Ord’s kangaroo rat (Dipodomys ordii) COSEWIC assessment and status report: chapter 2
Ord’s Kangaroo Rat
Ord’s kangaroo rat (Dipodomys ordii Woodhouse 1853), a small, nocturnal rodent, is the only species of Dipodomys that occurs in Canada. It has large hind legs and feet, and mainly orange-brown dorsal pelage with distinctive white markings, including lateral stripes on the tail. The tufted tail accounts for more than half of total length (260 mm). Mean adult body mass is 69 g.
Ord’s kangaroo rat is widely distributed in the interior arid grasslands and deserts of western North America, from southern prairie Canada to central Mexico. In Canada, the species occurs in a small area of sand hills in southwestern Saskatchewan and southeastern Alberta as a disjunct population at the northernmost periphery of the species’ distribution.
Total extent of occurrence of kangaroo rats in Canada is 6030 km2, within which the area of occupancy is between 10 and 53 km2. Both extent of occurrence and area of occupancy have likely declined in recent decades. The Canadian population of Ord’s kangaroo rats functions as a metapopulation due to the highly dispersed and patchy nature of habitat and because patch turnover rates are high.
Ord’s kangaroo rat requires open, sparsely vegetated, sandy habitats to facilitate its hopping locomotion and extensive burrowing. Natural habitats consist of actively eroding sand dunes, sand flats, and sandy slopes of valleys in sand hill areas. Kangaroo rats also use sandy areas where the soil is disturbed by human land-uses (e.g., roads). These anthropogenic habitats may be low quality such that mortality exceeds recruitment.
Natural, sandy habitats are declining due to encroachment of vegetation. Climatic conditions contribute to dune stabilization, but land management such as fire suppression and altered grazing regimes presumably contribute to habitat loss. The extent of open sand in the Middle Sand Hills has declined by 40% per decade, on average, since 1949. Over the same period, the number of exposed dunes has declined at a rate of 7 per decade, representing a 53% loss from 1995 to 2005. If this continues, there will be no active dunes remaining in the Middle Sand Hills by 2014. Coincident to the loss of natural habitat, there has been a dramatic increase in anthropogenic habitat created by human land-use (e.g., roads) which is apparently less suitable and possibly a population ‘sink’. This rate of habitat loss and degradation appears representative of other areas within the species’ range in Canada.
Most kangaroo rat habitat in Canada occurs on provincial land that is leased for grazing cattle. Approximately 12% is contained in provincial and federal protected areas. Canadian Forces Base Suffield contains approximately 13% of the Canadian range of the species.
Most kangaroo rats in Canada survive less than one year, with annual survival frequently ≤10 %. The population typically reaches its lowest point during early spring. Reproduction is constrained to the snow-free period, generally from early spring to early autumn. Average litter size is 3 and adult females may rear up to 4 litters per year. Average age at first reproduction for females is approximately 47 d. Generation length is < 1 year.
Canadian Ord’s kangaroo rats exist in uncharacteristically cold and wet conditions for the genus. They are the only kangaroo rats known to use torpor to conserve energy during winter.
Kangaroo rats are territorial and defend burrows and underground food caches. Home range is generally ≤1 ha. Most dispersing individuals travel less than 500 m, though a maximum dispersal distance of 10 km has been recorded. Ord’s kangaroo rats are primarily granivorous but also eat other plant parts and insects.
Population Sizes and Trends
Estimates of population size of Ord’s kangaroo rats in Canada range between 545 and 1040 during seasonal low-point (early spring). The population exhibits extreme seasonal fluctuations due to summer reproductive output and low over-winter survival. In addition to within-year fluctuations, inter-annual fluctuations likely occur but are difficult to quantify. There are no data to allow an evaluation of inter-annual variation or population trends. However, changes in available habitat strongly suggest long-term population declines.
Limiting Factors and Threats
The primary factor governing long-term persistence of Ord’s kangaroo rats in Canada is likely loss and degradation of natural habitat. Additionally, the extreme seasonal fluctuation in population size puts the Canadian population at imminent risk of extinction. The trend towards increasing use of anthropogenic habitats appears to be a threat to Canadian kangaroo rats and is currently being directly evaluated. Other anthropogenic factors that may limit the population include industrial (specifically oil and gas) development and agricultural practices.
Special Significance of the Species
Kangaroo rats in Canada possess unique life history and physiological characteristics, and the species is a potentially useful focal species for conservation of prairie sand dunes, a rare and declining habitat that many species depend on.
Ord’s kangaroo rat was designated as special concern by COSEWIC in 1995 (then termed vulnerable). The global heritage status rank for the species is G5 (secure) and the provincial status rank is S2 (may be especially vulnerable to extirpation because of some factor of its biology) in Alberta and Saskatchewan. Kangaroo rats are considered endangered in Alberta under the Alberta Wildlife Act. In Saskatchewan, a portion of the species’ range has recently been protected in the Great Sand Hills under the Representative Areas Ecological Reserves Act. Slightly less than half of the species range in CFB Suffield is protected as a National Wildlife Area (NWA) under the Canada Wildlife Act.
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