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This or That? – Furry Brown Mammal Edition

Written on: December 22nd, 2025 in Wetland Animals

By Alison Stouffer, DNREC’s Wetland Monitoring and Assessment Program

If you are like me, you have likely been driving down a rural road, paddling through a tidal wetland, or going for a stroll through a state park and seen a furry, brown animal that had you doing a double take. That wasn’t a weird looking dog all by its lonesome, was it? There are a handful of mammalian species that this animal could be, but they often look similar, if not identical. Read on to see if you can correctly identify these fury, brown mammals in a fun game of This or That? Answers can be found at the end of this blog post.

Round 1: Beaver or Groundhog?

For Round 1, you must decide which image belongs to the North American Beaver (Castor canadensis) and which belongs to the Groundhog (Marmota monax).

The North American beaver is the largest rodent in the United States and is considered a keystone species and ecosystem engineer due to its dam-building pastime, which significantly impacts the structure and function of the surrounding environment. For example, beaver dams – created from trees, sticks, and mud – create important wetland and floodplain habitats adjacent to open water, filtering out sediment and pollutants from the water column. These animals also rely on these wetland habitats as a source of plant-based nutrition for their herbivore diet. The North American beaver is easily identifiable by its long, flat, black tail and large front teeth. In addition to its tail, the beaver’s webbed feet, waterproof fur, and ability to hold its breathe for long periods of time make this animal suited to life in and around water.

The groundhog – also known as a whistle pig or woodchuck – is the most geographically spread marmot species in North America. Unlike the beaver, groundhogs are not typically found in wetland habitats. Instead, they prefer well-draining soil within forests and fields where they can build their dens and stay dry. Dens consist of a network of underground tunnels, which can provide habitat for other animals when abandoned. The groundhog is easily identifiable by its favorite posture – standing on its hind legs – and its short, bushy tail. These animals are also adapted to life underground, having strong claws for digging and short ears that flatten over the ear canal to prevent dirt from entering it while burrowing.

Round 2: Mink or Otter?

For Round 2, you must decide which image belongs to the American Mink (Neovison vison) and which belongs to the North American River Otter (Lontra canadensis).

The American mink has a geographic range that spans the entire continental United States, except for Arizona (I wonder what AZ did to deserve a mink exodus…) and are typically found in forested wetlands near streams, rivers, ponds, and lakes. These animals are well-adapted to their semi-aquatic habitats, using their waterproof fur and partially webbed paws to propel them through and under water to hunt for prey. The American mink – a carnivore – will eat small land mammals like mice and shrews, as well as fish, ducks, and frogs. When not in the water, they can be found hunkered down in their bankside burrows. As a wetland-reliant species, these animals are threatened by habitat loss and can be used as an indicator of wetland health.

The North American river otter inhabits most of the continental United States, except for more arid, desert states such as New Mexico, parts of southern California, and Texas. Like the American mink, North American river otters are found near aquatic habitats such as rivers and lakes; however, can tolerate both freshwater and saltwater and thus can be seen floating along the coastline or within saltmarshes . These animals are equipped to llive in the water, having nostrils that close and allow them to hold their breath for up to 8 minutes, webbed paws for swimming, dense fur for insulation, and whiskers that help them hunt in the water when other senses are reduced. The river otter is dependent on the waters adjacent to wetland habitats, relying on them for much of their diet (i.e., fish, amphibians, turtles, aquatic invertebrates, etc.).

Round 3: Muskrat or Nutria?

The common muskrat is native to North America and found throughout most of the continental United States but has been introduced – and become invasive – throughout parts of Eurasia. These large rodents are highly dependent on wetlands for survival; however, they can tolerate both fresh and salt water. Wetland habitats, such as ponds, lakes, marshes, and swamps, provide protection from the elements and food resources. Muskrats burrow underground within the banks of wetlands to create their homes, coming and going through underwater entrances. They also rely on their habitat for food, primarily consuming aquatic vegetation such as cattails. As a semi-aquatic animal, the muskrat is suited to the water as they have vertically flattened, scaled tails to help propel and steer them through the water, dense fur for insulation and buoyancy, slightly webbed back paws, and an ability to stay underwater for 12-17 minutes at a time.

Nutria are a rodent native to South America that were introduced to Eurasia and North America through the fur trade. In some part of the United States, nutria are considered an invasive species due to the damage that can be caused to irrigation infrastructure (i.e., dikes) from burrowing and competition for resources with native species, such as muskrat. Like muskrat, nutria are a wetland-dependent species that live primarily in freshwater marshes, lakes, and streams. They rely on wetland habitat for food, eating the roots, stems, and leaves of aquatic vegetation. These animals will also groom and feed off of DIY vegetation platforms and floating logs. Nutria, like muskrat, have dense fur for insulation, webbed back paws, and an ability to stay underwater for more than 10 minutes. However, their long tails are lightly covered in hair, rather than scales.

Hope you enjoyed the guessing game! The answers are below.

Round 1 – A) beaver, B) groundhog

Round 2 – A) otter, B) mink

Round 3 – A) nutria, B) muskrat

Tags: Animals, Education