Throughout the Great Lakes Region, amphibians are vital to healthy ecosystems. Sensitive to environmental change, amphibians serve as bioindicators, utilized by ecologists to measure the level of pollution within an ecosystem. In total, 6 species of typical frogs (genus Lithobates) are found in Ontario, including the Northern Leopard Frog (Lithobates pipiens), the Green Frog (Lithobates clamitans), the American Bullfrog (Lithobates septentrionalis), Mink Frog (Lithobates palustris), and Pickerel Frog (Lithobates septentrionalis). All of these except for the Pickerel Frog are found within the Long Point Basin. Most of these frogs prefer ponds and herbaceous marshes, but the Wood Frogs are usually observed around forested swamps.

Description 

Northern Leopard Frogs are large frogs, growing up to 11 cm in length. They are characterized by their smooth skin, which is usually green or brown, adorned with distinctive dark, irregular spots that are often surrounded by a lighter halo. A prominent light-colored dorsolateral fold (a raised ridge of skin) runs along each side of their back, extending from behind the eye to the groin. Their belly is typically white or pale green. Males are generally smaller than females and possess vocal sacs that inflate during their breeding calls. The tadpoles of Northern Leopard Frogs are greenish-brown and can grow relatively large before metamorphosis. Leopard Frogs widely vary in visual appearance, with a green morph, a brown morph, and a burnsi morph. Frogs of both the green and brown morphs possess black spots on their back reminiscent of a leopard, whereas the burnsi morph lacks dorsal spots, and may possess spots on their legs.

Ecology

In the Long Point Basin, Northern Leopard Frogs are most often found within their primary breeding habitat – herbaceous marshes, between April and October. They can also be found in swamps, creeks, and ponds, sometimes at a distance from visible water. Peak observation time is late summer. A walk in the marshes of Big Creek, Turkey Point, or Long Point between July and September can reveal hundreds of Leopard Frogs. They are known for their agility and characteristic “leaping” escape behavior. Leopard frogs will feed on a wide variety of organisms – especially insects and other arthropods. These include flies, beetles, grasshoppers, spiders, crickets and worms. Common predators of Leopard Frogs include racoons (Procyon lotur), snakes (Serpentes), and wading birds, especially, the Great Egret (Ardea alba) and Great Blue Heron (Ardea herodias) – of which, there is no shortage in the Long Point marshes, providing an abundance of great wildlife photo opportunities!

In November, Leopard Frogs begin overwintering. They prefer spending the winter months at the bottom of streams that are well-oxygenated. During hibernation, metabolism and other physiological functions slow down significantly. In April, Leopard frogs re-emerge in the spring. From their wintering sites, Leopard Frogs immediately begin moving to their breeding habitat. In April, male Leopard Frogs are busy pursuing the females by making a rattling snore-like, drawn out mating call. Vocal activity peaks in early May. During amplexus (copulation), females lay thousands of eggs in a combined mass measuring 6-9 cm in diameter, on aquatic vegetation close to water. Eggs hatch into tadpoles within 1-3 weeks. Tadpoles complete their transformation into small frogs by September, but do not reach sexual maturity until the end of the second summer. Northern Leopard Frogs live between 5-9 years in the wild, though many individuals succumb to predation earlier in life.

Conservation 

In some areas of southwestern Ontario, Leopard Frogs have experienced population declines. These declines are associated with wetland habitat loss and agricultural intensification (through clearing, drainage, etc). However, the opposite trend has been observed in much of the Long Point Region, where wetlands have been restored on marginal farmland through a collaborative effort encompassing conservation-minded landowners and organizations, including Long Point Basin Land Trust and Nature Conservancy of Canada. These ecological restoration projects have increased habitat for many species of wildlife, and their continuation highlights a regional commitment to nature conservation and healthy ecosystems in the Long Point Region!

Fun facts 

• Breeding calls of male Leopard Frogs change with temperature. While their main call is a snore-like sound, on cooler nights, the call may be shorter and less frequent. As the temperature warms, the calls become longer and more numerous, creating the characteristic spring chorus.
• The bulging eyes of Leopard Frogs are positioned on the sides of their head, giving them nearly 360-degree vision to help detect both predators and prey. They rely heavily on sight for hunting.
• Leopard Frogs will often remain completely still when they are threatened, attempting to blend into their surroundings. This camouflage and stillness can be effective against predators that rely on movement to spot prey.
• Leopard Frogs can respire through their skin, especially when submerged in water or in moist environments. This cutaneous respiration is essential for overwintering when their metabolic rate slows down and oxygen levels in their hibernation sites might be low.

 

Written by Matthew Palarchio, HBSc in Environmental Sciences, Western University

Photos (L-R): Canva stock photo, © David Bird, retrieved from iNaturalist, © T. Middleton, retrieved from iNaturalist

 

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