AMPHIBIANS RE-EVALUATION OF RELATIVE ABUNDANCE OF FIVE FROG AND TOAD SPECIES IN RIDING MOUNTAIN NATIONAL PARK, MANITOBA Ken Kingdon
Riding Mountain National Park, Wasagaming, MB, R0J 1N0. E-mail:
Introduction Canadian toad, as it was believed to My personal observations have be extirpated at least 20 years before suggested that there may have been the current study. A brief comparison several changes in the frog and toad to changes in amphibian populations populations and their distribution within in other areas around RMNP was also Riding Mountain National Park (RMNP), made. MB. A 1974 checklist identified the following species as occurring in RMNP: Materials and Methods Canadian toad (Anaxyrus hemiophrys), Historic information on frog relative gray treefrog (Hyla versicolor), boreal densities was gleaned from the RMNP chorus frog (Pseudacris maculata), wood library. To assess current relative frog (Lithobates sylvaticus), and northern abundance of frogs inside RMNP, visual leopard frog (Lithobates pipiens).1 and calling surveys were carried out in a According to the Canadian Amphibian manner set out by Kendell,4 and the result and Reptile Conservation Network compared with historic information.1,5 The (CARCNET), this is the generally expected survey period was from April to October distribution of frogs and toads for the 2010, which encompassed breeding/ region.2 However, significant worldwide reproduction periods, metamorphosis, changes in amphibian populations have and movement of frogs to their wintering been noted for at least 35 years, and sites in the fall. Surveys were conducted regionally, the northern leopard frog has at different times of day to permit detection declined in large areas of its original range during both visual surveys and calling in North America.3,4 surveys.
The objective of this study was to Visual Surveys: Two different types compare changes in abundance of frog of visual surveys were conducted. First, and toad species in RMNP to two previous seven permanent routes were established estimates of relative abundance made in (Fig. 1) to survey areas where leopard 1974 and 1987.1,5 Due to large perceived frogs had previously been detected in changes in northern leopard frog and gray the last 15 years.6,7 Each of the seven treefrog populations, special emphasis permanent routes was surveyed at was placed on changes in these two least five times, with three of the most species. On the other hand, no special accessible routes surveyed nine times. measures were made to assess the Second, 30 trails/routes were also
168 Blue Jay Figure 1. Location of seven permanent survey routes in Riding Mountain National Park, MB.
69 (4) December 2011 169 surveyed opportunistically during the correspond with expected calling periods daytime in July, August, and September of wood frog (April, early May); boreal using the same method. chorus frog, leopard frog, and Canadian toad (May); and gray treefrog (June). It is Surveyors moved slowly around the recognized that species’ calling periods perimeter of each pond (in the case of overlap, but the survey was designed permanent routes) or along trails (in the to ensure maximum potential to record case of opportunistic routes) searching presence of all five expected species. Call approximately 1 m to each side or in rates were also recorded at other times front for frogs visible without moving of the day, and also along opportunistic debris. Both the pond edge and upland survey routes where applicable. areas were surveyed. All egg masses, tadpoles, young-of-the-year, and adults Results observed were recorded on datasheets. Historic Information: The review of the To increase the ability to spot frogs, historic information provided a baseline visual surveys were conducted during of relative abundance of frog and toad the warmest period of the day, usually species. While much of the information on after noon, when amphibian activity how the lists were developed was missing, was expected to be greatest.4 Travel the definitions used to establish densities speed was adjusted slightly depending were useful, and these definitions were on the terrain so that surveyors were also used to compare the 2010 results to confident that all amphibians in sight previous surveys. Results of research into were observed. The date, start time, end historic abundance are presented in Table time, air temperature, transect length, 1, as a tabular comparison of a previous and pond location were recorded for each checklist (1974) and survey (1987).1,5 survey. The survey transect length was calculated by recording the route on a 2010 Relative Abundance Surveys: The hand-held GPS unit (Garmin 60 Cx). The average length of the permanent surveys UTM coordinates were recorded for each was 1.16 km, and the surveyor’s average pond/route. survey speed was 2.06 km/h, while the average length of the opportunistic Call Surveys: 2010 nocturnal call surveys was 5.77 km and the average surveys were also conducted as outlined survey speed was 4.89 km/h. Wood frogs, by Kendell.4 On each of the permanent boreal chorus frogs, and gray treefrogs routes, an estimate of the abundance were detected at least once on all seven of each calling species heard was permanent routes, while northern leopard recorded during a 3-min survey period. frogs were found on three of the routes, The abundance of calling frogs was and Canadian toads on 0 routes (Table estimated using four calling codes: no 2). Gray treefrogs were detected on males calling was coded as “0,” individual nearly one-third of the surveys, providing males calling with no overlap were coded evidence of a large increase in the range as “1,” individual males calling with some and population of this species within overlap of calls were coded as “2,” and a RMNP. full chorus, with no discernable individual calls, was coded as “3.” The surveys Visual sightings of metamorphosed were conducted at least a half hour after individuals including young-of-the-year, sunset and ended before midnight. The sub-adults, or adults of wood frogs and call surveys were conducted at several northern leopard frogs were compared different times during the spring to for the seven permanent routes (Table
170 Blue Jay Table 1. Results of frog and toad abundance from 1974, 1987, and 2010, with (a) a comparison of 2010 survey results to previous 1974 checklist/1987 survey, and (b) newly developed abundance definitions.
(a) Comparison of survey results
Species 1974 2010 results 1987 2010 results 2010 results abundancea using 1974 abundanceb using 1987 using new definitions definitions definitionsc Canadian toad Common ? Rare ? Extirpated Gray treefrog Rare Common Uncommon Common Common Boreal chorus frog Abundant Abundant Common Common Abundant Wood frog Common Abundant Common Common Abundant Northern leopard Abundant Uncommon Common Uncommon Uncommon frog
(b) Definitions of frog and toad abundance
Term a1974 definition b1987 definition c2010 definition Abundant Seen on almost all Seen or heard daily on all visits to the preferred visits to appropriate habitat habitat during the proper during the appropriate seasons. seasons. Common Seen on a majority of Likely to be seen daily in the Seen or heard on greater visits to the preferred park in appropriate habitat than 50% of visits to habitat during the proper during the appropriate appropriate habitat during seasons. season. the appropriate seasons. Uncommon Present every year in the Sparsely distributed. May Seen or heard on <50%, preferred habitat during be seen in appropriate but >10%, of visits to the proper seasons, but habitat during the appropriate habitat during occurs in low numbers appropriate season but the appropriate seasons; and often difficult to not on a daily basis. occurs in low numbers, find. exhibits sparse distribution. Rare Present every year but in Present in low numbers Believed to be present in low numbers at varying and/or sparsely distributed. the park, seen or heard on locations. May be seen only <10% of visits to appropriate occasionally. habitat during the appropriate seasons. Detected in low numbers and very limited distribution. Not necessarily seen or heard every year. Extirpated No longer found in the park.
69 (4) December 2011 171 3). On these seven routes, a total of 315 checklist and the 1987 survey results, wood frogs were observed, compared to using the definitions of abundance used in only seven leopard frogs, suggesting that 1974 and 1987, respectively (Table 2). wood frogs were much more abundant than leopard frogs. As comparisons between the three surveys were conducted, it became On the opportunistic routes, wood frogs apparent that a more quantitative set were also the most abundant species of definitions was needed. A new set of observed, followed in order of decreasing definitions for frog and toad abundance abundance by boreal chorus frogs, was created, based on some of the leopard frogs, and gray treefrogs (Table previous definitions used in the 1974 4). No Canadian toads were observed. checklist and the 1987 amphibian survey. Tables 2 and 4 show consistent detection Even these new definitions create some rates for wood frogs and leopard frogs on problems with interpretation of what both permanent and opportunistic survey exactly is meant by “in appropriate habitat routes, while there was a decrease in in the appropriate season.” Thus, while the detection rate of boreal chorus frogs all of RMNP’s ecosystems are generally and gray treefrogs on the opportunistic considered to support all expected species surveys compared to the permanent (i.e. almost all areas inside the park could routes. be considered appropriate habitat for all species), the appropriate season is more Discussion difficult to determine. Enhancement of Using the methodologies outlined the definition of “appropriate season” above, it is impossible to make definitive is recommended, based on life cycle/ statements about the relative abundance behavioural characteristics of each or true abundance of amphibians in species (Table 5).2,10 Table 5 identifies RMNP. As discussed in previous studies, the recommended survey technique and there are several weaknesses related to appropriate season by month for each a survey that combines both qualitative species. and quantitative data, particularly one in which the survey areas were non- This refinement of the definition of randomly selected, and the entire area “appropriate season” is also useful as was not surveyed.8,9 In addition, the it recognizes differences among the majority of the surveys were conducted species which affect numbers detected. in a relatively haphazard manner, which Gray treefrogs and boreal chorus frogs allows the development of a species are difficult to see in visual surveys. list, but makes replication for monitoring Wood frogs and northern leopard frogs purposes impossible.9 are much more terrestrial and larger, making visual observations easier in July However, there is little doubt that and August. Nocturnal call surveys are there have been changes in the frog and useful for estimating abundance of wood toad populations within RMNP. When frogs, but quieter, less vocal species such comparing the 2010 results to those as leopard frogs are not as effectively from 1974 and 1987, a definite decline found by their calls.4 Detecting egg in both northern leopard frogs and masses is also difficult for some species, Canadian toads is evident, while gray including gray treefrogs. Thus, an effort treefrog populations have increased. To was made to determine the abundance examine the changes further, the 2010 of each species by using the appropriate survey results were compared to the 1974 survey methodology. Climate change may
172 Blue Jay Table 2. Number of surveys of the seven permanent routes on which each species was observed. In total, 48 surveys were conducted in 2010. Species No. of surveys (% of all surveys) Canadian toad 0 (0) Gray treefrog 15 (31.3) Boreal chorus frog 20 (41.7) Wood frog 28 (58.3) Northern leopard frog 6 (12.5)
Table 3. Comparison of survey results on seven permanent routes for wood frog and northern leopard frog. In total, 48 surveys were conducted. Wood frog Northern leopard frog Total no. of individuals observed 315 7 No. of routes observed (% of all routes) 25 (52.1) 6 (12.5) No. of individuals observed/hour 11.62 0.26 No. of individuals observed/km 5.64 0.13
Table 4. Comparison of survey results on 30 opportunistic survey routes for each species observed. Canadian Gray Boreal Wood frog Northern toad treefrog chorus frog leopard frog No. of individuals 0 3 33 253 23 % of routes detected 0 6.7 33.0 53.3 10 No. of individuals/hour 0 0.09 0.93 7.13 0.65 No. of individuals/km 0 0.02 0.19 1.46 0.13 require further adjustment of “appropriate gray treefrogs inside RMNP in 1995, season” for species where the onset in the town of Wasagaming within the of the breeding season is determined central portion of the park, an area at primarily by temperature rather than by that time considered to be outside the photoperiod. normal range of this species. Since that time, I have detected gray treefrogs in As stated, gray treefrogs were detected all regions of the park, including in the on all seven permanent routes during highest elevations of the eastern portion the call surveys. According to both the and in the driest prairie regions. They 1974 checklist and previous work, gray have also been found in the most westerly treefrogs were present, but considered areas of the park, approximately 50 km uncommon in RMNP.1,10 According to beyond the historic range of the species. published maps, treefrogs appeared to This includes a dead specimen that I be confined to the eastern portion of the discovered in a cabin at the Sugarloaf Park, and were still considered to be trailhead on 28 October 2010, near uncommon in 1987. 5,10,11 I first observed the western boundary of RMNP. Taylor
69 (4) December 2011 173 also recorded a possible change in the wood frog visual detections on both distribution of gray treefrogs in western the seven permanent routes and the Manitoba outside the park, although opportunistic surveys. As previously he indicated that this apparent range stated, the permanent routes were extension may be a function of historic selected based on relatively recent under-sampling of these areas.12,13 observations of leopard frogs in the However, this is not the case in RMNP, immediate area. Therefore, even though which was well surveyed in the past, yet the routes were biased towards leopard has shown an increase in population frog detections, the results in Table 3, density and distribution from the 1987 supported by the data presented in Table survey to the 2010 survey. 4, indicate that leopard frogs are currently found less often than wood frogs. Thus, The comparison of detection rates of there is solid evidence that the leopard frog species between permanent routes frog population has declined both in and the opportunistic routes provides abundance relative to wood frogs and, some food for thought. Boreal chorus based on the 1974 checklist and 1987 frogs may have been observed less survey definitions, also in actual numbers. frequently on the opportunistic surveys The other alarming note is the apparent when compared to the permanent routes extirpation of Canadian toads from the due to the relatively faster average speed park since 1987. during the former, making it difficult to observe the small frogs. Several possible reasons could account for these changes in leopard frog and As well, the detection rates reported Canadian toad populations. Collins in Table 4 for northern leopard frogs and and the CARCNET website provide gray treefrogs are misleading. It would good reviews of possible causes of frog appear that the opportunistic surveys and toad declines around the world, were better at finding leopard frogs, ranging from climate change, changes and that these frogs are more common to water quality, acid rain, and increase than the treefrogs. It should be noted, in ultraviolet light, to habitat destruction, however, that 20 of the 23 leopard frog competition, commercial harvesting, sightings were from one site that I visited and disease.2,3 Several of the expected as a direct consequence of park staff causes do not appear to apply to RMNP. observations of this group of frogs. As For example, commercial harvesting has well, as stated above, gray treefrogs are never been allowed in the park. Research extremely difficult to detect when they are on the effects of the reintroduction of not calling. Most opportunistic surveys beavers on the park ecosystem has were done later in the summer, after the shown that the area of park surface water breeding period, and thus detections were has actually increased between1964 and primarily visual observations. The only 1996 due to impounded water, suggesting gray treefrog detections were of calling that habitat loss is not a key factor in frog males in August, outside the normal declines.14 breeding season. Whenever discussion occurs regarding Given the analysis above, there have fluctuations in populations, climate been definite declines in two species, change is often highlighted as a possible namely the Canadian toad and the reason for the differences. Amphibians northern leopard frog. Further analysis may be particularly sensitive to long- was done to compare leopard frog and term changes in the weather. It is too
174 Blue Jay Table 5. Recommended survey time and method for monitoring five species of frogs and toads in Riding Mountain National Park, MB. April May June July August September Canadian Nocturnal Visual toad call survey search for tadpoles Gray Nocturnal Nocturnal Nocturnal Visual treefrog call survey call survey call survey, search for (mid- to end visual tadpoles of month) search for tadpoles Boreal Nocturnal Nocturnal Visual Visual Visual chorus frog call survey call survey search for search for search for tadpoles tadpoles & dispersing dispersing frogs to young of over- year wintering areas Wood frog Nocturnal Nocturnal Visual Visual Visual call survey call survey search for search for search for tadpoles tadpoles dispersing dispersing frogs to young of over- year, & wintering adults areas Northern Incidental Incidental Visual Visual Visual leopard nocturnal nocturnal search for search for search for frog call survey call survey tadpoles dispersing dispersing (conducted (conducted young of frogs to while while year & over- surveying surveying adults wintering other other areas species) species) early to determine whether the changes could possibly play a role in the decline observed in this study can be attributed to of leopard frogs and the disappearance a warming climate. However, as in most of the toads, as warmer temperatures areas on the prairies, some changes in could result in ponds drying up prior to weather have been noticed in the Riding successful metamorphosis of tadpoles, Mountain area. In particular, weather and thus increased mortality. data from the Environment Canada weather station in Wasagaming does The slight increase in mean annual show a slight overall warming in annual temperatures and an increase in the temperature since the 1970s.15 As well, coldest winter temperature could provide the mean annual minimal temperature one explanation for the apparent increase also appears to be increasing, indicating of gray treefrogs in the park. This species a general warming trend. These changes mates at warmer temperatures and
69 (4) December 2011 175 later in the spring than other resident not uniform, however, and some localized frogs and toads, and an increase in leopard frog populations appear to be summer temperatures may provide more able to persist, despite an apparently opportunities for breeding.16 The warmer decreasing regional population.19,20 annual minimal temperatures may also mean that more gray treefrogs overwinter What, then, is the current status of successfully, particularly during low-snow northern leopard frog populations in years when severe cold would normally RMNP? The decline appears to have penetrate into the leaf litter. Relative been slower than observed in areas humidity and elevation have been outside the park, but may be still in suggested as possible limiting factors progress. Again anecdotally, I observed in the distribution of gray treefrogs.10,12 leopard frogs relatively frequently prior to However, as stated, this species has 2005. Since that time, leopard frogs have now been heard in all areas of the park, been found less often, despite numerous including both the highest elevations and revisits to the areas where they had the driest areas. This may indicate that previously been observed. However, the the distribution of gray treefrogs is no fact that they can still be found in a variety longer limited by either of these historic of areas of the park suggests that the factors due to changes in local weather. population will persist for the time being. Whatever the reasons for the changes in RMNP frog and toad populations, Conclusion and Recommendations their beginnings can likely be dated back As discussed above, while the to the 1970s, based on much earlier methodologies do not allow us to observations near the park and my own determine actual population sizes, the subsequent observations. Bird reported information garnered from this survey that historically, leopard frog densities does allow several conclusions to be reached highs of 194 individuals per drawn. acre in the Parkland region.17 His field station was located near Birtle, Manitoba, The first is that this survey has confirmed approximately 50 km from the RMNP the trend first observed in 1987, in which it boundary. Densities at the field station appears that Canadian toad populations are expected to have been similar to the have declined such that they are now surrounding aspen parkland, including considered to be extirpated from the park. similar habitat inside the park. It also confirms my personal observations that northern leopard frogs have declined Anecdotally, as a child raised on a farm in abundance, but these populations do in the 1970s in an area approximately 50 not appear to be imminently threatened km south of the park, I noted a sudden with extirpation. Finally, the survey also decline in leopard frogs. By 1980, they confirms the expansion of both the range were rarely found on our farm, while a and the abundance of gray treefrogs decade earlier, they had been abundant. inside the park since 1987. They have since become extirpated from the farm. These observations coincide The following recommendations are with observations in Alberta, where suggested to provide further insight into leopard frogs declined suddenly in the the findings of this survey: late 1970s and early 1980s.18 These records point to a widespread and 1. Following the completion of a review of catastrophic decrease in the Canadian the park’s lake water quality, any changes prairie populations. This decrease was in the physical and chemical makeup of
176 Blue Jay RMNP water bodies should be examined 7. Forsyth D (2002) Amphibian Monitoring to Detect for their possible negative effects on local Malformations in Newly Metamorphosed Frogs. Canadian Wildlife Service, Environment Canada, frog or toad populations. Edmonton, AB.
2. Following the development of 8. Heyer WR, Donnelly MA, McDiarmid RW, Hayek LC, Foster MS (1994) Measuring and standardized survey methods, amphibians Monitoring Biological Diversity - Standard Methods in the park should be monitored every five for Amphibians. Smithsonian Institution Press, years, starting in 2015. Washington, DC.
9. Dodd, CK (ed) (2009) Amphibian Ecology and 3. A multi-jurisdictional study of the current Conservation: A Handbook of Techniques. Oxford Canadian toad population abundance University Press, Oxford. and distribution across western Canada 10. Preston WB (1982) The Amphibians and Reptiles should be carried out to determine of Manitoba. Manitoba Museum of Man and Nature, whether the apparent declines in RMNP Winnipeg, MB. are reflected in other areas. 11. Cook FR (1984) Introduction to Canadian Amphibians and Reptiles. National Museums of Acknowledgments Canada, Ottawa, ON. I thank the RMNP staff for their frog sightings, and for making my return to 12. Taylor P (2008) Northward range extension for the gray treefrog in west-central Manitoba. Blue Jay university possible. Thanks also to D. 66:44-49. Schock, P. Taylor, L. Thorpe, and M. Vassal, and an anonymous reviewer who 13. Taylor P (2009) An extension of treefrog range reviewed early versions of this paper. in Manitoba and into Saskatchewan. Blue Jay 67:235-241. Finally, I thank Rae, Katrien, Rebecca, and Abbey for their patience. 14. Sinkins P (2008) Ecological and hydrological consequences of beaver activity in Riding Mountain 1. Anonymous (1974) List of Reptiles and Amphibians, National Park, Manitoba. M.Sc. Thesis, University of Riding Mountain National Park. Indian and Northern Manitoba, Winnipeg, MB. Affairs, Catalogue No. R63-9874, Information Canada, Ottawa, ON. 15. Environment Canada Weather Data. Available at
4. Kendell K (2002) Survey Protocol for the Northern 17. Bird R (1930) Biotic communities of the aspen Leopard Frog. Alberta Sustainable Resource parkland in central Canada. Ecology 11: 356-442. Development, Fish and Wildlife Division, Alberta Species at Risk Report No. 43, Edmonton, AB. 18. Alberta Northern Leopard Frog Recovery Team (2005) Alberta Northern Leopard Frog Recovery Plan, 5. Munro SL (1987) Herpetile Field Survey Data 2005–2010. Alberta Species at Risk Recovery Plan Report, Riding Mountain National Park. Natural No 7. Fish and Wildlife Division, Alberta Sustainable Resource Conservation, Prairie and Northern Region, Resource Development, Edmonton, AB. Environment Canada. Winnipeg, MB. 19. Bailey M (2004) Northern leopard frogs in a golf 6. Rempell J (2001) Recommendations for assessing course water hazard. Blue Jay 62:43-45. northern leopard frog (Rana pipiens) populations within Riding Mountain National Park. Unpublished 20. Schock DM, Bollinger TK (2005) An apparent document, Brandon University, Brandon, MB. decline of northern leopard frogs (Rana pipiens) on the Rafferty Dam mitigation lands near Estevan, SK. Blue Jay 63:144-154.
69 (4) December 2011 177