Great Basin Spadefoot Toad
The habitat of this dryland-adapted amphibian is under tremendous development pressure.
Ministry of Environment, Lands and Parks grasslands, cattle may congregate around variety of ducks and shorebirds, while water sources, including the small ponds Killdeer and Common Ravens have been used by spadefoots for breeding. Deep seen eating dying larvae in a drying pond. cattle hoofprints can create a multitude of Painted Turtles may be important preda- Why are Great Basin tiny pools as a pond dries up instead of a tors on larvae as well. Spadefoot Toads at risk? single, larger pool. This can increase The nocturnal habits of the Great he Great Basin Spadefoot Toad is evaporation and decrease tadpole sur- Basin Spadefoot Toad and its tendency restricted in Canada to dry grassland vival. On the positive side, irrigation to remain underground for much of the valleys in south-central British Colum- projects can benefit the species by provid- year make it a difficult species to study, T bia, with the Okanagan Valley having ing dependable breeding ponds in other- and we have much to learn about its the largest population concentration. The wise dry areas. These projects, however, biology in British Columbia. low-elevation dry grasslands of the Okana- may seriously impact the amount and gan are one of Canada’s most endangered quality of foraging habitat available to What is their status? ecosystems with less than nine percent of spadefoots by converting natural habitat padefoot toads are relatively widely dis- this habitat remaining undisturbed. The to agricultural croplands. tributed through the dry grasslands of region faces tremendous development The quality of habitat in remaining the Southern Interior of British pressures, both from intensive agriculture grasslands is a more difficult question S Columbia, but these grasslands make and urbanization. to address. Since little is known about up only six percent of the province. The Great Basin Spadefoot the foraging needs of Within these grasslands, spadefoots are Toad needs three quite separate Great Basin Spadefoot restricted to areas with access to breeding habitats: breeding ponds, forag- Spadefoot Toads, the effects of ponds. During recent censuses, over half ing areas, and hibernating sites. Toads may grazing or other dis- the calling males were found at only three Dispersal routes between these turbances are difficult sites. Two of these three significant breed- habitats are also required. Per- stay below to assess. As well, ing areas are protected. haps the most critical variable for ground for almost nothing is Only three population surveys have an amphibian living in an arid known about the been undertaken in British Columbia. environment is the availability of up to eight hibernating sites used The current population is probably at water for breeding. Great Basin months by this species. Con- least 10 000. The range of the Great Spadefoot Toads typically breed cern has been raised Basin Spadefoot Toad in British Colum- in small ponds that may dry up each year. over the effect of soil bia extends from the provincial border in July or August. These ponds compaction by cattle, in the south, up through the Thompson must last at least six weeks for larval which may reduce the water content of and Okanagan valleys and north to 70 development to take place, usually the soil and also make it difficult for Mile House in the Cariboo, to Barriere finished by the end of June. In the last spadefoots to burrow below the surface. along the North Thompson River and to 20 years the water table has dropped Fragmentation of foraging habitat has Big Bar Creek along the Fraser River. significantly at many sites in the Cana- almost certainly disrupted traditional They occur west to Princeton in the dian range of the Great Basin Spadefoot spadefoot toad dispersal routes between Similkameen Valley. Until recently they Toad. While this drop is partly due to breeding, foraging and hibernating sites. were unrecorded east of the Okanagan reduced precipitation over that time The increase in the number of roads, and Valley, but in 1996, two adults were seen period, accelerating human develop- more importantly, the amount of traffic, just east of Grand Forks. It is presumed ment in these areas and the consequent may have a significant impact on spade- that the British Columbia population increase in the number of wells that foot populations by increasing the number has decreased due to loss of prime have been dug is undoubtedly also of spadefoots killed on roads. breeding, foraging and hibernating lowering the water table. Although adult toads have noxious skin habitats, particularly in the Okanagan. Water quality and temperature are secretions to deter predation, they are As a dryland amphibian at the north- also important to breeding success, and eaten by snakes and larger predators such ern edge of its range, the Great Basin water quality is often highly variable in as Great Blue Herons and Coyotes. An Spadefoot requires a delicate balance of the small ponds used by spadefoots. The adult Tiger Salamander was observed eat- climatic variables. A series of hot, dry high pH of many small ponds in their ing an adult Great Basin Spadefoot Toad in summers may cause a population decline range may be a limiting factor. In dry captivity. Tadpoles are likely eaten by a through the reduction of low-elevation breeding sites, but may open up new habi- What do they look like? son. Spadefoot tadpoles are large and dark tats at higher elevations. A series of cool, he Great Basin Spadefoot Toad (Spea grey, with close-set, raised eyes. wet summers might have a negative effect intermontana) is a small toad with a through the reforestation of grassland body length of 4 to 6.5 centimetres What makes them unique? habitat, reducing the extent and quality of T from snout to vent. It is grey-green lthough amphibians are usually asso- foraging habitat and likely increasing with numerous dark brown or reddish ciated with ponds and marshes, the competition with other frogs and toads. tubercles and spots, and a greyish-white Great Basin Spadefoot Toad is a dry- The Great Basin Spadefoot Toad is belly. Its limbs are relatively short. Its blunt A land amphibian. All spadefoot toads protected under the British Columbia snout is somewhat uptilted and a small occupy open, semiarid to arid habitats not Wildlife Act, but this legislation only lump or “boss”can be felt between the eyes. normally associated with their water-lov- covers the capture or killing of individ- Like all members of the spadefoot family, ing relatives. They cope with this lack of uals, not matters affecting their adult Great water by burrowing underground and habitat. It is on the provincial Blue Basin Spade- remaining dormant through dry or cold List of species considered vulnera- Great Basin foots have a periods. Great Basin Spadefoot Toads may ble. The Committee on the Status Spadefoot characteristic stay below ground for up to eight months of Endangered Wildlife in Canada black, kerati- each year. They emerge when a combina- () has designated the Toads breed in nous “spade” tion of warm weather and wet soil from species as Vulnerable. ponds fed by on the sole of rainfall or snowmelt provides the proper The Great Basin Spadefoot each hind foot conditions for survival above ground. Toad is not considered threatened snowmelt that helps Spadefoots also have a variety of adapta- or endangered in the United and rainwater. them dig into tions for living in a dry environment, States, but the species has lost a loose soil. including the ability to recover from considerable portion of its habitat Great Basin extreme desiccation. They can lose up to 48 there to intensive agricultural develop- Spadefoots also have distinctive vertical percent of their body weight in water and ments. It is found in dry grasslands “cat’s-eye” pupils. Males – which are some- still survive. north of the Colorado River, east of the what smaller than females –have dark The Great Basin Spadefoot Toad Sierra Nevada and Cascade ranges and throats and develop black pads on their breeds in ponds fed by snowmelt and west of the Rocky Mountain divide. inner three fingers during the breeding sea- rainwater. Since many of these ponds dry up in early summer, breeding success is up to 200 metres away. When mating, the Present range of the Great affected by fluctuations in water table smaller male grasps the female around her Basin Spadefoot Toad levels, precipitation and air temperature waist with his forearms. As the female lays in Canada and the United States in spring and summer. While the biology her eggs, the male fertilizes them external- of several desert-dwelling spadefoot toad ly. The 300 to 800 black eggs are laid in species has been intensively studied, rela- clusters of 20 to 40 attached to sticks, peb- tively little is known about the more bles or aquatic vegetation. northern Great Basin Spadefoot Toad. The length of the breeding season is Because it occupies somewhat different measured by the presence of calling habitats, it may have significantly differ- males. At any given site it can vary from ent life strategies than the desert species. one month to less than a week. Sites The size of breeding populations occupied earlier in the season have call- probably varies substantially from year ing toads longer than those occupied to year depending on water table later in the summer. levels, temperature and rainfall. If Spadefoot The breeding season a pond begins to dry up during in the northern parts larval development, older tad- Toads may of the species’ range poles can accelerate metamor- stay below lasts from April to phosis to some extent, but are June. It may be limit- thus smaller when they leave the ground for ed by the sensitivity pond, and smaller adult spade- up to eight of eggs to high water foots lose water more quickly temperatures. While than larger ones. months this has not been Great Basin Spadefoot Toads each year. studied in the Great they leave the water. In British Colum- go into hibernation in October Basin Spadefoot Toad, bia, most tadpoles are seen in May and in British Columbia. Some newly laid eggs of most metamorphosed toadlets appear in spadefoot species can theoretically closely related spadefoot species perish at July. Fungal infections may have a remain dormant for two or more years temperatures of 37˚C. significant impact on the survival of waiting for suitable foraging and Eggs hatch in two to three days dur- eggs, but detailed information on egg breeding conditions, but it is ing warm weather, but can take up to and larval survival is completely lacking. unknown whether the Great Basin seven days or longer in cooler weather. Dispersal from natal ponds can occur Spadefoot Toad has or even needs this Hatchlings are 5 to 7 millimetres long. en masse. Hundreds of small, newly ability. The maximum longevity of the They grow quickly, metamorphosing metamorphosed spadefoot toads are Great Basin Spadefoot Toad is into toadlets when 30 to 70 mm long, six often seen crossing roads. There are no unknown, but other spadefoot species to eight weeks after hatching. Young data on dispersal distances, nor on dis- can live 10 years or more. toads average 20.5 mm long (snout-to- tances between foraging, breeding and vent length) at metamorphosis and hibernating areas. How do they reproduce? often still have a substantial tail when padefoot toads become sexually mature What do they eat? by their second or third year, when Present range of the Great Basin Spadefoot padefoot tadpole larvae are voracious Toad in British Columbia males measure about 4 cm in length and scavengers on algae, aquatic plants, S females about 4.5 cm. Adults begin to dead fish and even their own faeces. emerge from hibernation in early to mid S Other species of spadefoots are April and move quickly to breeding ponds. known to have carnivorous tadpole There, the males begin to chant, distending morphs (genetic variants) that specialize their vocal sacs to produce their monoto- in eating brine shrimp, and sometimes nous, grating “gwaa, gwaa” call, which says become quite cannibalistic. These morphs “come hither” to the females. As the males can grow and metamorphose more call in response to each other, they create a Kamloops quickly than the scavenging tadpoles, so chorus of voices at different pitches, audible are more likely to survive where small ponds dry up quickly in early sum- The concentration of half the mer. It is not known whether Great population of breeding males in Basin Spadefoot tadpoles ever two areas – the Osoyoos Oxbows exhibit this type of behaviour. at the north end of Osoyoos Lake, Adult spadefoot toads eat a and the Osoyoos sewage lagoon – variety of invertebrates, includ- makes protecting these local ing earthworms, ants, beetles, areas of critical importance. The crickets, grasshoppers and flies. Haynes Lease Ecological Reserve They forage nocturnally, espe- provides 100 hectares of secure cially on rainy nights or nights habitat for the large population with high humidity. Little is breeding and foraging at the known about their foraging habi- north end of Osoyoos Lake. tat requirements. Some other . Leah Ramsay photo The adjacent South Okanagan spadefoot species can obtain Wildlife Management Area pro- enough food energy to survive a year of In the Thompson-Nicola area, spade- vides additional habitat for that dormancy in as few as seven feedings. foots clustered around seepage areas population, but at a lower level of pro- where fresh water was entering small tection. Perhaps the most endangered Where do they live? ponds. The pH was around 8.5 at the population of spadefoots is the 1000 n the United States, Great Basin Spade- seepage sites and about 10 elsewhere in or so breeding pairs at the Osoyoos foot Toads are found in a variety of dry the pond where the toads were absent. sewage lagoon which represent almost grassland and open woodland habitats, Competition with other frogs and one-quarter of the known Great Basin I including sagebrush flats, semidesert toads, particularly the Pacific Treefrog, Spadefoot Toads in Canada. shrublands, juniper woodlands and, in the could exclude spadefoots from certain As of 1994, less than one percent southern part of their range, open spruce-fir breeding sites. Researchers have noted of British Columbia’s grasslands was forests. In British Columbia they occur over adjacent ponds occupied exclusive- protected, although a wide range of elevations, but most are ly by either treefrogs or spadefoots. Survival of this figure has risen found below 600 metres in bunchgrass habi- This aspect of spadefoot ecology somewhat with new tats. Smaller concentrations occur in open clearly needs further study. Spade- these toads protected areas be- ponderosa pine and Douglas-fir forests up foots may also be excluded from requires ing set aside by the to 1200 m. A few tadpoles have been found ponds with large numbers of provincial govern- in small lakes as high as 1800 m. Painted Turtles. protection ment in the Churn Because spadefoots burrow under- of breeding Creek and Lac du ground to minimize water loss, they need What can we do? Bois areas. The latter either loose, uncompacted soil for easy he Great Basin Spadefoot Toad ponds, area includes the burrowing, or access to rodent burrows is one of a number of wildlife foraging third-largest known for daytime retreats. species at risk that live in the spadefoot breeding areas and Detailed surveys have been carried T grasslands and open woodlands site. The Nature Trust out in the south Okanagan and the of the Southern Interior of British hibernating of British Columbia Thompson and Nicola valleys. Out of Columbia.Animals such as the Pigmy has acquired sever- approximately 4200 singing males count- Short-horned Lizard, Night Snake, sites. al properties with ed during censuses between 1993 and Gray Flycatcher and Pallid Bat, as well spadefoot toad habi- 1996, 60 percent of the population was as a host of rare insect and plant species, are tat, the most significant being the White found at 56 sites in the South Okanagan, found nowhere else in Canada.As with other Lake Ranch west of Okanagan Falls. 35 percent at 24 sites in the Thompson species at risk, the Great Basin Spadefoot Further sites in the south Okanagan- Valley, and 5 percent at 31 sites in the Toad is limited by the availability and quali- Similkameen area may be set aside as well, Nicola Valley. No surveys have been done ty of its required habitat. Survival of these as part of the ongoing Okanagan-Shuswap in the north Okanagan Valley, but there toads requires protection of breeding ponds, Land and Resource Management Plan. are specimen and sight records from that foraging areas and hibernating sites. The Water bodies of all sizes adjacent area and suitable habitat is abundant, toad must also be able to travel along disper- to grasslands should be maintained especially around Vernon. sal routes between these habitats. wherever possible throughout the species’ “” . . . Steve Cannings photo Steve Cannings photo Steve Cannings photo
monitoring surveys should be set up to hibernation and foraging areas around assess population levels. The surveys could the large breeding ponds in the Lac du be done by trained volunteers, but must be Bois region, Osoyoos sewage lagoons and organized by wildlife conservation agen- Osoyoos Oxbows should also be docu- cies. This could be in the form of a broad- mented. Until this research is undertak- er survey for all amphibian species, or en, all native grasslands surrounding could focus on spadefoot toads. These sur- these sites should be managed for veys should cover known concentrations, wildlife conservation, maintaining a but also systematically census the North mosaic of grassland habitats at different Okanagan, Similkameen, Grand Forks and stages in development. . Richard Cannings photo Cariboo-Chilcotin areas. Information on Your support for further Great Basin distribution of this species is maintained Spadefoot Toad research and for the pro- range in Canada. This includes tempo- by the BC Conservation Data Centre. tection of breeding sites, is important to rary ponds that may only be filled with Information about soil characteristics the long-term survival of British Colum- water for a short time or only in wet and plant life of movement corridors and bia’s only desert-adapted amphibian. years. Development on privately owned land next to major breeding sites could be , : designed to preserve a permanent source Wildlife Branch of foraging and hibernating sites and Ministry of Environment, Lands and Parks movement corridors. Private land-own- PO Box 9374, Stn. Prov. Govt. ers should be encouraged to maintain Victoria, British Columbia V8W 9M4 and enhance habitat by fencing ponds to www.elp.gov.bc.ca/wld minimize damage by livestock. Amphib- ian culverts could be installed as part of new or existing roadways that cut through critical movement corridors near major breeding sites. Fish introduc- tions should not be considered in ponds known to support breeding populations of spadefoot toads. More basic biological information is critically needed for this species. Almost and by Forest Renewal British Columbia . nothing is known about the habitat vari- --- , ables that might explain the distribution of . toads in breeding ponds, including water chemistry, temperature, aquatic vegeta- tion, competition with other species and food availability. A system of periodic Printed in British Columbia on recycled paper with vegetable inks Q.P.4500015472