Red List of South African Species

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Least Concern (LC)
Assessors: Matthew Child John Power Ara Mondajem
Contributors: Claire Relton Nico Avenant Margaret Avery Rod Baxter Duncan MacFadyen Guy Palmer Peter Taylor Beryl Wilson
Reviewers: Matthew Child John Power Ara Mondajem

Rationale

The illegal harvesting of Acacia trees, especially Vachellia (previously Acacia) erioloba and Senegalia (previously Acacia) mellifera, across the range of this species is a major threat, as it reduces habitat quality through the destruction of nesting sites and food resources. Although widely distributed across the Acacia woodlands and shrublands of the northwestern parts of South Africa (including Northern Cape, North West and Limpopo provinces), this species was not recorded at all during a recent survey in North West Province, despite trapping effort of 380 trap nights and extensive spotlighting in the Molopo Bushveld vegetation type (R.J. Power unpubl. data) and the species was last recorded in Molopo in 2002. This suspected reduction in population over the last decade might qualify the species as Near Threatened A2c, but applying the regional criterion retains a Least Concern listing: the species is a good disperser and habitat is contiguous across both the Namibian and Botswana borders with presumed dispersal across countries. Additionally, it has a large potential area of occupancy (84,860 km2) based on remaining natural woodland habitats within its range.

Although the species is benefitted by legislation in place to protect Acacia trees (harvesting requires a permit), ongoing illegal harvesting could be causing a continuing decline in habitat quality. For example, the Camel Thorn Tree (V. erioloba) is a protected species in terms of the National Forests Act (No. 84 of 1998) but it is not always enforceable. More research needs to be done to quantify the impact of this threat on population size and trend and provide evidence for effective conservation interventions. This species should be reassessed as more data become available.

Regional population effects: There is likely dispersal from Namibia and Botswana, and there is contiguous habitat across the borders to South Africa. Black-tailed Tree Rats are considered good dispersers as long as there is tree cover.

Distribution

This largely southern African species has been recorded from western Angola in the north of its range, southwards through much of Namibia and Botswana to the northwestern parts of South Africa where it inhabits arid Acacia savannah. The precise delineation of this species’ range remains controversial, as it is often mistaken for T. paedulcus (Skinner & Chimimba 2005). More specifically, the eastern limits of its distribution are unknown, and it could extent further east (see Monadjem et al. 2015). Although Taylor et al. (1995) suggest that T. nigricauda and T. paedulcus have largely overlapping distributions extending throughout southern Africa (Skinner & Chimimba 2005), recent contrasting evidence suggests that it is more likely that much of their distributions do not overlap and T. paedulcus may be restricted to the eastern regions of southern Africa, and T. nigricauda to the western regions (see Monadjem et al. 2015). Further vetting of museum records is required to delimit the respective distributions of T. nigricauda and T. paedulcus. Similarly, the records on or south of the Gariep River must be vetted to ensure they do not refer to T. shortridgei (Monadjem et al. 2015). Currently, the degree of allopatry with T. shortridgei is unknown (Nel 2013).

A recent survey covering all vegetation types in the North West Province did not record this species, but did record T. paedulcus (Power 2013, 2014). It was last documented at Molopo Nature Reserve in 2000 (Eccard et al. 2006). Power (2014) speculated that an extensive fire in 1997, which burnt the whole northern half of the reserve, could have led to a local extinction, but this was disproved by evidence of a subpopulation present in 2002 (see Eccard et al. 2006; Meyer et al. 2008). Further field surveys are required from across its range to determine area of occupancy and other local extinctions.

Population trend

Trend

The Black-tailed Tree Rat is locally common in stands of suitable trees (those containing cavities for nesting), but patchily distributed throughout its range. This species was not recorded at all during a recent survey of the North West Province despite the trapping effort of 380 trap nights and extensive spotlighting in the Molopo Bushveld vegetation type (Power 2014). Across two reserves, the Molopo Nature Reserve and Khamab Kalahari Reserve, a total of 1,226 km and 72 hours was totalled over 52 surveys, and no individuals were encountered (R.J. Power unpubl. data). The dearth in not finding this species should be a cause for concern (Power 2014). Population declines can also occur after bush fires when smoke filters through the cavities as the number of inhabited trees in burnt areas (even where trees are just singed) are lower than unburnt areas (Nel 2013). Captive individuals were found to have a longevity of about 4 years (Jones 1982). In the Thornveld Savannah of South Africa, Meyer et al. (2008) recorded sex ratios of 1:1, and density estimates of 0.5–1 individual / ha.

Threats

The Black-tailed Tree Rat requires vegetation structure with intact woodlands for food and nesting sites. Resultantly, it is vulnerable to the harvesting of mature trees, especially V. erioloba and A. mellifera, for firewood or charcoal production (Eccard et al. 2006). This is a noted problem in the North West Province (DACE 2008), though not severe in extent, and commercial harvesting of Camel Thorn in the Northern Cape is thought to be largely restricted to dead trees (von Staden & Raimondo 2015).

Woodland clearing of Camel Thorn and Black Thorn (often with the use of pesticides) to enhance grassland establishment and increase grazing suitability for livestock may also cause a decline in habitat availability for this species. This occurs mainly in areas threatened by bush encroachment, as a result of poor land management (von Staden & Raimondo 2015). Incorrect fire regimes are also a root problem as it promotes overgrazing that removes the fuel load, which leads to bush encroachment (Driver et al. 2012).

Uses and trade

This species is not known to be utilised or traded in any form.

Conservation

This species is present within some protected areas across the assessment region, for example Kgalagadi Transfrontier Park (de Graaff 1978) and Tswalu Kalahari Reserve. No direct interventions are necessary at present. However, conservationists should protect woodland patches and ensure connectivity through protected area expansion and biodiversity stewardship schemes. Additionally, harvesting of large trees should be regulated to make the practice sustainable. The protected status of A. erioloba in South Africa should be maintained, due to its ecological importance, cultural value and the threats associated with uncontrolled and illegal harvesting for commercial firewood (Seymour & Milton 2003). North West Province has enlisted the Black-tailed Tree Rat as Specially Protected in their current Biodiversity Act owing to the concern in the status of the species there.

Recommendations for land managers and practitioners:
  • Subpopulations should be monitored to record any changes in abundance and distribution, and the monitoring of nest sites, and spotlight surveys, are suggested.
  • Land managers should be encouraged to conserve woodlands and old trees.
Research priorities:
  • Additional studies are needed into the taxonomic status of this species.
  • Analysis of museum records to more accurately delimit distribution.
Encouraged citizen actions:
  • Report sightings on virtual museum platforms (for example, iSpot and MammalMAP), especially outside protected areas. However, this species cannot be readily distinguished from T. paedulcus based on morphological characteristics.
  • Landowners can preserve Acacia trees, both living and dead.

References 

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,]
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