Northern Leopard Frog
Northern Leopard Frog
Other names: Rana pipiens
The Northern Leopard Frog is a medium-large frog that can reach 13-15 cm in body length, although adults are more commonly 5-8 cm. They are typically green or brown with dark oval spots with light edges or “halos” over their back and the tops of their legs. It has light-coloured extending from the head to the groin. The upper lip has a white stripe that extends to the shoulder. The belly is white and may have a creamy-yellow tinge. Northern Leopard Frog tadpoles have long tails and a large tail fin. Tadpoles range from light brown to green with small gold spots and bronze bellies. Tadpoles typically metamorphose around 9 cm in length but may reach up to 12 cm.
Northern Leopard Frog Call
The call of the Northern Leopard Frog is a low snore followed by several low grunts that does not travel very far. It has been described as a “chuckling” or “gabbling” sound, or like a finger rubbed on a wet balloon.
In British Columbia, there are no other large frogs with large spots. In eastern Canada, Northern Leopard Frogs resemble the Pickerel Frog. The Pickerel Frog has more squared spots, a yellow belly, and is always brown.
The Northern Leopard Frog is part of a larger complex of very closely related species that are distributed across all of North America, however, only the Northern Leopard Frog is found in Canada. They are found throughout southern Canada and the north-central United States. In British Columbia, their distribution is very limited. At one time, Northern Leopard Frogs ranged widely in the East Kootenays, the Creston Valley, and the South Okanagan. Now, Leopard Frogs are only found in one location in the Creston Valley.
Northern Leopard Frogs hibernate over the winter and are active from April to October in southern Canada, with shorter active seasons at higher latitudes. They overwinter at the bottom of deeper water bodies that do not freeze solid. In many areas, Northern Leopard Frogs hibernate in different ponds from where they breed and may make migrations of up to 2 kilometers between these sites. Leopard Frogs are semi-terrestrial and have home ranges up to 600 m2, occupying a wide range of habitats including prairies, woodlands, and in some cases, tundra. Non-breeding adults are often encountered on land among low, dense vegetation that affords cover for resting during daylight hours. They tend to favour open, grassy areas which has led to them being sometimes known as the ‘Meadow Frog’. Breeding areas are typically permanent or semi-permanent wetlands, streams, or shallow sections of lakes and rivers. They prefer clear waters that are free of predatory fish.
Breeding occurs from mid-March to early June. Males will call to attract females. Fertilization occurs externally as the male grasps the female in. The female will lay globular egg masses 6-9 cm in diameter of up to 7,000 eggs. The egg masses are typically attached to aquatic vegetation near the surface and within a few meters of shore. Eggs are black on top and white underneath. Hatching time depends on water temperature, but occurs after 1-3 weeks. Tadpoles metamorphose 2-3 months later. Leopard Frogs do not reach sexual maturity until 2-3 years old, and likely do not live past the age of 5.
Northern Leopard Frogs typically forage at night on land and are indiscriminate predators, eating nearly anything that moves that will fit in their mouth. They are a sit-and-wait predator, waiting for a potential food item to come close before leaping 15-40 cm to seize the unsuspecting prey. Their diet is primarily composed of insects and spiders, though they may also eat snails, slugs, or other juvenile frogs. They have even been observed eating vertebrates like voles, birds, and garter snakes. Tadpoles are largely herbivores, grazing on algae.
In western Canada, the Northern Leopard Frog has dramatically declined over the last several decades. They nearly disappeared from Manitoba in the 1970s, and large declines have been reported from Alberta. There is some evidence of declines in Northern Ontario. In some areas, populations appear to have stabilized and a few have even increased. There is no confirmed cause of decline, but long-term drought and habitat loss are the suspected culprits. In British Columbia, the Northern Leopard Frog was never widespread, with only about 12 historic locations known. However, numbers have declined substantially since the 1970s, and by the mid-1990s only one population in the Creston Valley remained. Northern Leopard Frog declines in B.C. are mostly due to the conversion of wetlands for agriculture and other uses. It is likely that invasive plant species and introductions of predatory fish species and American Bullfrogs have also contributed to declines. In the Creston Valley, breeding adults are declining at alarming rates largely from Chytrid fungus infections. Dead adults have been found with sloughing skin and bleeding extremities characteristic of Chytrid fungus infection. Captive breeding programs are attempting to ‘head-start’ developing frogs by raising them in captivity and releasing adults into historically known locations. Northern Leopard Frogs are very sensitive to chemical pollutants like herbicides and pesticides that cause high rates of deformities. Due to their migratory behaviour to and from hibernation sites, road mortality can lead to the long-term decline of populations where roadways bisect their habitat.
Did You Know?
The Latin name pipiens means “peeping”. When Northern Leopard Frogs were first studied and collected, the people studying them heard peeping cries and named the frogs accordingly. However, the sounds were likely not even from the Northern Leopard Frog, but the Spring Peeper.
The colour of Northern Leopard Frogs (brown or green) is determined by a single gene with two alleles, with Brown being dominant to Green.
However, green is the most common colour of Northern Leopard Frogs in Canada, and the only colour recently reported in British Columbia.