Montana Field Guide

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).

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.

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).

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).

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.

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).

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).

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.