Western Chorus Frog

(Pseudacris triseriata)

Status: Threatened- Canadian Shield population (COSEWIC 2008, SARA 2002)

Table of Contents:

Species Identification
Diet
Habitat and Range
Biology and Behaviour
Similar Species
Threats/Reasons for Being Endangered
Conservation and Recovery Strategies
How You Can Help

Species Identification:

The Western Chorus Frog is a small tree frog of about 2.5 cm long and weighs about 1 gram. They are light brown in colour and have a dark line extending their entire length, three dark stripes on their back, and a white line that runs along the upper lip. This frog is generally hard to find by sight but they are easy to identify from their call, which is similar to the sound of running your finger across the teeth of a comb. However, it can be difficult to distinguish when calling amongst spring peepers as they can sound similar.

Diet:

Like most frogs, the Western Chorus Frog is insectivorous, and will eat small invertebrates like flies, mosquitoes, ants, beetles, moths, caterpillars, grasshoppers, snails, slugs, and spiders. Tadpoles will feed on different types of algae. Western Chorus Frogs will forage for their food by remaining still and hidden, snapping up any food that comes within range.

North American Range

Canadian Range- both maps taken from the Government of Canada: https://www.registrelep-sararegistry.gc.ca/virtual_sara/files/cosewic/sr_western_chorus_frog_0808_e.pdf

Habitat and Range:

Roughly 9% of the global population resides in Canada. In fact, it is thought that the current occupation of Chorus Frogs is only 10% of their historical range. The Western Chorus Frog is generally only found in the lowlands of Southern Ontario and Southern Quebec. In the United States, the Western Chorus Frog can be found in the central and northeastern states, from Kansas and Oklahoma to Michigan and New York. The Carolinian population, which occupies most of Southern Ontario up into Niagara and the south end of the Greater Toronto Area, is not listed as At Risk since populations seem stable. The Canadian Shield population extends up from the northern boundary of the Carolinian population, into Bruce and Grey Counties, and then east through Ontario into Southern Quebec, and north through The Land Between.

Western Chorus Frogs prefer a variety of lowland habitats with temporary water sources such as flooded fields or vernal pools. They don’t have a particularly large range, averaging at about 3.5 m of travel a day to a maximum recorded distance of 42 m per day. Since they prefer only temporary water sources, they run a high risk of dehydration. Thus, the type of habitat that lies between hibernation and breeding locations has a direct effect on the viability of the population. Western Chorus Frogs will hibernate in soft soils under rocks or fallen trees that lie in their home range. A 2004 study in Quebec found that Western Chorus Frogs will generally hibernate within 100 m of their breeding grounds.

Biology and Behaviour:

The Western Chorus Frog emerges from hibernation and heads to their breeding grounds in late March. They will inhabit temporary water sources until late August when they dry up. This is thought to help lessen the prevalence of predation that occurs in more permanent wetlands. Chorus frogs tend to forage in more terrestrial habitats, and they can also often occupy sites with significant agricultural cover or urban land use if the vegetation characteristics are suitable.

Western Chorus Frogs will breed in early spring and begin calling in mid-March. Most calling occurs throughout the month of April, and can happen day or night, often in tandem with Spring Peepers. The female will lay a bunch of small egg sacks that attach to vegetation near water. Eggs will hatch within a few weeks and tadpoles will transform into frogs by early or mid summer.

Adults tend to only breed once in their life and they will only survive for a year. Although some have been thought to live up to 3 years, it is a rare occurrence.

Western Chorus frogs are prey to a variety of predators, including birds such as raptors and herons, predatory fish, and predatory reptiles like snakes.

Similar Species:

The Spring Peeper looks very similar in size and overall appearance. A defining attribute of the Spring Peeper is a dark “X” located behind the head. Although this “X” is not always present, the Western Chorus Frog can be differentiated by the three lines running down their back
The Boreal Chorus Frog used to be considered the same species as the Western Chorus Frog until 1989. They can be distinguished by both call and location- they have a shorter pulse rate when they call and their habitats do not overlap in Ontario

Threats/ Reasons for being at Risk:

1. Agricultural intensification: Agriculture has both currently and historically impacted Western Chorus Frog habitat. The increasing need for food has resulted in the draining, filling, and clearing of their habitat, and many flooded fields and vernal pools have been drained to increase crop production. While Western Chorus Frogs have been known to inhabit agricultural lands, recent divergence into vast monocultures has limited this ability.

2. Urban development: Urban development is another threat to Western Chorus Frog habitat, as human populations expand and develop outside of large cities. Urban development is expanding northward into The Land Between, which is the northern extent of the Threatened Canadian Shield population. Development also leads to an increase in roads, which are a threat to the Western Chorus Frog when it leads to mortality from getting hit by cars while trying to cross into other parts of their territory.

3. Fertilizers and pesticides: Pollution is another huge issue, from both an agricultural perspective and an urban one. Increased use of fertilizers and pesticides in agricultural fields are causing direct harm to Western Chorus Frogs that live in or around these fields. They can also be impacted by urban pesticides as people spray their property to control weeds or insects. Pesticides have also been linked to the global decrease in insect populations, which are the Western Chorus Frogs only source of food.

4. Climate change: Climate change causes increased flooding and drought events, both of which can harm the Western Chorus Frog. Since they prefer only temporary water sources, an increase or lack of them would impact their breeding success. Climate change also leads to an increase in extreme weather events and sudden changes in temperatures, both of which can lead to mortality if it gets too cold or too hot.

Conservation and recovery strategies:

Since the Canadian Shield population is listed as Threatened, both the species and their habitat are protected. Next steps to increase populations are to protect their current known habitats and rehabilitate any areas that can support them. This is done through land acquisition and stewardship. The Federal Government is also working to try and reduce the use of harmful fertilizers and pesticides, especially in the agricultural sector. There are also a great deal of knowledge gaps with the Western Chorus Frog. More surveys and monitoring protocols have been put in place for Ontario and Quebec, and people are encouraged to report any sounds or sightings. Historical locations of the Western Chorus Frog are also being researched, and strategies are in place to limit urbanization in these areas.

How can you help?

Keep your property natural, avoid clearing any rocks or fallen trees, and encourage temporary flooding and vernal pools.
Keep an eye out for frogs on the road when driving at night during or after rainfall.
Report sightings to iNaturalist.
Avoid using harmful chemicals like fertilizers and pesticides on your property.
Educate others about reptile and amphibian stewardship!

Additional Resources:

Ontario Nature’s Western Chorus Frog page
Government of Canada’s population recovery strategy
The Western Chorus Frog page from the Canadian Herpetological Society
Information about Chorus Frogs from Hinterland Who’s Who

Sources:

COSEWIC. 2008. COSEWIC Assessment and Update Status Report on the Western Chorus Frog Pseudacris triseriata in Canada Carolinian population Great Lakes/St. Lawrence – Canadian Shield population. Ottawa. vii + 47 pp. (www.sararegistry.gc.ca/status/status_e.cfm).

Environment Canada. 2015. Recovery Strategy for the Western Chorus Frog (Pseudacris triseriata), Great Lakes / St. Lawrence – Canadian Shield population, in Canada, Species at Risk Act Recovery Strategy Series, Environment Canada, Ottawa, vi + 50 pp