Montana Field Guide

Western Toad - Bufo boreas

The skin of adult boreal toads is covered with small round or oval warts on a background color that is usually green or brown; the warts may be reddish-brown and encircled by dark pigment. Parotoid glands are oval and larger than the eyes, cranial crests are absent or indistinct. The eyes have horizontal pupils. Usually there is a light stripe down the middle of the back, but this may be absent or inconspicuous in juveniles. The underside of each hind foot has two brown tubercles that lack sharp cutting edges. Mature males have a dark patch on the inner surface of the innermost digit ("thumb") during breeding. Males lack a vocal sac, however, they may produce a repeated chirping sound. Males rarely exceed 9.5 centimeters snout-vent length (SVL), females rarely 11.0 centimeters.

The body and tail of tadpoles is black or dark brown, with the eyes about midway between the dorsal midline and edge of the head. Labial tooth rows are 2/3, oral papillae are restricted to the sides of the mouth, and the anus is on the midline at the front end of the ventral tail fin; maximum total length is about 3.5 centimeters. The eggs are black, about 1.5 to 1.8 millimeters diameter, and are laid in long 5 millimeters-wide strings of double-layered jelly in two rows (sometimes one or three) that appear to be a single zigzag row.

Adult boreal toads lack the prominent cranial crests found on the other species of Montana toads, and have horizontal rather than vertical pupils, as is present in the plains spadefoot. Boreal toad tadpoles lack visible white or gold flecks on the back that are present in Woodhouse's and Great Plains toad tadpoles. Woodhouse's toad ova are enclosed in a single jelly layer, not two, and Great Plains toad eggs are in strings that are noticeably pinched between each egg. However, eggs and tadpoles of boreal and Woodhouse's toads are very similar and may be indistinguishable in some cases. Distribution is a useful character for all life stages, as the range and habitat of the boreal toad do not overlap any other toad in Montana, with the possible exception of Woodhouse's toad (Bufo woodhousii) in a very narrow area north of the Beartooth and Absaroka mountains (Maxell et al. 2003).

Montana Range

No information is available specific to Montana. Elsewhere is it known that the boreal toad migrates between aquatic breeding and terrestrial nonbreeding habitats. In Colorado, movements of 900 meters (with 95 meters change in elevation) to 4 kilometers have been reported (Hammerson 1999), and radio-tracked females in Idaho have been observed to move up to 2.4 kilometers from breeding ponds (Koch and Peterson 1995). Movement patterns are highly variable, with some individuals remaining in the same location for several days, then moving 50 meters or more on several consecutive nights.

Habitats used by boreal toads in Montana are similar to those reported for other regions, and include low elevation beaver ponds, reservoirs, streams, marshes, lake shores, potholes, wet meadows, and marshes, to high elevation ponds, fens, and tarns at or near treeline (Rodgers and Jellison 1942, Brunson and Demaree 1951, Miller 1978, Marnell 1997, Werner et al. 1998, Boundy 2001). Forest cover in or near encounter sites is often unreported, but toads have been noted in open-canopy ponderosa pine woodlands and closed-canopy dry conifer forest in Sanders County (Boundy 2001), willow wetland thickets and aspen stands bordering Engelmann spruce stands in Beaverhead County (Jean et al. 2002), and mixed ponderosa pine/cottonwood/willow sites or Douglas-fir/ponderosa pine forest in Ravalli and Missoula counties (P. Hendricks personal observation).

Elsewhere the boreal toad is known to utilize a wide variety of habitats, including desert springs and streams, meadows and woodlands, mountain wetlands, beaver ponds, marshes, ditches, and backwater channels of rivers where they prefer shallow areas with mud bottoms (Nussbaum et al. 1983, Baxter and Stone 1985, Russell and Bauer 1993, Koch and Peterson 1995, Hammerson 1999). Forest cover around occupied montane wetlands may include aspen, Douglas-fir, lodgepole pine, Engelmann spruce, and subalpine fir; in local situations it may also be found in ponderosa pine forest. They also occur in urban settings, sometimes congregating under streetlights at night to feed on insects (Hammerson 1999, P. Hendricks personal observation). Normally they remain fairly close to ponds, lakes, reservoirs, and slow-moving rivers and streams during the day, but may range widely at night. Eggs and larvae develop in still, shallow areas of ponds, lakes, or reservoirs or in pools of slow-moving streams, often where there is sparse emergent vegetation. Adult and juvenile boreal toads dig burrows in loose soil or use burrows of small mammals, or occupy shallow shelters under logs or rocks. At least some toads hibernate in terrestrial burrows or cavities, apparently where conditions prevent freezing (Nussbaum et al. 1983, Koch and Peterson 1995, Hammerson 1999).

The diet of Montana adults includes five insect orders; spiders, daddy longlegs, and millipeds (Miller 1978), with ants and ground beetles as common items.

Research outside the state shows that metamorphosed individuals feed on various small invertebrates, including seven orders of flying insects, spiders, mites, daddy longlegs, snails, crayfish, sowbugs (terrestrial amphipods), and earthworms (Nussbaum et al. 1983, Hammerson 1999); larvae filter suspended plant material or feed on bottom detritus.

Basking groups of up to 1000 young-of-year have been observed in Waterton National Park; basking sites may be important at high elevations (Black and Black 1969). They are active day/evening in early summer and late evening/night when it's hot (e.g. August) (Miller 1975).

Generally, boreal toads are active during the day and night; juveniles are largely diurnal while adults tend to be nocturnal except in spring (Maxell 2000). The active period typically begins in April or May and extends to September or October, depending on elevation and latitude (Russell and Bauer 1993, Koch and Peterson 1995, Hammerson 1999), although adults may be active in January and February in coastal populations (Nussbaum et al. 1983). In Montana, records extend from late April to early October (Rodgers and Jellison 1942, Brunson and Demaree 1951, Black and Brunson 1971, Hendricks and Reichel 1996, Boundy 2001).

Predators of adult toads include raccoon, domestic dog, coyote, red fox, short-tailed weasel, mink, marten, badger, black bear, Northern Pygmy Owl, Black-billed Magpie, Common Raven, American Crow, Steller's Jay, Gray Jay, American Robin, Loggerhead Shrike, and Northern Shrike (Salt 1979, Olson 1989, Corn 1993, Brothers 1994, Koch and Peterson 1995, Hammerson 1999, Jones et al. 1999). Predators of toad tadpoles include Mallard, Spotted Sandpiper, western terrestrial garter snake, tiger salamander, wood frog tadpoles, and diving beetle larvae. Predators of boreal toad in Montana are not documented.

The reproductive biology of boreal toads in Montana is poorly described. The breeding period extends from April to mid-July; breeding aggregations of more than 40 adult males have been reported in mid-May (Black and Brunson 1971). Eggs are laid from early May to late June, tadpoles are present from late May to early September, and recently metamorphosed toadlets have been reported from early June to late August (Brunson and Demaree 1951, Werner and Reichel 1994, Reichel 1995, Hendricks and Reichel 1996, Marnell 1997, Boundy 2001, Burton et al. 2002). Size of one clutch in the Bitterroot Valley of Ravalli County was 20,000 eggs; eggs were laid in late May and produced metamorphosed toadlets by July 11, about 40 to 49 days after oviposition (Maxell et al. 2002).

In other areas of the species' range, the breeding period is known to be variable depending on location; in the mountains it follows the melt of winter snowpack, and in some cases eggs may be laid when ponds are still rimmed with ice. Water temperature may be as low as 7.5 but usually more than 9.0 (Salt 1979). At a given site, breeding may extend over several weeks, although a peak usually occurs.

Breeding aggregations may be quite large (more than 2000 adults), but most often are much smaller, with males outnumbering females. Eggs are laid in two jelly strings usually in shallow water often no more than 15 centimeters deep, and often are deposited in the open with little vegetation cover. Typical clutches in Colorado contain 3000 to 9000 eggs (mean of 5200 eggs), although in the Pacific Northwest clutches of 12,000 eggs are considered normal, and may reach 16,000 eggs (Nussbaum et al. 1983, Koch and Peterson 1995, Hammerson 1999). Eggs hatch in 3 to 12 days. Tadpoles are about 1.0 centimeter total length at hatching and grow to about 2.5 to 3.0 centimeters. They sometimes are found in huge aggregations; one in Yellowstone National Park, Wyoming measured 0.5 meter wide and more than 36 meters long, and another in the Oregon Cascades was 1.0 meter wide by 300 meters long (Nussbaum et al. 1983, Koch and Peterson 1995).

Tadpoles metamorphose in first summer and take two months or more to reach metamorphosis, depending on the water temperature. At high elevation sites near treeline in Wyoming and Colorado tadpoles may fail to metamorphose (Baxter and Stone 1985, Hammerson 1999), and persistence of these populations may be dependent on immigration of juveniles and adults from lower elevation; overwintering of tadpoles has never been observed. Metamorphosis usually occurs in August in Colorado and Oregon, but may occur in late July to mid-September. Recently metamorphosed toadlets measure about 1.0-1.6 centimeters snout-vent length (SVL), but can be 1.6 to 2.0 centimeters.

Toadlets may overwinter along the borders of the pools where they developed or move to other nearby wetlands. Juveniles 2.0 to 3.5 centimeters SVL often are present in wetlands adjacent to breeding sites (Nussbaum et al. 1983, Hammerson 1999). Breeding adult males are 5.5 to 9.3 centimeters SVL, adult females 7.5 to 11.5 centimeters SVL. The minimum age of breeding males is four years, and six years for breeding females; captive animals have lived up to 35 years (Russell and Bauer 1993, Hammerson 1999).

The boreal toad was considered the most abundant amphibian of the western third of the state in previous decades (Rodgers and Jellison 1942, Brunson 1952, Maxell 2003), and is still encountered widely and frequently though by no means commonly, and is no longer ranked as the most abundant amphibian. Numerous surveys since the early 1990's indicate that this species has experienced regional population declines in the state. Boreal toads were documented to breed at only 2 to 5% of more than 2000 standing water bodies surveyed since 1997, and where breeding was documented, fewer than 10 breeding females contributed in a given year (Maxell 2000, Maxell et al. 2003). Thus, range-wide declines for this species in the western United States are also reflected in the Montana results. Because the reasons for declines in Montana remain obscure, it is difficult to suggest management techniques to reverse the trend. Nevertheless, the following should help reduce some immediate impacts. First, reduced access by livestock to known breeding sites within grazing allotments will prevent undue trampling mortality (Bartelt 1998). This can be accomplished by constructing partial or complete livestock exclosures (fencing) at breeding ponds and other sites. Second, use of fertilizers, herbicides, and pesticides within at least a 100 meters buffer zone of breeding sites should be avoided. Third, stocking predatory game fish at sites currently lacking them should be avoided, even though there is evidence that some species of trout do not prey on boreal toad tadpoles and eggs (Jones et al. 1999). And before efforts are enacted to remove undesirable fish by use of lethal chemicals, a survey for toads at the target water bodies should be conducted to prevent unnecessary mortality to any life stages. If toads are present, they can be removed by dipnet and held in captivity (under appropriate conditions) until the effects of the treatment dissipate, then returned to the site. Finally, known breeding sites should not be drained or altered, and water bodies where alteration is planned should first be surveyed for use by toads.