Northern Leopard Frog

Lithobates pipiens
Northern Leopard Frog

The Northern Leopard Frog is the only known amphibian at Ruby Lake National Wildlife Refuge.  This quiet, camouflaged frog is not easily noticed, but as both predator and prey it makes up an important part of the food chain on the Refuge.  Northern Leopard Frogs have become increasingly important in medical and scientific fields, and their susceptibility to pollution and climate change makes them invaluable as an indicator species for monitoring environmental effects.

Leopard frogs forage in grassy or wet meadows, often near the edge of water.  They use both ambush and active foraging strategies to take a wide variety of prey.  Adult frogs eat insect larvae, bugs, beetles, flies, moths, worms, leeches, snails, and slugs.  Tadpoles are herbivores that use their scraping mouthparts to feed on algae, rotting vegetation, and detritus. 

After emerging from hibernation in spring, male leopard frogs begin calling when water temperature reaches about 55°F, from shallow, open areas, where courtship and mating take place.  Females will deposit 600-6000 eggs, typically attached to aquatic vegetation near the water surface.  Egg hatching time is inversely correlated with water temperature, that is, the warmer the water, the quicker the eggs hatch.  Tadpoles may emerge within 3-10 days, depending on water temperature.  Tadpoles remain in these waters until they complete metamorphosis during midsummer at approximately 1 inch in length.  In the remaining months between metamorphosis and hibernation, first-year frogs may reach lengths of nearly 2 inches.  Northern Leopard Frogs typically reach sexual maturity by age two, and individuals older than 4-5 years represent a small percentage of the population.  These frogs overwinter by hibernating in small pits they dig in the bottom of streams, ponds, marshes and lakes. 

The Northern Leopard Frog is a species indigenous to the wetlands of Ruby Lake National Wildlife Refuge and specimens were collected from the marsh as early as 1927.   Early reports indicated populations in 114 locations in Nevada, but a more recent study show they now exist in only 15 sites across the state.  Though widely distributed across North America, the declining western population is genetically distinct from the eastern population and was petitioned for listing under the Endangered Species Act in 2006. 

Turn to the next page for information on threats to Northern Leopard Frog populations and how Ruby Lake National Wildlife Refuge can help. 

Threats  

 

One of the biggest threats to Northern Leopard Frogs at Ruby Lake National Wildlife Refuge is likely the widespread occurrence of non-native predatory fish, specifically bass and trout.  Mating adults, tadpoles and hibernating adults are susceptible to predation in waters inhabited by these fish.  It is also a possibility that hatchery reared trout can infect native amphibian populations with fungal pathogens. 

Water management practices also have the potential to affect Northern Leopard Frogs.  Periodic drying and reflooding of marshes helps stimulate abundant submerged aquatic vegetation the frogs and tadpoles can use to avoid fish predation.

Habitat management practices such as prescribed burning and controlled grazing are required periodically in wet meadows and bulrush marsh.  These practices remove the build-up of dead vegetation and recycle nutrients, allowing frog better access to increased insect populations attracted to lush, new plant growth.  Another threat to leopard frogs is the misuse of pesticides and herbicides.  Many pesticides are known to have adverse effects on frog populations, particularly when used near the water.

Studies are needed to determine the distribution and density of Northern Leopard Frogs on the Refuge.  Overwintering, breeding, and summer foraging sites must be identified, as well as movement corridors linking these habitats, in order to effectively manage this species.  Given the current trend of declining Northern Leopard Frog populations in Nevada and throughout the western United States, and the rapidity at which local populations have gone extinct, known threats should be eliminated in areas of the refuge where populations have been identified.  Specifically, this includes:

  1. Careful and limited use of herbicides, particularly near wet meadows and marsh edges
  2. using prescribed fire or other vegetation management methods (i.e. grazing or mowing) when necessary to prevent excess build-up of dead vegetation
  3. establishing bodies of water free of non-native predatory fish where frogs can safely reproduce, forage, and overwinter
  4. allow the periodic drawdown of marsh units to stimulate growth of dense aquatic vegetation

Facts About Northern Leopard Frog

Size: 2–5“

Lifespan: 2-4 years

Diet: larvae, vegetable matter and invertebrates / algae and rotting matter for tadpoles

Habitat: aquatic

Range size: 15 to 615 sq. meters

Distribution: across North America with distinctions between populations east and west of the Mississippi

Northern Leopard Frog