Great Basin spadefoot (Spea intermontana) COSEWIC assessment and status report: chapter 2

Executive Summary

Great Basin Spadefoot
Spea intermontana

Species information

The Great Basin Spadefoot (Spea intermontana) is one of two species of spadefoots (family Scaphiopodidae, formerly Pelobatidae) that occur in Canada. Adults are about 40 – 65 mm long, and have a squat body form and relatively short legs for an anuran. The back is light grey, olive, or brown with lighter streaks and small raised dark blotches. Characteristic features include a black, keratinous ridge (“spade”) on the sole of each hind foot, used for burrowing, and a vertical, lens-shaped pupil.

Distribution

The Great Basin Spadefoot occupies the inter-montane region between the Rocky Mountains and Coastal Ranges from south-central British Columbia south to Arizona and Colorado. In Canada, the species is restricted to the arid and semi-arid zones of south-central British Columbia and occurs in the Okanagan Valley and in the Similkameen and Kettle-Granby river valleys in the south and in the Thompson and Nicola river valleys and the South Cariboo region in the north. Based on an estimation of about 235 discrete sites basedon records from 1985 to 2006, the extent of occurrence is about30,770 km². The area of occupancy is about 619 km², if calculated assuming a 1 km radius buffer around each discrete site, or 864 km², if calculated using a 2 km×2 km grid. From 1996 to 2006, the species continued to be found within all portions of its range. Most records are from the South Okanagan. Recent surveys in the North Okanagan, Nicola, and Kettle-Granby river valleys have established that the species is relatively widespread in these areas from where few previous records existed. In 2005 – 2006 it was found at 12 new sites in the South Cariboo, where it was previously known from two old records. Systematic surveys of historic sites have not been conducted, and local extinctions or range contractions cannot be determined.

Habitat

The Great Basin Spadefoot occupies grassland and open woodland habitats. It requires aquatic habitats for breeding and terrestrial habitats for foraging, hibernation, and aestivation. These habitats must be suitably connected to allow for seasonal movements. The species breeds in a variety of water bodies ranging from small pools to the margins of permanent water bodies and shallow areas of lakes but prefers temporary ponds that hold water for only part of each year. Spadefoots shelter underground from unfavourable conditions and require terrestrial habitat all year. Loose, deep, and friable (crumbly) soils that allow for burrowing and rodent burrows are thought to be important. Anecdotal observations and movements of other species of spadefoots suggest that individuals use terrestrial habitat within about 500 m of breeding sites.

Biology

Spadefoots respond rapidly to changing environmental conditions and breed explosively when temperatures are suitable and breeding sites are full of water. In British Columbia, adults begin to emerge from hibernation in early to mid-April and move quickly to breeding ponds where males begin to call. Females lay 300 – 800 black eggs in clusters of 20 – 40 in shallow water. Spadefoot tadpoles have among the shortest development times of all anurans, an adaptation that allows them to effectively exploit temporary pools. The entire development, from egg to toadlet, can be completed in as little as 5 weeks, but 6 – 8 weeks is more typical. In British Columbia, most metamorphosed toadlets appear in July and disperse from the breeding sites en masse. They attain reproductive maturity at 2 – 3 years and may live up to 10 years. Spadefoots have a variety of physiological adaptations for living in a dry environment, including the ability to survive relatively high water loss and absorb water directly from the soil while burrowed.

Population sizes and trends

There is no accurate information on population sizes or trends.The maximum population is probably at least 10,000 individuals, but much uncertainly is associated with this number and it could be much larger.However, it is almost certain that populations fluctuate greatly in size; the population at its lowest ebb may well fall below the 10,000 individual threshold. Most breeding choruses appear to be small; large choruses, consisting of hundreds of adult males, have been reported from a few sites.

Limiting factors and threats

The main threat to the Great Basin Spadefoot in British Columbia is from loss and degradation of habitat due to human activities. Dry grasslands, especially those in the South Okanagan, are under tremendous development pressures, from both intensive agriculture and urbanization, and habitat continues to be lost as the human population grows. Wetlands and temporary pools are naturally rare and continue to be lost and degraded. Other threats include habitat fragmentation, road mortality, pesticides, sport fish and bullfrog introductions, and degradation of breeding sites and their margins by livestock.

Special significance of the species

The Great Basin Spadefoot is part of a suite of grassland and open woodland species that is restricted to the southern interior of British Columbia. Although not used for food or medicinal purposes, spadefoots are considered beneficial as they provide food for other animals, such as turtles.

Existing protection

Most of the habitat suitable for the Great Basin Spadefoot is unprotected. Close to 70% of the species’ range in British Columbia is either privately owned or within Aboriginal lands. Some populations occur within areas protected from development both in the south ( Haynes’ Lease Ecological Reserve, South Okanagan Wildlife Management Area, White Lake Grasslands Protected Area, South Okanagan Grasslands Protected Area) and in the north (Lac du Bois Grasslands Protected Area). The species is designated as an “Identified Wildlife” species under the BC Forest and Range Practices Act and is subject to mandatory implementation of management guidelines on provincial crown lands. It is listed as “Threatened” under Schedule 1 of SARA.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.  On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species. 

Definitions

Species
Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)
A species that no longer exists.

Extirpated (XT)
A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A species facing imminent extirpation or extinction.

Threatened (T)
A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)*
A species that has been evaluated and found to be not at risk.

Data Deficient (DD)***
A species for which there is insufficient scientific information to support status designation.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Page details

Date modified: