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Montana Field Guides

Northern Leopard Frog - Lithobates pipiens

Species of Concern
Native Species

Global Rank: G5
State Rank: S1,S4
(see State Rank Reason below)


Agency Status
USFWS:
USFS: Sensitive - Suspected in Forests (KOOT, LOLO)
BLM: SENSITIVE
FWP SWAP: SGCN1



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Copyright by Canadian Amphibian and Reptile Conservation Network
State Rank Reason (see State Rank above)
Populations within the mountains of western Montana are a Species of Concern with a state rank of S1. Populations on the Great Plains have a state rank of S4 and are not a Species of Concern.
  • Details on Status Ranking and Review
    Northern Leopard Frog (Lithobates pipiens) Conservation Status Review
    Review Date = 05/01/2018
    Range Extent

    ScoreG - 200,000-2,500,000 km squared (about 80,000-1,000,000 square miles)

    Comment280,371 square Kilometers from Natural Heritage Program range maps

    Long-term Trend

    ScoreC - Substantial Decline (decline of 50-75%)

    CommentPopulations west of the continental divide were almost entirely extirpated in the 1970s or 1980s. Declines of 80% were also noted in the central region of the state. Wetlands have declined across the state as well.

    Short-term Trend

    ScoreE - Stable. Population, range, area occupied, and/or number or condition of occurrences unchanged or remaining within ±10% fluctuation

    CommentConsistent detections in eastern and central Montana appear to indicate a stable population within the last 10 years. Some re-introduced populations in western Montana are persisting, however these do not account for more than 10% of historic range.

    Threats

    ScoreF - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.

    CommentApplication of herbicides and pesticides to agricultural lands , general loss of wetlands, ongoing effects of pathogens

    SeverityLow - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.

    CommentSpecies' life history allows them to respond relatively quickly when appropriate habitats are present

    ScopeModerate - 20-60% of total population or area affected

    CommentAs much of the eastern population occurs in or near agriculture there is probably a low level threat to a good portion of occurrences

    ImmediacyHigh - Threat is operational (happening now) or imminent (within a year).

    CommentOngoing

    Intrinsic Vulnerability

    ScoreC - Not Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance; or species has high dispersal capability such that extirpated populations soon become reestablished through natural recolonization (unaided by humans).

    CommentNot intrinsically vulnerable due to high fecundity and relatively low age of maturity.

    Environmental Specificity

    ScoreB - Narrow. Specialist. Specific habitat(s) or other abiotic and/or biotic factors (see above) are used or required by the Element, but these key requirements are common and within the generalized range of the species within the area of interest.

    CommentSpecies relies on riparian areas and lentic or lotic (low flow) waterbodies.

    Raw Conservation Status Score

    Score 3.5 + 0 (geographic distribution) + 0 (environmental specificity) + 0 (short-term trend) + 0 (threats) = 3.5 for all of Montana, S1 west of the Continental Divide

 
General Description
EGGS:
Eggs are laid in a single orange to grapefruit-sized, somewhat flattened globular mass and are usually attached to submerged vegetation. Egg masses are laid individually or communally in groups of up to three dozen egg masses (Nussbaum et al. 1983). Egg masses contain from 645 to 6,272 eggs (X = 3,045, N = 68 for completely counted egg masses at five sites in Colorado and Wyoming) (Corn and Livo 1989). Each ovum is black above, white below, and is surrounded by two jelly layers (Livezey and Wright 1947). Ovum diameters are approximately 1.7 mm (0.07 in), but total egg diameters, including the jelly layers, are approximately 5.0 mm (0.2 in) (Livezey and Wright 1947).

LARVAE:
Body and tail musculature are dark brown to olive or gray with flecks of light gold or silver and black (Bryce Maxell, personal observation). The tail musculature may be pale (Corkran and Thoms 2006). The lateral body surface has a larger proportion of light gold or silver flecks, and the ventral body surface is silvery white to transparent. The tail fin is clear to yellowish with black and light gold or silver flecks and is less than 1.5 times the body length (Bryce Maxell, personal observation). The dorsal tail fin begins anterior to the tail musculature when viewed from the side. The anus is on the right side in front of the fin, not on the midline. The eyes fall within the outline of the head when viewed from above. Lateral oral papillae are strongly indented toward the corners of the mouth, and the lower mandible is noticeably thicker than the upper. (Werner et al. 2004). Tadpoles have a total length of 5.5-100 mm (0.22-3.9 in) (Livo 1981 as cited in Hammerson 1999, Hammerson 1999).

JUVENILES AND ADULTS:
White to cream stripes extend from the tip of the snout laterally underneath the eye to just above the base of the front limb and from just behind each eye to the base of the hind limbs (Bryce Maxell, personal observation). Dorsal base color is either green or brown with large, oval shaped, black spots that are regular in outline and are surrounded with a light halo (Fogleman et al. 1980). Individuals occasionally have a blue to light blue base color (Black 1969a, Hammerson 1999). Ventral color is white to cream with some pinkish patches, especially on the feet. The hind feet have extensive webbing (Bryce Maxell, personal observation) with a snout-vent Length (SVL) of 18-110 mm (0.7-4.3 in) (Nussbaum et al. 1983, Hammerson 1999).

VOICE:
Although both male and female frogs can make croaks, males are typically louder. The mating calls are short (2-3 seconds) and grating sequence of notes with chortles followed by guttural clucking, grunts and squeaks (Werner et al. 2004). Calls are not very loud and can be heard up to a distance of 20 m (65.6 ft) (Bryce Maxell, personal communication).

Diagnostic Characteristics
Adult Columbia Spotted Frogs (Rana luteiventris) often have red or salmon color on their ventral surface. Their dorsal surface has small, irregularly shaped black spots with white or light-yellow centers. Adult Bullfrogs (Lithobates catesbeianus) lack the white to yellowish stripe on the lateral portion of the snout and have tympanums that are the same size or larger than their eye. There is a fold of skin that extends from the back of their eye, over their tympanum, down to their front leg.

Larval Columbia Spotted Frogs have tails that are usually twice their body length with large flecks of black on their body or tail. They often have a metallic copper sheen on the lateral edges of their ventral surfaces. Larvae of the American Bullfrog have a bright to creamy yellow ventral surface with perfectly round black dots on their dorsal surface and tail musculature. The tadpole of this species is much larger in size.
The eggs of Columbia Spotted Frog have diameters approximately twice those of the Northern Leopard Frog because their jelly envelopes are much larger (see descriptions). Additionally, the egg masses of the Columbia Spotted Frog are usually at the water’s surface and not attached to vegetation (Ross et al. 1994b). American Bullfrog eggs are laid in the middle of the summer and are spread out in a thin layer over the surface or bottom of a pond rather than a globular mass.

In Montana, extant populations of Northern Leopard Frog overlap Columbia Spotted Frog and American Bullfrog in very few locations. Northern Leopard Frogs are present mostly across the prairies of the eastern two-thirds of the state while the Columbia Spotted Frog and most American Bullfrog populations are in the mountainous western third. See species accounts for distribution to identify possible regions of co-occurrence.

Species Range
Montana Range Range Descriptions

All Ranges
Native
Historical
(Click legend blocks to view individual ranges)

Western Hemisphere Range

 


Range Comments
The Northern Leopard Frog has a complex taxonomic history but is now recognized as a distinct species that historically ranged from Newfoundland and northern Alberta in the north to the Great Lakes region, the desert Southwest, and the Great Basin in the south (Pace 1974, Dunlap and Platz 1981, Hillis 1988). In addition, a number of isolated populations historically existed in the Pacific Northwest and California (Stebbins 2003). Across this range populations have been documented at elevations up to 3,350 m (11,000 ft) (Hammerson 1999).

In Montana they have historically been documented across the eastern plains and in many of the mountain valleys on both sides of the Continental Divide. Unfortunately, over the last few decades populations of the Northern Leopard Frog have undergone declines and extinctions across much of the western portion of their range (Stebbins and Cohen 1995). Most Northern Leopard Frog populations in western Montana apparently became extinct sometime in the late 1970’s or early 1980’s when virtually no amphibian studies were being conducted in the state. Only two population centers are now known to exist in western Montana, one near Kalispell and one near Eureka (Werner et al. 1998a, Kirwin Werner, Salish Kootenai College, personal communication). In addition, out of 47 historic sites revisited in the mid-1990’s in central Montana, Northern Leopard Frogs were only found at 9 (19%) (Reichel 1995a, 1996, Koch et al. 1996). Populations in southeastern Montana still seem to be widespread and abundant (Reichel 1995b, Hendricks and Reichel 1996b, Koch et al. 1996).

Maximum elevation: 2,042 m (6,700 ft) in Judith Basin County (Maxell et al. 2003).


Observations in Montana Natural Heritage Program Database
Number of Observations: 2848

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Migration
No information on migration of the Northern Leopard Frog is available for Montana. In other locations, Northern Leopard Frogs usually remain in relatively small seasonal home ranges, but may range several hundred meters or more between seasons in the upper Midwest. In Michigan, average nightly movement during rain was 36 m (118 ft), and as much as 800 m (2625 ft). Individuals in Colorado have been documented moving at least 3 km (1.9 mi) between years, and 8 km (5 mi) between-year movements have been reported in the Cypress Hills, Alberta; young-of-the-year moved 2.1 km (1.3 mi) between natal and breeding ponds in the Cypress Hills (Wagner 1997, Hammerson 1999).

Habitat
In Montana, the Northern Leopard Frog is typically found in and adjacent to low elevation and valley bottom ponds, spillway ponds, beaver ponds, stock reservoirs, lakes, creeks, pools in intermittent streams, warm water springs, potholes, and marshes (Brunson and Demaree 1951, Mosimann and Rabb 1952, Black 1969a, Miller 1978, Dood 1980, Reichel 1995a, 1995b Hendricks and Reichel 1996a, 1996b, Hendricks 1999a). Habitats tend to be permanent slow moving or standing water bodies with considerable rooted aquatic vegetation. However, individuals may range widely into moist meadows, grassy woodlands, and even agricultural areas (Nussbaum et al. 1983). In Montana adults are found primarily in riparian habitats or on the prairies near permanent waters without tall dense vegetation (Mosimann and Rabb 1952, Black 1969a, Miller 1978). There is no evidence that this species in Montana has ever occupied high elevation wetlands, in contrast to Wyoming and Colorado (Baxter and Stone 1985, Hammerson 1999).

Northern Leopard Frogs require a mosaic of habitats to meet annual requirements of all life stages. Generally separate sites are used for breeding and overwintering, but this may occur in the same pond in some cases. In summer, adults and juveniles commonly feed in open or semi-open wet meadows and fields with shorter vegetation, usually near the margins of water bodies, and seek cover underwater; taller, denser vegetation seems to be avoided. Adults overwinter on the bottom surface of permanent water bodies, under rubble in streams, or in underground crevices that do not freeze and are well oxygenated (Rand 1950, Emery et al. 1972, Baxter and Stone 1985, Cunjak 1986, Russell and Bauer 1993, Wagner 1997, Hammerson 1999).

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: mtnhp.org/requests) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
Adults feed on a variety of small invertebrates, including various insects, spiders, leeches, and snails obtained along the water's edge or in nearby meadows or fields. but may cannibalize smaller individuals and ingest plant matter incidentally (Knowlton 1944, Moore and Strickland 1954, Whitaker 1961, Linzey 1967, Miller 1975, 1978 Nussbaum et al. 1983, Russell and Bauer 1993, Wagner 1997,). Tadpoles feed on a variety of algae as well as detritus (DeBenedictis 1974). In Montana, adults have been documented feeding on 10 orders of insects, spiders, mites, harvestmen, centipedes, millipedes, snails, and newly metamorphosed Western Toads (Anaxyrus boreas) (Miller 1978), but larval food habits have not been described.

Ecology
Northern Leopard Frogs are active during the day and night. The active period extends from March to November in Colorado (Hammerson 1999). In Wyoming and the Pacific Northwest, adults emerge in March or April (Nussbaum et al. 1983, Baxter and Stone 1985, Russell and Bauer 1993) when water temperatures exceed 10 °C (50 °F). In Montana, the active period of adults is reported to extend from mid-March to early October (Brunson and Demaree 1951, Roedel and Hendricks 1998a, 1998b, Hendricks 1999a). In all cases, activity begins when ice melts.

Adults typically do not move more than 50 m (164 ft) within a seasonal home range but may migrate several hundred to a thousand or more meters between seasonal home ranges (Dumas 1964, Dole 1965a, 1965b, Dole 1967a, 1967b, Dole 1968). Juveniles are known to disperse up to 8.0 km (5 mi) from their natal ponds to their adult seasonal territories (Dole 1971, Seburn et al. 1997).

Predators of adults and juveniles include Great Blue Heron (Ardea herodias), Burrowing Owl (Athene cunicularia), snakes (including gartersnakes), some mammalian carnivores, and game fish. Tadpole predators include Pied-billed Grebe (Podilymbus podiceps), Western Tiger Salamander (Ambystoma mavortium), gartersnakes, and American Bullfrog (Lithobates catesbeianus) tadpoles (Nussbaum et al. 1983, Russell and Bauer 1993, Hammerson 1999). Predators in Montana have not been reported.

Northern Leopard Frogs apparently out-competed Columbia Spotted Frogs at low elevations in Montana (Black 1969a). Differential tadpole mortality may be the primary mechanism of displacement of Columbia Spotted Frog by Northern Leopard Frog (Dumas 1966).

Reproductive Characteristics
Information on reproduction in Montana is limited, and no detailed studies of the reproductive biology of any population have been conducted. Timing appears variable and depends on the year and location. Calling males have been reported in April and May. Near Tiber Reservoir, in Toole and Liberty counties, females have been collected with relatively undeveloped eggs in mid-June and moderately developed to fully developed eggs in early and late July; recently transformed juveniles were also noted in late July (Mosimann and Rabb 1952). Eggs and tadpoles have been reported at breeding sites across eastern Montana during early April to late July, with a peak in May and June; sometimes tadpoles are observed in August and September (Reichel 1995b, Hendricks and Reichel 1996b, Hendricks 1999a, Hossack et al. 2003). Recently metamorphosed juveniles with small tail stubs measured 26-34 mm (1-1.3 in) SVL.

In general, males gather at breeding sites of shallow, quiet water in March to April and vocalize on warm sunny days (water temperatures of 14 to 23 °C (57-73 °F) while floating at the surface of the water. The breeding call of males is a snoring sound lasting 2 to 3 seconds followed by a series of 2 to 3 stuttering croaks or chuckles. In favorable habitat, 20 to 25 or more males may gather in a 20 square meter (65.6 square ft) area.

Females begin laying eggs a few days after calling starts. The time of egg deposition varies with latitude and elevation. Egg deposition occurs typically in April in southern Quebec, New York, and the Great Lakes region, late April to late May farther north in Manitoba and Nova Scotia (Gilbert et al. 1994). In Colorado, eggs are laid mainly in late March or by mid-April at low elevations, and in May in the mountains (Corn and Livo 1989, Hammerson 1999). Females will deposit egg masses singly or communally in waters 7-25 cm (2.8-9.8 in) deep attached to vegetation under the water’s surface in areas well exposed to sunlight (Corn and Livo 1989, Werner and Reichel 1996, Hammerson 1999). Breeding often peaks when water temperatures reach about 10 °C (50 °F). At a particular site, egg deposition generally occurs within a span of about 10 days. Egg masses include several hundred to several thousand ova; the clutch size of 68 Colorado egg masses were 645 to 6272 eggs (Corn and Livo 1989). The density of egg masses often reaches a few hundred per hectare in favorable habitat, sometimes more than 1000 per hectare, but is usually less than 100 in Colorado.

Eggs hatch in about 1 to 2 weeks with hatching taking place over several weeks at a single site. The larval period is about 10 to 12 weeks (58 to 105 days) with recently metamorphosed juveniles documented in late June and early July at lower elevations, and in mid-July to September at higher elevations (Corn 1981, Hammerson 1999). Size at metamorphosis is 21-36 mm (0.8-1.4 in) SVL. Aquatic larvae usually metamorphose in summer, but they may overwinter as tadpoles in some areas (Baxter and Stone 1985). Females are sexually mature usually in two years in most areas, three years in high elevation populations. Breeding males in Colorado are usually more than 5.0 cm (2.0 in) SVL, and breeding females more than 6.0 cm (2.4 in). In northern Minnesota, successful reproduction in acidic bog water either does not occur or is a rare event (Karns 1992).

Management
The following was taken from the Status and Conservation section for the Northern Leopard Frog account in Maxell et al. 2009

Within the last twenty to twenty-five years Northern Leopard Frog populations have declined and been extirpated from large portions of the area from the western plains of Colorado, Wyoming, Montana, and Alberta westward to Oregon and Washington (Roberts 1981, 1987, 1992, Corn and Fogleman 1984, Baxter and Stone 1985, Stebbins and Cohen 1995, Koch et al. 1996, Leonard and McAllister 1996, Leonard et al. 1999, Hammerson 1999). Suggested causes of declines in Northern Leopard Frog populations in this and other areas of the country included loss of wetlands and natural hydrological regimes, introductions of game fish, mosquitofish, and American Bullfrogs, application of pesticides and herbicides, and drought (Roberts 1981, 1987, 1992, Corn and Fogleman 1984, Koch and Peterson 1995, Stebbins and Cohen 1995, Leonard and McAllister 1996, Leonard et al. 1999, Hammerson 1999). While it is likely that all of these factors have played a role in the decline and extirpation of local Northern Leopard Frog populations, many of the declines and extirpations were apparently associated with regional mass mortality events between 1973 and 1982 because declines were observed in relatively pristine areas as well (Roberts 1981, 1987, 1991, 1992, Corn and Fogleman 1984, Koch and Peterson 1995). Reintroduction programs have been initiated in Alberta (Roberts 1991) and have been called for in Washington state (Leonard et al. 1999). The same general timeline for declines is evident in western Montana. Northern Leopard Frog populations were encountered and found to be apparently healthy by a number of masters and doctoral degree students between 1967 and 1977 (Black 1967b, 1970a, Miller 1975, Anderson 1977, Daugherty et al. 1978). A student at the Salish-Kootenai College noted that while he found Northern Leopard Frogs near Kicking Horse Reservoir on the Flathead Indian Reservation during the summer of 1980, local fisherman reported that they had noticed a definite decrease in the number of Northern Leopard Frogs in the area (Ryan 1980). Very little, if any, work was conducted on amphibians in Montana in the 1980s and surveys in the 1990s failed to find Northern Leopard Frogs at any of the historical sites that were revisited and only found two remaining populations in all of western Montana west of the Continental Divide (Werner and Plummer 1995a, 1995b, Werner and Reichel 1994, 1996, Hendricks and Reichel 1996a, Koch et al. 1996, Werner et al. 1998a). Furthermore, while surveys during the 1990’s found them to be common east of the island mountain ranges in eastern Montana, they appeared to have been extirpated from 80% of historic localities on the northwestern plains (Reichel 1995a, 1995b, Hendricks and Reichel 1996a, 1996b Koch et al. 1996, Reichel 1996b, Reichel 1997, Hendricks and Reichel 1998, Rauscher 1998, Roedel and Hendricks 1998a, 1998b, Hendricks 1999a). As a result of these findings the USFS listed the Northern Leopard Frog as a sensitive species in all Region 1 Forests (USDAFS 1999). Risk factors relevant to the viability of populations of this species are likely to include all the risk factors described above. Individual studies that specifically identify risk factors or other issues relevant to the conservation of Northern Leopard Frogs include the following. (1) In conjunction with similar observations for Western Toads (Anaxyrus boreas) Carey (1993) observed the disappearance of two populations of Northern Leopard Frogs in the West Elk Mountains of Colorado between 1974 and 1982. During this period, she found Northern Leopard Frogs with symptoms of red-leg disease, a common bacterial infection in amphibians and fish. She hypothesized that an unidentified environmental factor had caused sublethal stress of both species, which caused immune response to be suppressed, leading to the systemic infection and death. More recently the Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis ), which is suspected to be responsible for declines of amphibians in Australia, Central America, and the western United States, has been found to have caused mass mortalities in Northern Leopard Frog populations in southern Arizona during the summer of 1999 (Berger et al. 1998, Daszak et al. 1999, 2000, Morell 1999, Milius 1999). As was observed for declines in the late 1970’s and early 1980’s only metamorphosed individuals died (Morell 1999). The fungus only seems to attack keratinized tissues, so metamorphosed individuals with lots of keratinized tissues die and tadpoles with keratinized tissues only around the mouthparts survive until metamorphosis (Berger et al. 1998, Morell 1999). Furthermore, it now appears that the Amphibian Chytrid Fungus was responsible for declines in the late 1970’s and early 1980’s as well because museum specimens of Northern Leopard Frogs that were collected during these time period have now been found to have the Amphibian Chytrid Fungus (Carey et al. 1999, Daszak et al. 1999, Milius 2000). Thus, the Amphibian Chytrid Fungus may be the most likely cause of declines of Northern Leopard Frog populations in the western United States and in western Montana in the late 1970’s and early 1980’s and clearly represents a threat to populations today. In support of Carey’s (1993) immunosuppression hypothesis Maniero and Carey (1997) found that Northern Leopard Frogs exposed to low temperatures (5 °C or 41 °F) significantly reduced the animal’s immune response. Thus, Northern Leopard Frogs may be particularly susceptible to the Amphibian Chytrid Fungus or other pathogens when emerging in the early spring or in the late fall or winter or when faced with some other environmental stressor (Carey et al. 1999). (2) Berrill et al. (1993) found that the pyrethroid pesticides permethrin and fenvalerate did not cause significant mortality of embryos when they were exposed to commonly applied levels for 22 to 96 hours. However, tadpole growth and response to a potential predator was delayed following exposure. Berrill et al. (1994) found that the insecticide fenitrothion and the herbicides triclopyr and hexazinone had no effects on embryos, but the fenitrothion and triclopyr did kill or paralyze new hatchlings at concentrations of 2.4 to 4.8 ppm and 4.0 to 8.0 ppm, respectively. Berrill and Bertram (1997) found that northern leopard frog embryos exposed to 6 herbicides (hexazinone, triclopyr ester, triallate, trifluralin, glyphosate, and bromoxynil) and 3 insecticides (permethrin, fenvalerate, and fenitrothion) at levels that are commonly found in areas where they are used on forests or crops in Canada hatched successfully with no unusual mortality. However, when tadpoles were exposed to the same levels, they suffered partial paralysis and the authors note that they would be likely to suffer high rates of mortality. Kaplan and Overpeck (1964) and Kaplan and Glaczenski (1965) found that a variety of organophosphate and halogenated hydrocarbon pesticides caused both red and white blood cell counts to decline in adult Northern Leopard Frogs and chronic exposures to concentrations of 1 ppm caused death in some individuals. Dial and Dial (1987) found that the aquatic herbicides diquat and paraquat did not reduce embryo survival or change hatching time when applied at concentrations of 0.1 to 2.0 ppm. However, at the same concentrations young tadpoles suffered significant mortality from both chemicals and 15-day old tadpoles suffered significant mortality from paraquat. (3) Hecnar (1995) found that acute and chronic toxic effects of ammonium nitrate were observed in Northern Leopard Frog tadpoles at concentrations that are commonly exceeded in agricultural areas. Acute exposures to ammonium nitrate fertilizers at 20 mg/L for 96 hours resulted in 50 percent mortality and significant weight loss in those individuals that survived. Chronic exposures to 10 mg/L for 100 days resulted in significantly lower survivorship. Cameron (1940) found that well water containing 1 ppm flourine caused embryo development to slow and time to hatching to decrease. Lande and Guttman (1973) found that embryos were not affected by copper sulfate at concentrations up to 1.56 mg/liter of copper, but the LD50 for tadpoles was 0.15 mg/liter and tadpole growth rates were decreased at concentrations of 0.06. (4) Hamilton (1941) found that rotenone applied at 0.1 mg/L caused mortality in larval through metamorphic life history stages of Northern Leopard Frogs over an 8- to 24-hour time period, respectively. Furthermore, Burress (1982) found that Pro-Noxfish applied at 5 µL/L caused substantial mortality in Northern Leopard Frogs. (5) Black (1969a) felt that exotic American Bullfrogs introduced in the Bitterroot Valley had led to declines in Northern Leopard Frog populations in the area. Similarly, Hammerson (1982) documented a decline in the abundance of Northern Leopard Frogs as American Bullfrog numbers increased at a site in Colorado. (6) Vatnick et al. (1999) found that adult Northern Leopard Frogs preferred a neutral pH in a choice test and found that when they were exposed to water of pH 5.5 for 10 days, they suffered 72% mortality while those exposed to a pH of 7.0 suffered only 3.5% mortality. Furthermore, frogs appeared to be much more sensitive to low pH immediately after emergence from hibernation. Those exposed to a pH of 5.5 immediately after emerging all died within 4 days while frogs exposed after they had completed breeding activities only suffered 58% mortality over a 10-day period. Freda et al. (1991) report that a pH below 4.6 causes mortality of embryos to increase significantly from controls and all embryos die when exposed to a pH of 4.2-4.5. Corn and Vertucci (1992) report an LC50 of embryos at a pH of 4.5. Freda and Dunson (1985) found that tadpoles raised at a pH of 4.4 grew slower than siblings raised at a pH of 5.8. Furthermore, older tadpoles had higher survival rates at low pH than younger tadpoles. Schlicter (1981) found that sperm motility decreased below pH 6.5 and no embryos survived below a pH of 4.8. Long et al. (1995) found that low pH and UV-B acted synergistically to cause mortality in Northern Leopard Frog embryos. Freda et al. (1990) found that at a pH below 4.8, aluminum complexed with dissolved organic carbon and became toxic to tadpoles. (7) Nash et al. (1970) found that loud noises resulted in an immobility reaction in Northern Leopard Frogs. This could leave them at greater risk of mortality from traffic or heavy machinery. (8) Ankley et al. (2000) found that limb deformities were more prevalent when tadpoles were exposed to higher levels of UV-B radiation.

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    • Wetlands West, Inc., Bozeman, MT., and Land & Water Consulting, Inc., Missoula, MT., 2002, Montana Dept. of Transportation Wetland Mitigation Monitoring Report, Year 2001: Wyola-Sunlight Ranch Wetland, Wyola, Montana. Proj. No. 130091.035. July 2002. In 2001 Wetland Mitigation Monitoring Reports, Vol. II.
    • Wheeler, G.C. and J. Wheeler. 1966. The amphibians and reptiles of North Dakota. University of North Dakota, Grand Forks, ND. 104 pp.
    • Wied, M.P. 1843. Travels in the interior of North America by Maximilian, Prince of Wied. With numerous engravings on wood, and a large map. Translated from the German by H. Evans Lloyd. To accompany the original series of eighty-one elaborately-coloured plates. Size, imperial folio. Ackerman and Co., London, England. 520 p.
    • Wied, M.P. 1865. Verzeichniss der reptilien, welche auf einer reise in nordlichen America beobachtet wurden, von Maximilian, Prinzen zu Wied. Eigengangen bei der Akademie am 1, Juni 1865. Druck von E. Blochmann und Sohn, Dresden, Germany. 141 p.
    • Wojtaszek, B.F., T.M. Buscarini, D.T. Chartrand, G.R. Stephenson, and D.G. Thompson. 2005. Effect of Release herbicide on mortality, avoidance response, and growth of amphibian larvae in two forest wetlands. Environmental Toxicology and Chemistry 24(10):2533-2544.
    • Wolff, J.B., M.J. Lee, and C.W. Anderson. 2004. Contribution of the submentalis muscle to feeding mechanics in the leopard frog, Rana pipiens. Journal of Experimental Zoology 301A(8):666-673.
    • Yaremko, L. 1994. Northern leopard frog project- field report 1994. Unpublished Report For Fish and Wildlife Services, Edmonton, AB. 85pp.
    • Yarrow, H.C. 1882. Check list of North American reptilia and batrachia, with catalogue of specimens in the U.S. National Museum. United States National Museum Bulletin 24. 249 p.
    • Zenisek, C.J. 1963. A study of the natural history and ecology of the leopard frog, Rana pipiens (Schreber). Ph.D. dissertation, Ohio State University, Columbus, Ohio. 153 pp.
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Northern Leopard Frog — Lithobates pipiens.  Montana Field Guide.  .  Retrieved on , from