Description of Residence for the Western Chorus Frog – Great Lakes, St. Lawrence- Canadian Shield Population (Pseudacris triseriata) in Canada

The following is a description of residence for the Western Chorus Frog, Great Lakes, St. Lawrence – Canadian Shield population (Pseudacris triseriata, hereafter Western Chorus Frog), created for the purpose of implementing section 33 of the Species at Risk Act (SARA) which relates to the damage or destruction of residences.  Such damage or destruction can result from any alteration to the topography, geology, soil conditions, vegetation, chemical composition of air/water, surface or groundwater hydrology, micro-climate, or sound environment which either temporarily or permanently impairs the function(s) of the residence of one or more individuals.

Western Chorus Frogs have two types of residences – breeding site and hibernating site.

Figure 1. Global range of the Western Chorus Frog (adapted from COSEWIC 2008).
Map of Global range of the Western Chorus Frog
Long description for Figure 1

The range of the Western Chorus Frog extends from southwestern to northeastern North America. In the United States, the species occupies a vast area stretching from Kansas and Oklahoma to northern New York and Michigan. In Canada, the Western Chorus Frog is found in the lowlands of southern Ontario and southern Quebec.

1) Breeding site

Physical Appearance and Context

Western Chorus Frogs breed in temporary wetlands or shallow portions, which become dry in the summer, of permanent aquatic features (e.g., ponds, basins/potholes, marshes, swamps, drainage ditches; COSEWIC 2008).  Egg masses are attached to vegetation or twigs (although they may simply sink below the surface of the water) (Pack 1920; Whitaker 1971; Hecnar and Hecnar 1999; Desroches and Rodrigue 2004).  The submerged plant, dead grass stem or twig on which the eggs are deposited is considered a breeding site.

Period and Frequency of Occupancy

Depending on weather conditions, Western Chorus Frog will start breeding as soon as the end of March (Francis 1978; Bishop et al. 1997; Lepage et al. 1997; Desroches and Rodrigue 2004). Once the eggs are layed (end of March to mid-May), it takes 3 to 27 days for them to hatch into tadpoles depending on temperature (Whitaker 1971; Desroches and Rodrigue 2004).  Accordingly, a breeding site can be occupied (i.e. eggs are present) starting March 20th until June 11th.

Although breeding sites occupy very limited areas, they can be distributed throughout the wetlands within which they occur. These wetlands have been shown to range from 0.001 to 6 ha in Quebec (Picard and Desroches 2004; St-Hilaire 2005).  The same wetlands or aquatic features are generally used from year to year to house Western Chorus Frog breeding sites.  Accordingly, any wetland or aquatic feature occupied or known to have been occupied by Western Chorus Frog during any life stages is considered as containing at least one occupied residence.  Thus, it is not necessary to confirm the presence or exact location of a breeding site; this is not advisable since confirming the presence of breeding sites is also very likely to damage or destroy them.  Only when the habitat no longer exists or the absence of Western Chorus Frog from a specific wetland or aquatic feature has been demonstrated is the area considered to no longer contain a Western Chorus Frog nest site.

Damage and Destruction of the Residence

Although the remainder of the wetland or aquatic feature within which the breeding site is found is not considered part of the residence, it is needed to maintain the essential characteristics and function of the breeding site. Temporary wetlands or shallow portions, which become dry in the summer, of permanent aquatic features (e.g., ponds, basins/potholes, marshes, swamps, drainage ditches) provide the conditions (e.g., range of temperatures, hydroperiod - presence of water in the habitat, residual vegetation) required for the eggs to develop into tadpoles.

To ensure that breeding sites are available from one year to the next and to maintain the functionality of the breeding site, the ecological integrity of wetlands and aquatic features containing breeding site must be maintained.  As such, activities which may damage or destroy the breeding site include those which directly affect the breeding site as well as those which affect the wetlands or aquatic features and therefore the functionality of the breeding site.  These latter activities can occur at any time during the year.

2) Hibernating site

Physical Appearance and Context

Western Chorus Frog hibernation takes place in terrestrial habitats (e.g., lowlands such as pastures, clearings, meadows, fallow lands, shrublands, wooded areas) in soft soil substrates, under rocks, dead trees/branches, leaves/litter or in existing burrows (Froom 1982). Accordingly, any one of these sites used by hibernating Western Chorus Frogs is considered a hibernating site.

Period and Frequency of Occupancy

In Canada, the Western Chorus Frog generally hibernates from October to March (COSEWIC 2008) depending on weather conditions. Accordingly, a hibernating site can be occupied October 1st to March 20th.  Most observations tend to confirm that hibernating sites are relatively close to the wetlands where Western Chorus Frogs breed. Cochran (1989) observed individuals at the edge of a dried temporary pond and others as far as 75-100 m from the nearest wetland. In a study of individuals tagged with Co60, a radioactive isotope, most were found to remain within 100 m of their breeding site; the greatest straight line distance travelled being 213 m (Kramer 1973). In another study (Whitaker 1971), all individuals captured in the summer were located within approximately 200 m of potential breeding sites. In Quebec, individuals were caught with drift fences as far as 200 m from the breeding sites (Whiting  2004).

As a precautionary measure, hibernating sites are considered to occur within a 300 m terrestrial zone around breeding wetlands or aquatic features, a zone which must be maintained for the completion of the species’ annual life cycle (Semlitsch and Bodie 2003, Ouellet and Leheurteux 2007).  Although hibernating sites occupy very limited areas, they can be distributed throughout the terrestrial habitat surrounding breeding wetlands or aquatic features.  This terrestrial habitat is generally used from year to year to house Western Chorus Frog hibernating sites.  Accordingly, the terrestrial habitat within 300 m of any wetland or aquatic feature occupied or known to have been occupied by Western Chorus Frog during any life stages is considered to contain at least one occupied residence.  Thus, it is not necessary to confirm the presence or exact location of a hibernating site; this is not advisable since confirming the presence of hibernating sites is also very likely to damage or destroy them.  Only when the habitat no longer exists or the absence of Western Chorus Frog from a specific wetland or aquatic feature has been demonstrated is the area considered to no longer contain a Western Chorus Frog hibernating site.

Damage and Destruction of the Residence

Although the entirety of the terrestrial habitat within 300 m of the occupied wetland or aquatic feature is not considered as being the residence, it is needed to maintain the essential characteristics and function of the hibernating site.  Even though Western Chorus Frogsare freeze-tolerant at subzero temperatures during hibernation (Storey 1990, Storey and Storey 1986, 1987), the hibernating site further protects individuals from freezing. As ectotherms, individuals have limited capacity to respond to disturbance during hibernation, and hibernating sites may be selected to reduce vulnerability to weather events.

Other physiological needs associated with hibernation in Western Chorus Frogs are not very well known, as there is no study published to date focusing on the hibernation physiology of the species, namely because it is excessively difficult to locate hibernating individuals.

To ensure that hibernating sites are available from one year to the next and to maintain the functionality of the hibernating site, the ecological integrity of the terrestrial habitat containing residences must be maintained.  As such, activities which may damage or destroy the hibernating site include those which directly affect the hibernating site as well as those which affect the terrestrial habitat within 300 m of an occupied wetland or aquatic feature and therefore the functionality of the hibernating site.  These latter activities can occur at any time during the year.