Rationale
This is a rare species endemic to South Africa, Swaziland and Zimbabwe, existing in moist grassland habitats in the Savannah and Grassland biomes. Although it has a wide inferred extent of occurrence (284,735 km2), it appears to be patchily distributed. We use wetlands as a proxy for suitable habitat and calculate the amount of natural habitat remaining within buffer strips around wetlands as the inferred area of occupancy (AOO), which yields a range of 1,790â2,089 km2 (32 m buffer strip). We suspect that these habitat patches are severely fragmented as shrews have a poor dispersal ability, and continuing rates of urban and rural expansion (highest rates are 15% and 9%, respectively, in Limpopo Province) may have increased overgrazing and water abstraction, which may reduce the suitability of patches and the corridors between them. Similarly, we infer a continuing population decline based on high rates of habitat loss in all provinces, especially KwaZulu-Natal and North West (1.2% per year from 1994â2011 and 0.5% per annum from 2006â2010, respectively). Thus we list this species, under a precautionary purview, as Vulnerable B2ab(ii,iii,iv) because, although the AOO estimate varies widely, not all suitable habitat will be occupied (for example, not a single individual was sampled during a recent survey in North West Province). We recommend more field studies be undertaken to understand the distribution and density of the species. If new data indicate a wider AOO and confirm its broad habitat tolerance, a reassessment will be necessary and it may be downlisted to Near Threatened or Least Concern.
Key interventions include protected area expansion of moist grassland and riverine woodland habitats, as well as providing incentives for landowners to sustain natural vegetation around wetlands and keep livestock or wildlife at ecological carrying capacity.
Regional population effects: This species is suspected to have a low dispersal capacity and exists in fragmented habitat. Thus, we assume no rescue effects are possible.
Distribution
This is a rare species, recorded only from disparate localities in Zimbabwe, Mantenga Falls in the middleveld region of Swaziland (Monadjem 1998), Limpopo (Motlateng and Blouberg, and more recently in the Soutpansberg Mountains; P. Taylor unpubl. data), North West (Makwassie), Gauteng (Krugersdorp, Roodeplaat Dam and Heuningklip), KwaZulu-Natal (Kosi Lake, Lake Sibaya, Gaintâs Castle, Royal Natal and Chase Valley Heights) and Mpumalanga (Loskop Dam) (Skinner & Chimimba 2005). The species may be considered near-endemic or endemic if molecular work reveals a species complex existing across regions and biomes. Additionally, the Highveld grassland population may turn out to be taxonomically distinct from the subtropical grassland population (P. Taylor unpubl. data).
Although the type locality of the species is the town of Maquassie, North West Province (discovered in 1928 in a house), it has been infrequently recorded in the province and there have been no post-1999 records despite a recent survey that sampled the Klipspruit region around Maquassie that may form part of a dispersal corridor for the species (Power 2014). Countrywide, post-1999 records for the species pertain only to the Soutpansberg Mountains (Taylor et al. 2015) and northern KwaZulu-Natal (P. Taylor unpubl. data). Similarly, both Friedmann and Daly (2004) and Baxter (2008) indicate a possible occurrence for the species in southern Free State Province on the Orange River, but this revision does not have a record for this area and its presence has not been detected in the Free State in recent surveys (N. Avenant pers. comm. 2016).
Based on the scattered records available, we infer the extent of occurrence to be 284,735 km2. However, we suspect the species to be patchily distributed within this wide area. As the species depends on moist habitats, we use wetlands as a proxy for suitable habitat and calculate the amount of natural habitat remaining within buffer strips around wetlands as the inferred area of occupancy (AOO), which yields a range of 40,496â47,246 km2 (using a 500 m buffer strip) to 1,790â2,089 km2 (using a 32 m buffer strip). Although this is still a huge area, we suspect the lower estimates are more plausible as not all suitable patches will be occupied due to the natural rarity of the species, its poor dispersal capacity and ongoing habitat degradation of patches and corridors between them.
Population trend
Trend
This species is small, relatively rare and seldom caught in traps during sampling. Research from Luvhondo Nature Reserve in the Soutpansberg Mountains, indicates a low-density population, where only two individuals were captured over a year-long period (2010â2011) in half-hectare plots (Taylor et al. 2015). This equates to a trap success of 0.005 captures / trap night and an inferred density of around 1 individual / 0.01 km2 (P. Taylor unpubl. data). If we extrapolate this density across the lowest estimate of AOO, it yields a population size of at least 179,000 individuals.
Its rarity is also corroborated through recent field studies in Mkhuze and Phinda Game Reserves, KwaZulu-Natal where, despite being within the range of the species, it was not sampled whilst other Crocidura species were (Delcros et al. 2014; Rautenbach et al. 2014). Thus, this may be a naturally rare species that is difficult to identify and has been overlooked. Although more information and sampling is needed, this species is likely to persist in areas with moist conditions.
Threats
The main threats to shrews are the loss or degradation of moist, productive areas such as wetlands and rank grasslands within suitable habitat. The two main drivers behind this are abstraction of surface water and draining of wetlands through industrial and residential expansion, and overgrazing of moist grasslands, which leads to the loss of ground cover and decreases small mammal diversity and abundance (Bowland & Perrin 1989, 1993). Suppression of natural ecosystem processes, such as fire, can also lead to habitat degradation through bush encroachment or loss of plant diversity through alien invasive infestation, and is suspected to be increasing with human settlement expansion. There are also clear overlaps and synergistic effects between these threats. We infer a continuing population decline based on loss of natural habitat.
Wetlands are the countryâs most threatened ecosystem, with 65% of wetland ecosystem types threatened (48% of all wetland types Critically Endangered, 12% Endangered and 5% Vulnerable) because they are highly productive and hence become transformed for agriculture (Driver et al. 2012). Overall, 45% of our remaining wetland areas exist in a heavily modified condition, due primarily to onsite modification from crop cultivation, coal mining, urban development, dam construction, and overgrazing (and thus erosion) and off-site modifications from disruptions to flow regime and deterioration of water quality (Driver et al. 2012).
Uses and trade
There is no known subsistence or commercial use of this species.
Conservation
This species occurs in Maloti-Drakensberg Transfrontier Park and presumably several other protected areas. The main intervention for this species is the protection and restoration of wetlands and grasslands. Biodiversity stewardship schemes should be promoted if landowners possess wetlands or grasslands close to core protected areas or remaining habitat patches, and the effects on small mammal subpopulations should be monitored. Protecting such habitats may create dispersal corridors between grassland patches that will enable adaptation to climate change. At the local scale, landowners and managers should be sensitised, encouraged and incentivised to conserve the habitats on which shrews and other small mammals depend. Retaining ground cover is the most important management tool to increase small mammal diversity and abundance. This can be achieved through lowering grazing pressure (Bowland & Perrin 1989), or by maintaining a buffer strip of natural vegetation around wetlands (Driver et al. 2012). Small mammal diversity and abundance is also higher in more complex or heterogeneous landscapes, where periodic burning is an important tool to achieve this (Bowland & Perrin 1993). Removing alien vegetation from watersheds, watercourses and wetlands is also an important intervention to improve flow and water quality, and thus habitat quality, for shrews. Education and awareness campaigns should be employed to teach landowners and local communities about the importance of conserving wetlands and moist grasslands.
Recommendations for land managers and practitioners:
- Landowners and communities should be incentivised to stock livestock or wildlife at ecological carrying capacity and to maintain a buffer of natural vegetation around wetlands.
- Enforce regulations on developments that potentially impact on the habitat integrity of grasslands and wetlands.
Research priorities:
- Additional field surveys are needed to clarify and confirm the distribution of this species.
- Further molecular research may be needed to disentangle a possible species complex.
Encouraged citizen actions:
- Citizens are requested to submit any shrews killed by cats or drowned in pools to a museum or a provincial conservation authority for identification, thereby enhancing our knowledge of shrew distribution (carcasses can be placed in a ziplock bag and frozen with the locality recorded).
