Colorado is a landlocked state situated in the Mountain West subregion of the western United States. It is described as having a ‘cool, dry, and invigorating climate’, with abundant sunshine and low precipitation – winters are generally mild, while summers remain cool.
This state boasts an enormous variety of habitats, including grasslands, riparian areas, and forests, as well as extensive water systems. The Colorado River flows through the state, as well as the Green and Arkansas rivers. In addition, there are many lakes such as the Blue Mesa Reservoir and Grand Lake. These habitats provide suitable conditions for frogs to forage and reproduce, and around nine different species are found within the state.
Colorado Frogs
1) Northern leopard frog (Lithobates pipiens)
- Native to southern Canada and the northern US
- Family: Ranidae
- Order: Anura
- Conservation status: Least concern
The northern leopard frog grows to lengths of 6.4 – 7.6 cm (2.5 – 3 in) and has a slender build with a small head. The body of this frog is green or brown in color, with dark spots across the back, and a white or cream underside. There is a pale stripe on the upper lip, and another running from the eye, along the dorsolateral folds.
Lithobates pipiens is widespread in Colorado, with just a handful of counties where it hasn’t been recorded. Populations can be found at elevations of 3,000 – 12,000 ft, where they occupy wet meadows, marshes, ponds, and streams. Being opportunistic carnivores, individuals consume an enormous variety of prey, including grasshoppers, beetles, other frogs, lizards, snails, and spiders.
Despite being widespread, there is evidence to suggest that northern leopard frogs have declined in Colorado. Pathogens, development, and invasive species such as the bullfrog may have played a role in population losses.
2) American bullfrog (Lithobates catesbeianus)
- Native to eastern North America
- Family: Ranidae
- Order: Anura
- Conservation status: Least concern
The American bullfrog is very large, reaching 11.4 cm (4.5 in) in length. This frog has a heavy body and large tympana, which are even bigger in males. The skin is bright green, tan, or olive-brown in color, with darker mottling across the dorsum, while the underside is cream or white with some mottling.
Lithobates catesbeianus can be found in east and west Colorado – there are few records for populations in the center of the state. American bullfrogs are an invasive species in Colorado, causing extensive damage by outcompeting and even preying on native frog species. Some communities are working together in an attempt to reduce the number of these frogs and restore ecosystems to their natural state.
This species prefers areas with a permanent body of water, often residing amongst dense emergent vegetation. Bullfrogs are ambush predators that will tackle whatever is available, including crayfish, fishes, birds, small mammals, reptiles, and insects.
3) Canyon treefrog (Hyla arenicolor)
- Native to the southern US
- Family: Hylidae
- Order: Anura
- Conservation status: Least concern
The canyon treefrog is small, growing to lengths of just 2.5 – 5 cm (1 – 2 in). Individuals have quite rotund, broad bodies, with tan, gray, or olive-colored skin covered in dark blotches, and yellow on the insides of the hindlegs. In the sunlight, they are described as appearing golden-colored.
The range of this species in Colorado is limited to the far west, in the Colorado River and Dolores River drainages, and southeast, in Las Animas County. Its habitat preferences include riparian zones in rocky canyons, as well as along streams within grassland or oak-pine forest. The diet of this frog includes ants, spiders, beetles, and flies.
During the breeding season, males call to attract females. Research has found that the calls differ depending on the geographic location of that population, and females can distinguish between the different lineages. Females lay more than 100 eggs at one time, which hatch around two weeks later.
4) Wood frog (Lithobates sylvaticus)
- Native to northern North America
- Family: Ranidae
- Order: Anura
- Conservation status: Least concern
The wood frog ranges in length from 3.8 – 8.2 cm (1.5 – 3.2 in) and has a slender build with prominent dorsolateral folds and long hindlimbs. The coloration of the skin varies – it can be brown, red, green, or gray, and females are typically more vibrant than males.
Lithobates sylvaticus is classified as a species of special concern in Colorado, and populations within the state are small, rendering them susceptible to human activity and disease. This species resides in a variety of habitats, including coniferous forests, swamps, and oak-hickory or beech-maple forests. Individuals consume spiders, insects, worms, slugs, and snails.
The wood frog possesses the remarkable ability to withstand freezing. Although individuals seek shelter by burrowing under leaf litter, they may often be exposed to these extremes of temperature. This species has biochemical adaptations that enable it to use glucose as a cryoprotectant.
5) Boreal chorus frog (Pseudacris maculata)
- Native to North America
- Family: Hylidae
- Order: Anura
- Conservation status: Least concern
The boreal chorus frog is a small anuran with smooth skin. It typically grows to around 4 cm (1.6 in) in length, and its coloration varies from green-gray to brown, with a paler underside. Other distinctive features include a dark stripe traveling through the eye, and a white stripe on the upper lip.
Pseudacris maculata can be found throughout Colorado, although its distribution is reported to become more fragmented towards the southeast corner of the state. This species prefers grassland or forest, where it has been found to associate with areas with abundant cover and plenty of dissolved oxygen.
Boreal chorus frogs breed in shallow, fishless bodies of water, where the females deposit their eggs, adhering them to emergent vegetation. In areas where boreal chorus frogs overlap with wood frogs, wood frog tadpoles may limit the growth and productivity of Pseudacris maculata larvae.
6) Plains leopard frog (Lithobates blairi)
- Native to North America
- Family: Ranidae
- Order: Anura
- Conservation status: Least concern
The Plains leopard frog attains lengths of 5 – 9.5 cm (2 – 3.7 in), with females usually being significantly larger than males. This frog is brown or green in color with large brown spots across the back, a white stripe on the lip, and yellow dorsolateral folds. The underside is white, and there are dark bands along the hindlimbs.
Lithobates blairi occurs in the eastern half of Colorado, where it occupies uplands, wet meadows, and riparian areas. Individuals may be observing basking on vegetation mats at the edges of streams or ponds. The diet of this species includes insects, mollusks, crustaceans, and other amphibians and snakes.
Populations of the Plains leopard frog are declining, likely due to agriculture, invasive species, and pollution. Protection of breeding and overwintering sites, and maintenance of migratory pathways are two methods suggested for the conservation of this species.
7) Northern cricket frog (Acris crepitans)
- Native to the US and northeastern Mexico
- Family: Hylidae
- Order: Anura
- Conservation status: Least concern
The northern cricket frog reaches 1.6 – 3.5 cm (0.6 – 1.4 in) in length and has long hindlimbs. This frog’s skin is often covered in warts and ranges in color from green to gray to brown. There is a brown or orange stripe running down the back, and a triangular-shaped mark on the top of the head.
Acris crepitans is found in the easternmost part of Colorado, where it occupies moist habitats such as the edges of ponds or streams, in areas with plenty of vegetation. Although populations of this species are stable overall, within the state they may face challenges such as pollution from agriculture, predation by bullfrogs, and habitat degradation.
During the winter months, northern cricket frogs hibernate in terrestrial habitats that provide them with protection against freezing. They are not capable of withstanding extremes of temperature so rely on protection from their environment, utilizing spaces such as crayfish burrows or cracks in banks.
8) Western chorus frog (Pseudacris triseriata)
- Native to North America
- Family: Hylidae
- Order: Anura
- Conservation status: Least concern
The western chorus frog is small, growing to just 2.5 cm (1 in) in length. This frog has smooth skin which is green-gray or brown in color, and there is a dark stripe running through the eye, and a white stripe on the upper lip. Another distinctive feature is the three dark stripes running down the back, which may be broken into spots.
Pseudacris triseriata is widespread in Colorado in areas up to 12,000 ft in elevation. It occupies forest openings near ponds or streams – these are essential for the frog’s reproduction and provide habitat for the tadpoles as they mature. Interestingly, tadpoles from streams have been found to undergo metamorphosis sooner than those from other habitats.
Common food items for the western chorus frog include plant matter, spiders, snails, and shed skin. Individuals often forage by remaining very still, ready to ambush their prey when it gets close enough.
9) Blanchard’s cricket frog (Acris crepitans blanchardi)
- Native to the central and southeastern US
- Family: Hylidae
- Order: Anura
- Conservation status: Least concern
The Blanchard’s cricket frog is a small frog that reaches just 1.3 – 3.8 cm (0.5 – 1.5 in) in length. It has warty skin which may be gray, tan, green, or brown in color, with a red, yellow, or orange stripe down the back. Three distinctive features can be used to identify this species: light and dark bars on the upper jaw, a dark triangle between the eyes, and a black or brown stripe along the inside of each thigh. The underside is white.
There is just one population of Acris crepitans blanchardi in Colorado, which is confined to a small area in the northeast of the state. Its range in the state was once much wider, however it has declined and is now absent from many areas. Reasons for this decline may include development, agriculture, and construction of dams.
This frog prefers habitat around the margins of ponds, streams, or lakes, with an abundance of aquatic vegetation and muddy substrate. The diet of this species includes gastropod mollusks, insects, and isopod crustaceans.
