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).
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; StHilaire 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 Frogs are 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.