In such a small and densely populated state, it may come as a surprise to some that New Jersey is home to thousands of species of diverse wildlife.

New Jersey houses over 400 species of land-dwelling vertebrates, 336 marine fish species, 134 freshwater fish species, and thousands of terrestrial and aquatic invertebrate species, according to the state Department of Environmental Protection.

Some commonly spotted animals include white-tailed deer, raccoons, black bears, mallard ducks and hawks.

But what do some of these commonly spotted animals do when the temperature starts drop and snow begins to fall?

Some hibernate, some migrate and some have adapted to endure the state’s cold winters.

New Jersey’s hibernators

As described by the National Park Service, hibernation typically refers to going dormant during the winter. Although many go dormant in one way or another, in order to be a true hibernator, an animal must have a reduced metabolism, slower heart rate and lowered body temperature during the winter.

There are many species in New Jersey that go dormant or into hibernation during the winter months.

The first animal that probably comes to mind is black bears, but they are not true hibernators, since their body temperature does not drop, the park service says.

However, they do fall into a light sleep in their dens, dozing in and out for most of the winter. Bears do not eat, drink or pass waste during this time, causing them to lose 15% to 30% of their body weight. Female bears give birth during the winter. They then continue sleeping on and off while their cubs feed and they wait out the spring.

New Jersey has multiple species of amphibians that hibernate, including frogs, salamanders and toads. Most amphibians seek out spaces for hibernation. These spaces can include mud at the bottom of water, a burrow that they dig themselves into, between rocks, or in cracks in a log.

Another animal that goes mostly dormant during the winter and that we often see in New Jersey is raccoons, which enter a prolonged state of inactivity known as torpor. They will sleep for weeks at a time but cannot sustain themselves for the entire winter, so they come out every few weeks to eat and drink.

Additionally, some species of bat hibernate. During the winter you could find the majority of hibernating bats in caves or old mines.

New Jersey’s migrators

When you think of migration, the first animal that probably comes to mind is birds. The DEP says New Jersey is home to over 130 species of neotropical migrant birds, 80 of them being songbirds that you have likely seen or heard in your backyard. These birds migrate long distances each year between the tropics and their breeding grounds in North America.

Another example of a migrator in New Jersey is the monarch butterfly. Monarchs follow distinct migration patterns, traveling south toward Mexico each year during the cold months.

They can be spotted throughout New Jersey during the summer. At the beginning of the fall, massive numbers of monarch butterflies gather in Cape May before they begin their fall migration south.

Finally, there are plenty of sea creatures that pass right by the Jersey Shore on their way down south. Some species include the North Atlantic right whale, bottlenose dolphin and cownose ray.

New Jersey’s year-round species

Though many species go dormant or leave New Jersey, there are a number of species that have adapted to survive the cold weather and food scarcity.

One of the most common examples is the white-tailed deer, which can be found all over New Jersey year-round.

During the winter, white-tailed deer do not hibernate or migrate, but they do have a variety of adaptations that allow them to survive even the harshest of winters:

• Their winter fur coat is made of a wooly layer with dark hair on top. It is thicker, longer and darker than their summer fur, allowing them to retain heat and insulate themselves to keep warm during the winter.
• They build up fat reserves during the fall to combat food scarcity during the winter.
• Their metabolism drops to reserve energy and they decrease their movement, drawing from their fat reserves to avoid using excess energy to find food.
• They seek out shelter areas that are denser and more covered from the elements.

Bobcats, while rarely seen, do live in New Jersey and do not hibernate or migrate during the winter. They have a thick winter coat, and they slightly reduce their activity levels, focusing on their small size, balance and sharp claws to hunt rather than their speed. Bobcats are primarily nocturnal hunters, so they cozy up during the day in their dens and hunt from dusk to dawn.

Finally, while many birds are migratory, many are not. Bald eagles, which have made an amazing comeback in New Jersey over the last couple of decades, are extremely active during the winter, building or repairing their nests, as they lay eggs about two weeks into the new year.

More:These are the 10 most-common birds seen in NJ backyards. How many have you spotted?

Other bird species that typically do not migrate include mallard ducks, Cooper’s hawks, northern harriers, red-tailed hawks, cardinals and pileated woodpeckers.

So, if you are wondering where the birds went, if the bears are still around, and how the deer in your yard are surviving the harsh winter, don’t worry. They know what they are doing, and they will all be back to normal when spring arrives.