontails hanging around your property, be careful when you mow your lawn. Although rabbit nests are usually slightly below ground level, lawn equipment is still dangerous for baby rabbits and mothers.
Eastern Cottontails consume a wide range of plant materials. They can be a nuisance for gardeners by eating garden plants and flowers. However, in winter, they eat woody materials from birch, oak, dogwood, sumac, and maple trees.
If threatened, Eastern Cottontails either freeze or flush. When they flush, they will run to cover in a zig-zag pattern reaching speeds up to 18 miles per hour. If grabbed, they may give a loud distress cry to startle a predator into releasing them.
#11. Striped Skunk
- Mephitis mephitis
- Adults range from 18 to 32 inches long.
- Their coloring is black with two thick white stripes running down the back and tail and a thin white stripe from snout to forehead.
- They have a bushy black tail, small triangular heads, short ears, and black eyes.
Striped Skunks have perhaps the worst reputation of any mammal in Pennsylvania.
They’re best known for their unusual defense system. When threatened, a Striped Skunk will first stomp its feet or handstand as a warning. If these aren’t heeded, the skunk bends its hindquarters to face the animal and releases its defensive smelly spray. The unpleasant, oily liquid can reach up to 20 feet and may cause nausea, intense pain, and temporary blindness.
Despite their foul odor, Striped Skunks provide benefits to humans in the form of pest control. In the summer, they’re largely insectivorous and feed heavily on grasshoppers, crickets, beetles, and bees. The best thing to do if you see a skunk is to give it space. They usually move on quickly when they notice humans!
Striped Skunks have stable and abundant populations. However, some local populations have been affected by rabies outbreaks. In addition, Striped Skunks face threats from severe weather, chemical exposure, and vehicle collisions.
These small mammals are typically very common in suburban areas but are rarely seen because they are nocturnal. As seen below, they often visit bird feeders to eat leftover seeds on the ground!
#12. Eastern Spotted Skunk
- Spilogale putorius
- Adults are 14 to 24 inches long.
- They have long, soft, glossy, black fur with white spots and stripes on the ears and back.
- They have a small head, short legs, and a prominent, black, long-haired tail.
Eastern Spotted Skunks are found in various open habitats, including mature forests that provide adequate cover. They may also occupy agricultural areas and use buildings, corn cribs, rock piles, haystacks, and other debris for cover and den sites.
Although their preferred food during summer is insects, Eastern Spotted Skunks are omnivores. During the fall and winter, they feed on equal amounts of plant and animal matter. They consume bees and wasps, larvae, and honey. They will also eat other insects, eggs, and small animals.
When threatened, Eastern Spotted Skunks will often assume a defensive posture in which they do a handstand on their front legs with their tail straight up and back legs spread apart in the air. They can balance and move forward in this stance while aiming specialized glands at the predator. If this display doesn’t work, then they spray a smelly deterrent.
The population of these small mammals is believed to have declined by more than 90% in Pennsylvania since the 1940s. As a result, they are listed as vulnerable on the IUCN Red List of Endangered Species. Contributing factors include unregulated over-hunting and trapping, habitat loss and fragmentation, widespread pesticide use, increased pressure from predators, and disease.
- Procyon lotor
- Adults are about 3 feet long and weigh between 15 and 40 pounds, though some males grow to over 60 pounds.
- Their fur is grayish-brown with 4 to 6 black rings on the tail and a black “mask” marking around the eyes.
- They have bushy tails and paws with five long, finger-like toes.
These mammals are one of the most common in Pennsylvania!
Due to their ability to adapt to humans, Raccoons have an extensive range and are found in forests, wetlands, suburbs, parks, and cities. They generally avoid large open areas and thrive in areas with water sources, abundant food, and den sites. They make dens in rock crevices, hollow trees or logs, burrows, caves, mines, old buildings, rain sewers, or other cavities for winter shelter and birth.
As opportunistic omnivores, Raccoons will eat both plant material and animals. They feed on practically anything they can fit in their mouths. Interestingly, in areas where food is abundant individual raccoons have been known to develop specific food preferences. Raccoons in urban locations are often larger than those in unpopulated areas because they have adapted to live on human hand-outs, pet food, and trash. They also generally have the benefit of fewer predators.
The second part of the Raccoon’s Latin name, “lotor,” translates to “washer,” referring to a unique behavior they exhibit. They often pick up food items and rub them with their paws, sometimes removing unwanted parts. This gives the appearance that they’re washing their food.
Lastly, they have REALLY cute babies. 🙂
#14. Groundhog (Woodchuck)
- Marmota monax
- Adults measure between 16.3 and 26.6 inches long.
- Their coloring ranges from gray to cinnamon to dark brown, and they have white-tipped guard hairs, which give them a silvery appearance.
- They are stocky, with rounded ears and a bushy tail.
Groundhogs, also called Woodchucks or whistle pigs, occupy forests, fields, pastures, and hedgerows. They thrive near humans, and agriculture operations have increased their food access. Groundhogs construct dens; most have a summer den near food sources and a winter den near protective cover.
In the fall, Groundhogs store large amounts of fat for hibernation. They are “true hibernators,” meaning that their body goes dormant for the entire season. During this time, their heart rate and body temperature fall dramatically until they leave hibernation in late winter or early spring.
Unfortunately, these mammals can become a nuisance in Pennsylvania to farmers, gardeners, and homeowners due to their tunneling behavior. Groundhogs are most affected by vehicle collisions, hunting, trapping, and predation from various species, including domestic dogs.
#15. River Otter
- Lontra canadensis
- Adults grow 3 to 4 feet in length, including their tails.
- Their thick, protective fur is dark brown on the body and lighter brown on the belly and face.
- They have short legs with webbed feet, a long narrow body, and a long, muscular tail.
North American River Otters are semi-aquatic mammals that have an extensive range. They’re found in lakes, rivers, marshes, and estuaries in cold and warm climates. River Otters create dens along the shore that have entrances underwater. They forage at night but can be seen at all times of the day.
River Otters are lively, playful animals and are sometimes even spotted sliding around in the mud or snow. These activities help them to form social bonds and practice hunting techniques.
They use their long whiskers to detect prey in dark water, often grabbing a meal before the victim knows what’s happening. River otters are excellent swimmers, divers, and quick runners. They can stay underwater for up to eight minutes and run 18 miles per hour.
During the 19th and 20th centuries, river otters were heavily trapped and hunted for their fur to near extinction. Conservation and reintroduction efforts are helping many populations to recover; however, some northern populations are still considered vulnerable or imperiled. River Otters continue to face threats from water pollution and habitat destruction.
#16. Common Muskrat
- Ondatra zibethicus
- Adults range from 16 to 25 inches in total length and weigh 1.5 to 4 pounds.
- Their coloring is blackish-brown on the back, lighter brown with a reddish tinge on the sides, and pale on the underside.
- They have short front legs with small feet, strong hind legs with large, partially-webbed feet, and a vertically flattened, scaly tail.
Muskrats are one of just a few semi-aquatic mammals in Pennsylvania.
They occupy marshes, streams, ponds, rivers, and lakes with fresh and brackish water. This species lives in dens built into riverbanks or lodges they construct from sticks. Muskrats construct homes with underwater tunnels and dry, above-water chambers. Interestingly, they will sometimes move into occupied beaver lodges and cohabitate with them.
Being mostly omnivores, Muskrats typically feed on aquatic plants such as cattails, water lilies, and duckweeds. But when food is scarce, they sometimes eat other animals, including crayfish, snails, frogs, insects, and fish.
Muskrats are an important part of the ecosystem in Pennsylvania, helping keep areas of marshes open and creating essential habitats for waterfowl. Unfortunately, this species was introduced to Europe as fur stock and has become invasive in many countries. They cause issues by burrowing into dikes and levees and causing flooding.
#17. Eastern Gray Squirrel
- Sciurus carolinensis
- Adults are 16.6 – 21.6 inches (42 – 55 cm) long.
- Their coloring is gray-brown on the back and sides, with a white belly.
- This species has an extremely bushy tail, pointed ears, and a narrow face.
Many people battle with these small mammals in Pennsylvania at their bird feeders!
Eastern Gray Squirrels eat various foods, but naturally, their favorites are nuts, such as acorns, walnuts, and hazelnuts. As winter approaches, Eastern Gray Squirrels start hiding food in many locations, which provides them nutrition through the colder months. They hide more food than they will ever find, and some extra seeds will eventually grow into new trees. Who knew that squirrels could play such an important role in seed dispersal?
Eastern Gray Squirrel Range Map
Many people have thrown up their hands in defeat as they try to stop these acrobatic mammals from taking over the bird feeders in their backyard. Eastern Gray Squirrels LOVE birdseed and are relentless when they know an easy meal awaits inside a feeder. Their favorite foods include sunflower seeds, peanuts, and corn.
Some gray squirrels are black! Yes, I realize it’s strange that some Eastern Gray Squirrels have black fur, but it’s true! These black squirrels appear as a morph, and genetically speaking, it’s believed to result from a faulty pigment gene. No one is sure why the black morph evolved, but several theories have been offered. For example, some scientists think it may be a selective advantage for squirrels that inhabit the northern ranges to help them absorb heat.
- RELATED: Watch my LIVE animal cameras on Youtube! (You may see an Eastern Gray Squirrel right now in my backyard)
#18. American Red Squirrel
- Tamiasciurus hudsonicus
- Adults are 11- 14 inches (28 – 35.5 cm) long.
- Their coloring is reddish-brown with a white belly.
- These tiny squirrels have inquisitive-looking faces with bright white rings around their eyes.
The American Red Squirrel is easy to identify compared to other squirrel species. As the name suggests, they have a reddish color and white belly that makes them easy to distinguish. Size-wise, they are both MUCH smaller than both gray and fox squirrels but larger than chipmunks.
American Red Squirrel Range Map
These small mammals are primarily found in Pennsylvania in coniferous forests due to their diet, which consists of seeds from evergreen trees. But they are equally at home in deciduous forests, backyards, parks, and urban areas, where they adjust their diet to eat foods such as berries, bird eggs, acorns, hazelnuts, mushrooms, mice, and sunflower seeds from backyard bird feeding stations. American Red Squirrels even have a sweet tooth and are known to tap maple trees so they can eat the sugar from the sap!
These squirrels are BEST known for their aggressive personality!
Press PLAY to hear the sounds of an American Red Squirrel!
When I go hiking, I almost always see at least one American Red Squirrel, as they are not shy creatures. As soon as I’m spotted, the squirrel typically runs up a tree to sit and starts making loud chattering noises to alert the whole forest to my presence!
#19. Fox Squirrel
- Sciurus niger
- Adults are 17.7 – 27.6 inches (45 – 70 cm) long.
- They have gray-brown fur on the back and orange bellies.
- This species has bushy tails, rounded ears, and large black eyes.
Fox Squirrels are the largest tree squirrel in Pennsylvania.
These small mammals can adapt to many different habitats in Pennsylvania. However, they are most often found in small patches of deciduous forests that include trees that produce their favorite foods, which are acorns, walnuts, pecans, and hickory nuts. To prepare for winter, they hide caches of these nuts all over the place to be eaten later when the weather turns cold.
In addition, Fox Squirrels thrive living around people. Consequently, they are commonly found in urban parks and neighborhoods.
Fox Squirrel Range Map
You will likely see Fox Squirrels foraging on the ground, as they spend much of their time there. But don’t let this fact fool you since they are still skilled climbers. In addition to scaling trees, they will easily climb a bird feeder pole to access birdseed. 🙂
#20. Eastern Chipmunk
- Tamias striatus
- Adults average about 9.6 inches, including their tail.
- They are reddish-brown on the back and white on the undersides, with two white stripes on each side and one black stripe down the middle of the back.
- They have pouched cheeks for carrying food, prominent eyes, and rounded ears.
These vocal animals got their name from the “chip-chip” sound they make. Despite their small size, Eastern Chipmunks construct burrows of interconnecting tunnels between 12 and 30 feet long! The burrows have many chambers that provide shelter from predators, a place to birth young, and a place to store food they cache for winter.
Being mostly omnivorous, Chipmunks primarily eat nuts, seeds, acorns, mushrooms, and fruit. However, they may also eat insects, snails, bird eggs, and small mammals like young mice.
Chipmunks are diurnal, meaning they sleep in their burrow at night and spend the day foraging and catching food. You’re most likely to see them during early fall when they cache as much food as possible for winter. They spend the winter in their burrow, often in deep sleep though not true hibernation. They may wake every couple of weeks to eat.
#21. Brown Rat
- Rattus norvegicus
Look for Brown Rats anywhere people are living, particularly in urban environments. They’re best known for living in sewer tunnels and subway systems, scavenging food from the trash.
Believe it or not, this small mammal isn’t native to Pennsylvania. It’s thought to have originated in China and Mongolia.
Although many people find rats off-putting, others keep a sub-species of Brown Rats as pets. This subspecies, called the Fancy Rat, was bred specifically for the pet trade. Besides companion animals, rats can be trained for many jobs to assist humans, like detecting gunpowder for forensic teams and providing therapy support.
It’s a misconception that Brown Rats spread bubonic plague. In actuality, it’s more commonly spread through ground squirrels! Regardless, they can transmit infections of many kinds, as their blood can carry several diseases.
#22. Black Rat
- Rattus rattus
Interestingly, this small mammal is not native to Pennsylvania.
Instead, it’s thought that the Black Rat came from India and was transported to North America on cargo ships. It’s now so widespread that it’s no longer considered a foreign species.
It’s considered a pest in the agricultural market because it feeds on various crops. Like other rodents, Black Rats can carry pathogens in their bodies. While they may not appear sick, they can spread infections like toxoplasmosis, typhus, and bubonic plague.
In many areas where the Black Rat was once the dominant species, the Brown Rat has taken over. Black Rats are slightly smaller and reproduce less often, two of the reasons this species isn’t as widespread as Brown Rats.
#23. House Mouse
- Mus musculus
Few mammals in Pennsylvania thrive around people as well as the House Mouse!
House Mice have the characteristic large ears, thin tails, and tiny bodies of a typical “mouse.” They do incredibly well in highly populated areas, and there are now more semi-tame populations than wild.
House Mice are the most common species to find inside your home because they’re adaptable to human presence. They readily eat food scraps, build their nests in walls or dark attics and basements, and spend most of their time hidden from view. You’ve likely shared your home with a House Mouse at least once over the years. Although most people would prefer not to have them, they aren’t the worst roommates!
Like their eating habits, they are adaptable in their social behavior. House Mice with an excess of food, like those living in buildings, form a hierarchy with leaders and followers. However, in the wild, where food is less plentiful, females aggressively protect their territory from one another.
#24. White-footed Deer Mouse
- Peromyscus leucopus
Like most other mice, this species is a vector, which means it carries and spreads disease.
Many rodents can carry disease-causing pathogens without getting sick, making them ideal carriers for these germs. For example, White-footed Mice transmit hantavirus and the bacteria that cause Lyme disease.
White-footed Deer Mice are one of the most likely species you will find in your attic, garage, or basement. Even though they can spread disease, contamination isn’t very common in homes.
This is the species I’ve found in my house, and I use a live trap and release them in a field a few miles away. Here’s the trap that I use!
#25. American Beaver
- Castor canadensis
- Adults are 29 to 35 inches long, with a tail length between 7.9 and 13.8 inches, and weigh between 24 and 71 pounds.
- They have a dark brown coat of waterproof fur, webbed feet, and a large, flat, black tail.
- Their large, continuously growing incisors (teeth) are orange due to thick layers of enamel.
The American Beaver is North America’s largest rodent!
These incredible mammals are known as ecosystem engineers, meaning they’re one of just a few species that actively work to alter their habitat. They do so by building dams with trees, branches, and mud. Beavers use the dams for shelter, food storage areas, and dens for raising young.
Ponds created by beaver dams serve as important habitats for many types of wildlife. They also help reduce erosion and slow water movement, promoting moisture in drought-prone areas. Especially in northern climates, the water in the pond needs to be deep enough that it doesn’t freeze solid, allowing the beavers to swim under the ice all winter.
Beavers are excellent swimmers and can stay submerged for up to 15 minutes. They spend as much time as possible in the water, where they are less vulnerable to predators. This species uses its large tail to slap the water to signal danger to other beavers, as well as fat storage.
#26. Virginia Opossum
- Didelphis virginiana
- Adults measure 13 to 37 inches in length.
- Their fur is whitish underneath and dull grayish-brown on top though it varies throughout their range.
- They have white faces, long, hairless tails, and feet with opposable thumbs.
The Virginia Opossum is the only marsupial mammal in Pennsylvania!
They occupy various habitats but generally prefer forests and thickets near a source of water. This species adapts well to human presence, so you’re likely to find them in rural, suburban, and urban environments, including your yard.
Although many people consider the Virginia Opossum a pest, they provide an important service to humans! Insects, including ticks, are a staple food for opossums. They’re incredibly good at grooming and eat 95% of ticks that try to feed on them, up to 5,000 ticks in a single season. So, the next time you’re worried that an opossum is roaming your yard, remember they reduce your chances of tickborne illness.
This species is known to play dead or “play possum,” a unique tactic they’ve become known for. They go into a catatonic state, drool, and exude a noxious substance from their anal glands, feigning death.
As marsupials, Opossums give birth to relatively undeveloped young, which they carry in a pouch on their belly until they’re more developed. The young opossums are only about the size of a kidney bean, but they crawl into the pouch without assistance. Even though litters can be made up of 25 babies, only a small percentage survive.
#27. North American Porcupine
- Erethizon dorsatum
- Adults range from 2 to 3 feet in length and weigh about 20 pounds.
- Their fur ranges in color from brownish-yellow to black, with white highlights on their quills.
- Porcupines are covered in approximately 30,000 hollow quills.
While North American Porcupines generally spend much of their time on the ground, they can also climb trees, using their tail for support. But they aren’t the best climbers; one study found that 30% of the porcupines had healed fractures from falling from trees.
They’re well known for their sharp quills used for defense. When threatened, porcupines draw up the skin of their back, bristling so that the quills face all directions. The porcupine keeps its back to the predator and moves its tail back and forth. But, despite their effective defense, porcupines are still preyed on by fisher cats, coyotes, wolverines, and other predators that have adapted to hunting them.
Contrary to popular belief, porcupines can’t throw quills at their attacker! 🙂
#28. American Mink
- Neogale vison
- Adults measure between 12 and 18 inches long, have 6 to 10-inch tails, and weigh between 1 to 3 pounds.
- They have a long sleek body, short stubby legs, long neck, small ears and eyes, slightly webbed feet, and a long thick tail.
- Their fur is brown to black, soft, thick, and covered with oily guard hairs that make it waterproof.
The small mammals can be found in Pennsylvania in forested areas near large water sources. Their dens are located on river banks, under logs and tree stumps, or at the base of trees. Their dens are always close to water.
Minks are voracious predators and feed on surprisingly large prey. Believe it or not, they can eat fish up to 12 inches long and kill coastal birds like seagulls and cormorants by drowning them. Their slightly webbed feet and streamlined bodies are powerful in the water, and they can swim for up to three hours without stopping! While they’re rarely far from water, they hunt on land and can climb trees.
Despite this species being regularly hunted for its fur, its population is stable. However, scientists have expressed concern about the effect of escaped domesticated Minks on wild populations. Released Minks can cause territorial issues with wild populations and may introduce weaker genetics by breeding with wild individuals.
Check out the video of a mink above!
#29. American Ermine
- Mustela richardsonii
- Adults typically range from 6.7 to 13 inches in length. Males are twice as big as females.
- In the summer, their coat is brown on the upper parts and white underneath but turns brilliant white in winter.
- They have slender bodies, small faces, short legs, and oval ears.
American Ermines were originally believed to be a subspecies of the Beringian Ermine or Stoat (Mustela erminea). However, in 2021, a study determined that it was a unique species with distinct genetic features.
These mammals occupy various habitats in Pennsylvania, including forested, herbaceous wetlands, grasslands, and mixed woodlands. Though they prefer to prey on small mammals, they’re quite opportunistic and will also feed on worms, insects, and berries.
Male American Ermines maintain large territories that typically overlap with multiple females. Once fully grown, males disperse to find their own territories, while females remain in their birthplace throughout their lives.
- Martes pennanti
- Adults range from 29.5 to 47.2 inches in length. Males are often twice as large as females.
- Their coloration ranges from medium to dark brown with black legs and tail, gold or silver on their head and shoulders, and sometimes a cream patch on their chest.
- They have a long, slender body, stout legs, and a long tapering tail which accounts for 1/3 of their total length.
Although you might know it as the Fisher Cat, these animals are not felines, nor do they fish. 🙂 They are one of the larger members of the weasel family. Fishers thrive in forests with plenty of hollow trees for denning and high canopy closure to protect them from the elements.
Incredibly, Fishers are one of the few mammals in Pennsylvania that prey on porcupines.
Fishers attack porcupines on the ground, clawing the exposed flesh on their face and underbelly. Once the Fisher has weakened the porcupine, it goes in for the kill. Even though they’re difficult to kill, a single porcupine provides a Fisher with several days of food, making them worth the effort.
Between 1900 and 1940, Fisher populations fell dramatically, to the point of extinction in some parts of Pennsylvania. Unregulated fur trapping and intensive logging caused the depletion. However, in many areas, Fisher populations have since rebounded.
#31. Least Weasel
- Mustela nivalis
- Adults range from 6 to 9.8 inches in length.
- Their soft, dense fur is brown above and white below; in northern populations, they may molt to all white in the winter.
- They have a long slender body with short legs, prominent whiskers, and black eyes.
While Least Weasels don’t dig their own dens, they occupy abandoned dens from other species. They prefer those at the base of trees or near brush piles, tall grass, or other cover sources.
These mammals are highly specialized predators of small rodents. Species like voles, mice, and lemmings make up their entire diet when they’re abundant. However, Least Weasels are opportunistic and consume carrion, bird eggs, lizards, small fish, and invertebrates. They will forage at all hours of the day and night.
Least Weasels have a very large total population and are common in Eurasia. However, they are a much less common mammal in Pennsylvania and are now thought to require population management in the Southeast. In addition, least Weasels face threats from trapping as well as habitat and prey loss.
#32. Long-Tailed Weasel
- Neogale frenata
- Adults range from 8 to 10.5 inches long.
- They have brown upper parts and white to yellow fur on their undersides with a black tail tip, and in the northern parts of their range may become fully white in winter except for the tail tip.
- They have long bodies, small heads, short legs, and long whiskers.
Long-tailed Weasels have an extensive range across temperate and tropical habitats. They live in woodlands, open fields, farmland, and suburban areas. Usually, this species burrows in the ground, hollow logs, rock piles, or under barns, but they may also take over abandoned burrows created by other animals. Look for them near a source of water like a river or pond.
These weasels have a high metabolism and need to eat up to 40% of their body weight daily. They mainly feed on small rodents like voles, mice, chipmunks, and gophers, tracking their scent and crushing their skulls with their canines.
Long-tailed weasels are normally solitary, and they aggressively defend their territories. Unfortunately, due to interspecies aggression and predation, many Long-tailed Weasels die before they reach one year old. If they reach adulthood, they may live for several years, but their lifespan in the wild is not well studied.
#33. Big Brown Bat
- Eptesicus fuscus
- Larger-sized bat with around a 12-inch wingspan.
- Brown fur with black ears, wings, and feet. Wings are hairless.
These flying mammals are widespread in Pennsylvania.
If you know where to look, you’ll find Big Brown Bats inside caves, tunnels, or other human structures.
Big Brown Bat Range Map
This nocturnal bat primarily eats insects, especially ones that fly at night. However, their preference is to eat beetles. The Cucumber Beetle is their favorite, which benefits farmers because these insects are terrible pests for agriculture. Many farmers in Pennsylvania even use bat boxes to attract Big Brown Bats to their property!
Though rabies is common in all bats, research has shown the disease is rarer in this species. The reason for this fact is that many Big Brown Bats have immunity to rabies. Interestingly, researchers discovered that these rabies antibodies get passed down from generation to generation!
If you want even more information about mammals, or need help with additional identification, check out this field guide!
Which types of mammals have YOU seen in Pennsylvania?
Let us know in the comments!