A true herald of spring, the wood frog is one of the first sounds commonly heard when the days start to warm. In the spring, it can be found in the marshy areas of Harbor Island. The males rattling, quick quacks signify its desire to mate. Once these little, black masked frogs have mated for the season they are off to the forest as their name suggests. Brown, like the color of fallen leaves, they will spend the summer, fall and winter in the woods. Much like a chameleon, these frogs can darken or lighten their skin to help them blend into the background to avoid the eyes of hungry predators and mask them from their prey. To survive the winter, these little frogs do something amazing; they freeze solid and are able to thaw out in the spring to resume their froggy ways.

An old favorite, the white-tailed deer, can be found on the island. Although not often seen, signs that deer are present can be readily observed. While hiking on the island watch for the telltale tracks and piles of scat that look much like a pile of chocolate covered raisins. Another sure sign of deer presence is to look at the cedar trees. When deer populations are high, a visible browse line is present. Deer are, if nothing else, consistent gardeners who under the right circumstances prune cedar trees to a uniform height. In general, this height is as high as a deer can reach in the winter with the assistance of the snowfall. On Harbor Island, this browse line is not as noticeable as it is in other parts of the state, but does occur in patches.

The beautiful patterns of contrasting black, dark brown or reddish saddles on lighter tan, brown or gray background help to distinguish young northern water snakes from other snake species in the Great Lakes Region. Aging northern water snakes tend to darken over time until they become a near uniform color making it difficult to see the pattern. Able to stay underwater for over an hour at a time, this snake hunts small fish, frogs and a variety of other prey. Often persecuted for eating sport fish, these snakes generally feed on smaller, slow moving or ill fish, and often eat dead fish that wash up on the beach. This snake has a reputation for being ill tempered when approached and, although it is not venomous, it can deliver a nasty bite. When observed from a distance these fascinating reptiles can be seen swimming, sunning themselves on rocks or branches, and even feeding.

The horseshoe shaped Harbor Island National Wildlife Refuge is dominated by northern white cedar and balsam fir forest. Cedars, and to a lesser extent, balsam fir are an important winter food source for animals such as the white-tailed deer. Red squirrels harvest cones from the trees and leave little piles of pine cone parts scattered under their perch as they eat the seeds. Woodpeckers and warblers are known to feast on the insects that feed on the trees. Balsam fir provide nesting habitat for birds such as the evening grosbeak and the yellow-rumped warbler. The cedar / balsam fir forest also provides habitat for several plant species including protected orchids.

The mixed hardwood forest at Harbor Island National Wildlife Refuge is comprised mainly of red oak, sugar maple, trembling aspen, ash and paper birch which are found in pockets scattered throughout the island. The largest tract is located on the south shore with the other areas adjacent to the interior harbor. At one time, there was at least one home located on the island that was removed when the island was purchased for conservation. Two open fields, relics from a time when people were there, will be allowed to naturally regenerate. Northern hardwood forests provide habitat for spring woodland wildflowers, such as twinflower and bunchberry. Common northern hardwood forest residents include black-throated blue warbler, black-capped chickadee, white-throated sparrow, cedar waxwing and snowshoe hare.

Much of the interior harbor and northeastern parts of the island are marshland comprised of sedges and rushes interspersed with wetland wildflowers such as great blue lobelia, swamp milkweed and boneset. This marshy habitat provides the perfect home for a number of wetland bird species such as the pied-billed grebe, mallard, wood duck, and other wetland birds. In the spring the marshes are full of frogs and toads that visit the water to mate and lay their eggs before returning to their woodland homes.