They’re small, and only five species are known to occur in the NWT, but amphibians play an essential role in ecosystems—and globally, they are declining at rates that are unmatched among other vertebrates (animals with backbones).
Two of the five species are listed as species at risk. The Northern Leopard frog and the Western toad are listed as Threatened in the NWT under the Species at Risk (NWT) Act. They are also listed as species of Special Concern under the federal Species at Risk Act. While the other species, including the two amphibians found in Wek’èezhìı –the Boreal Chorus Frog and the Wood frog-- and the Canadian toad, are not currently assessed as species at risk, they share several threats in common.
An NWT-wide management plan was developed to help conserve these species at risk and address the needs of all amphibians in the territory. The Board provided comments on the draft plan in August and at its November 2016 meeting, approved the NWT Amphibians Management Plan. The Management Plan is not publicly available until the Minister releases it in February 2017.
Frogs, toads and other amphibians are cold-blooded, taking on the temperature of their surroundings, and live part of their lives in water and part on land. Their name “amphibian” actually means “two lives”. They need aquatic habitat for breeding, egg laying and development of their young. They also need habitat on land for foraging and overwintering. Moreover, amphibians need to be able to move freely between these habitats as they often return to the same breeding or overwintering sites each year.
Elsewhere in Canada, the main threats to amphibians are habitat loss and pollution. Droughts, increased exposure to ultraviolet (UV-B) radiation due to ozone thinning in the atmosphere, and diseases could also be affecting amphibian populations. Many frog species depend on temporary water sources for breeding. Under drought conditions, these spring-time pools could dry up before their young develop, and a generation of frogs could be missed. Because amphibian eggs lack shells, and adults and young have thin, delicate skin, they are sensitive to increased levels of UV-B radiation. For many amphibian species, increased exposure to UV-B radiation can hamper the hatching success of eggs—particularly eggs that are laid in open shallow water and are directly exposed to sunlight. Additionally, diseases such as chytrid fungus and ranavirus have been known to cause amphibian declines.
Both these diseases have also been found in the territory and are a significant threat to NWT amphibians. Human activities that disturb habitat such as breeding ponds and overwintering habitat, or prevent amphibians’ movements can also have negative effects on their populations. Predation, especially in early life-history stages, and accidental deaths where vehicles or other human activities overlap with areas where amphibians are found together, such as breeding sites, also present threats.
Amphibians are essential members of the ecosystems in which they live. They consume a variety of insects and other invertebrates, and they act as prey for other species. A wide range of wild mammal and birds rely on frogs, for example, as part of their diet. Frog tadpoles feed on algae, small aquatic plants, preventing “blooms” (when algae grow out of control) that can reduce oxygen levels in ponds. And because they are sensitive to changes in their environment, amphibians can act as indicators of ecosystem health and habitat quality. Amphibians require suitable habitat in both their terrestrial (land) and aquatic (water) environments. They are connected to water at one or more stages in their life cycle, and, as adults, emerge from hibernation to breed in wetlands. Most amphibians change into terrestrial adults and breathe through lungs and the moist outer layer of their skin. Their lifestyle makes them especially vulnerable to changes in the air, water, or land –and they are one of the first living creatures to be affected by any changes in their environment.
The plan’s goal is to maintain a healthy and viable population for each amphibian species across its range in the NWT. One of its objectives is to identify and maintain key amphibian habitats. Monitoring and managing the effects of disease and other significant threats, and learning more about NWT amphibians from traditional, community and scientific knowledge are also important objectives. Here’s some information about the two amphibian species found in Wek’èezhìı, the Wood frog and the Boreal Chorus frog.
A small brown frog with a dark eye mask in the woods is likely to be a wood frog. Because of its distinctive mask, this frog has been called the "robber frog" and "bandit frog". (Photo: Ontley / Wikimedia Commons: CC BY 3.0)
Although amphibians are mostly found in the forested areas of the NWT, the hardy Wood frog can also be seen just north of the tree line (the farthest north trees can grow). In fact, Wood frogs occur further north than any other amphibian in North America, and are the only frog that lives north of the Arctic Circle. (See NWT distribution map here (Map: Environment and Natural Resources, GNWT). Adults usually live in woodlands and lay eggs in “vernal” (spring-time) pools. During winter, they hibernate and take shelter in leaf litter beneath snow cover.
Wood frogs can withstand the cold by freezing over the winter—and surviving! In winter hibernation, their physical processes slow down to a near stop, allowing them to conserve energy. These tiny amphibians can survive for weeks with an incredible two-thirds of their body water completely frozen during its winter hibernation. In a phenomenon that is not completely understood, the Wood frog is able to endure cold temperatures by producing a natural “antifreeze” that keeps the frog’s vital organs from becoming totally frozen. Increased blood sugar in the tissues appears to resist freezing, while water outside the cells turns to ice. When the weather warms back up in spring, the frogs thaw out and come back to life, feeding and mating again.
Adult Wood frogs eat a variety of small, forest-floor invertebrates, such as insects, spiders, worms and snails, and fall prey to coyotes, foxes, and birds. They spend summer months in moist woodlands and forested wetlands, and in fall, migrate to neighbouring uplands for the winter. In early spring, they emerge from hibernation and migrate to nearby thawed pools.
(Photo: Tnarg 12345 / Wikimedia Commons: CC BY SA-3.0)
The tiny Boreal Chorus frog lives in damp, grassy or woody areas near woodland ponds, but its habits are not well known. It belongs to the group of tree frogs, but in actual fact, it isn’t a strong climber, rarely climbing above the height of tall grasses or low shrubs, hunting for food – small invertebrates including ants and spiders--in low vegetation or on the ground. Adults grow to only 2-4 cm long—no more than the width of two dimes side by side. They may be almost any colour, including grey, tan, brown, red, olive, or green. Their tiny size and colour make these secretive frogs hard to spot in the woods. Nonetheless, they fall prey to birds, large insects and small mammals like mice.
In summer, these frogs hunt mainly at night, resting under leaves at the base of willows or brush in the day. They spend winter under the leaves or logs on the forest floor. Like the Wood frog, Boreal Chorus frogs can endure cold temperatures and emerge from hibernation in early spring, arriving at breeding ponds even before all the ice has melted. Males gather in large groups in spring to call for mates; at the height of breeding season, these choruses can heard day and night. More often heard than seen, their relatively loud calls are a sign that spring is here.
See map showing distribution of Boreal Chorus frogs in the NWT here (Map:Environment and Natural Resources, GNWT)