Ord’s kangaroo rat (Dipodomys ordii) COSEWIC assessment and status report: chapter 10
Limiting Factors and Threats
The primary factor in the long-term persistence of Ord’s kangaroo rats in Canada is loss and degradation of natural habitat. Additionally, the combination of a relatively small population that undergoes substantial seasonal fluctuations puts Canadian Ord’s kangaroo rats at imminent risk of extinction. While population fluctuation has a natural component, there are anthropogenic factors that likely contribute to the amplitude of fluctuation.
Historical and ongoing declines of natural, sandy habitats in the Great Sand Hills and Middle Sand Hills are well documented (Wolfe et al. 1995, Vance and Wolfe 1996, Muhs and Wolfe 1999, Bender et al. 2005, Hugenholtz and Wolfe 2005). The prediction that 100% of dune patches in the Middle Sand Hills will disappear by 2014 if current trends continue (Bender et al. 2005) is alarming given that these types of habitat appear to be prerequisite for the species’ persistence in Canada. Stabilization of open sand in the sand hills is generally driven by more humid conditions. However, land management, such as long-term suppression of fire, removal of large mammals that ranged widely and had heterogeneous effects on vegetation cover on the landscape (bison, Bison bison, and elk, Cervus elaphus), and practices which discourage erosion in sand hill areas, have obscured the natural trend. All of these factors have presumably contributed to stabilization of open sand. Noteworthy is the fact that the use of flax bales to discourage erosion in the Middle Sand Hills by CFB Suffield was discontinued in 1992 (Davies pers. comm. 2005), and in 1997 and 1998 elk were re-introduced in CFB Suffield in an effort to reestablish a large grazer. These steps may aid in slowing or reversing losses of natural sandy habitats in that area. In addition, the Alberta Ord’s kangaroo rat Recovery Team (2005) has proposed that experimental habitat management and development of a beneficial management plan (BMP) for maintaining active sand dune habitats is a high priority for 2005 to 2009. Fire and grazing management policies, shrub removal (Price et al. 1994), and physical reactivation of sand hills are possible.
Coincident to losses of natural habitat, human land-uses have rapidly overlaid a dense array of highly connected features on the landscape (e.g., access roads). Kangaroo rats’ tendency to opportunistically colonize open sandy areas created by human disturbance may contribute to the severity of population fluctuations. Kangaroo rats that inhabit roads and fireguards: (i) have low survival rates and are prone to local (patch) extinctions (Gummer 1997a, Gummer and Robertson 2003b, Gummer unpubl. data); (ii) experience higher rates of botfly parasitism than kangaroo rats in more natural habitats (Bender et al. 2005, Gummer unpubl. data); (iii) have a significantly lower body mass index than kangaroo rats in more natural habitats (Bender et al. 2005). The long-term trend towards increasing anthropogenic habitats is a threat to Canadian Ord’s kangaroo rats despite their apparent use of these areas. This hypothesis is currently being evaluated more rigorously (Bender et al. unpubl. data).
A large proportion of anthropogenic disturbances in the sand hills are associated with oil and gas development, so habitat degradation likely represents the principal effect of oil and gas development on kangaroo rats. There may be additional, direct effects of industrial activities such as seismic surveys, drilling wells, artificial lighting, auditory disturbances, and reclamation practices. Effects of pipeline construction on resident kangaroo rats have been studied intensively and several mitigation measures appear to effectively minimize direct mortalities of kangaroo rats (Gummer and Robertson 2003c).
Agricultural practices primarily affect kangaroo rats in three ways: (i) seasonal grazing of livestock in intact prairie that has not been cultivated; (ii) diligent management to discourage soil erosion, suppress fire, and generally increase vegetation cover; and (iii) conversion of natural, sandy habitats to anthropogenic habitats by cultivation. Livestock grazing is generally compatible with kangaroo rats and could potentially be managed to increase open, sandy habitats in some areas (Reynolds 1958). Although some kangaroo rats may be trampled by livestock or crushed in their underground burrows, this is likely outweighed by the benefits of reduced vegetation cover and increased amounts of open, sandy habitats. Conventional range management to reduce erosion and maintain or enhance vegetation cover may require innovative programs and incentives to favour sand dune conservation. Conversion of sandy habitats to cultivated lands is currently uncommon, but previously converted lands may contribute to the severity of population fluctuations by serving as population sinks.
Rural and industrial developments presumably limit kangaroo rat populations in some areas. The footprint and artificial lighting of buildings and other permanent installations may inhibit kangaroo rats. Although the majority of kangaroo rat range is probably not subject to imminent development, large gas refineries and other industrial installations (e.g., gas compressor stations) continue to expand and increase in numbers. Additional expansion and additions of similar installations in other areas of kangaroo rat range may cause declines in local populations of kangaroo rats through habitat loss and interference with nighttime foraging behaviour and predator avoidance.
Approximately 13% of the Canadian range of Ord’s kangaroo rat occurs in CFB Suffield, which is used intensively for military training. Military activities do not occur within the portion of the military lands designated as a National Wildlife Area and thus should not impact the population there. It is likely that the relatively small number of kangaroo rats that may be killed by vehicles or crushed in their underground burrows is outweighed by the fact that military exercises also generate frequent grass fires and create localized disturbance of the soil surface that may create habitat for kangaroo rats.
Botfly parasitism appears to be a limiting factor for the Canadian population of Ord’s kangaroo rats because it compromises reproduction and over-winter survival of kangaroo rats (Gummer unpubl. data). Kangaroo rats are much more susceptible to botfly parasitism in anthropogenic habitats (Bender et al. 2005).
Like any small population that fluctuates in numbers, the Canadian population of Ord’s kangaroo rats is highly susceptible to extinction from stochastic events including extreme weather events, unforeseen human disturbances, disease outbreaks, demographic stochasticity, genetic bottlenecks or in-breeding effects, and difficulty finding mates when populations are low. Winter severity, appears to be a critical, limiting factor for kangaroo rat survival (Gummer 1997a, Gummer and Robertson 2003c, Gummer 2005).
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