This species is only known from the western side of the Nguru Mountains, in the Morogoro Region of Tanzania (Loader et al. 2010). Most records are from the Maskati side of the Nguru South Forest Reserve (Loader et al. 2010). There is a single historical record from a site near Maskati Mission, which was found in forest, probably close to where later collections were made (Loader et al. 2010); it is unclear whether this site is also within the protected area . The recent description of numerous distinct species of Callulina, each with very restricted distributions on particular mountain ranges (Loader et al. 2010) suggests that it is unlikely to be much more widespread. This species has been recorded at elevations of 1,790 and 1,900 m asl. This frog appears to form part of an upper montane Nguru fauna characterized by endemic species that are not found at lower elevations (Loader et al. 2011). If it is genuinely confined to this elevational band the frog's extent of occurrence will be below 100 km2, but no more precise estimate is currently possible.
Habitat and Ecology
This frog has only been found in primary montane rainforest (Loader et al. 2010). The species appears to be mostly arboreal, with the majority of records from branches, and it has been observed from near ground level up to ca. 10 m above ground (Loader et al. 2010). Animals have, however, been found on bare rock, and there is a single historical record from within a rotting log (Loader et al. 2010). The frog's reproductive mode is unknown, however phylogenetic analysis has been used to predict that all brevicipitid frogs reproduce by terrestrial direct development (Müller et al. 2007).
In addition to a single historical record from 1982 this frog has been recorded in two surveys, one in 2004 and the other in 2008 (Loader et al. 2010). It was relatively common in both survey periods (S. Loader pers. comm. June 2011). There is otherwise no information on population densities in this species (Loader et al. 2010), and the population trend is unknown.
This species is likely to be dependent on primary forest. Cardamom and yams are cultivated at high elevations in the Nguru Mountains, and cardamom production is widespread within Nguru South Forest Reserve (Menegon et al. 2008). Although there is no evidence of major disturbances such as slash-and-burn agriculture, there is continuing pressure on the forest resulting from growth of the surrounding human population (S. Loader pers. comm. June 2011), and this is particularly intense around the borders of Nguru South Forest Reserve, with forests outside the reserve boundary having declined by over 60% between 1975 and 2003 (Doggart and Loserian 2007). The extent and impacts of forest decline in areas inhabited by this frog are difficult to evaluate (S. Loader pers. comm. June 2011), but its restricted distribution puts it at high risk from even small changes in forest cover.
The only recent records of this species are from within a proposed nature reserve, Mkingu Nature Reserve, which comprises the previously named Nguru South and Mkindo Forest Reserves (S. Loader pers. comm. April 2012). Currently, enforcement of this protection is limited (S. Loader pers. comm. June 2011). The protected status of this reserve is likely to be improved by designating it a Nature Reserve, and the site needs to be managed to enforce the new protection and limit the impacts of human activities on remaining primary forest (S. Loader pers. comm. June 2011). Further research is needed, to establish whether this frog occurs at lower elevations than is currently known, and to clarify its ecological requirements and exposure to threats.
Red List Status
Critically Endangered (CR)
Listed as Critically Endangered on the basis that it is known from a single location defined by ongoing pressure from human expansion into formerly forested land, it has an extent of occurrence below 100 km2, and there is a continuing decline in the quality and extent of its forest habitat that would require listing this species as Critically Endangered. If the species is found to have a wider elevational range than is currently recognized, it might have an extent of occurrence greater than 100 km2 and would therefore require reassessment.
Populations of Callulina from the Nguru Mountains were historically assigned to C. kreffti, as then understood a widespread East African montane species and the sole member of the genus. Menegon et al. (2008) recognized four distinct species among Nguru Mountains Callulina, two of which have since been formally described (Loader et al. 2010). One of these, C. kanga, appears to be restricted to the Kanga Forest Reserve (Menegon et al. 2008, Loader et al. 2010). The remaining three species are confined to blocks within the Nguru South Forest Reserve (Menegon et al. 2008, Loader et al. 2010). The name C. hanseni refers to "Callulina sp. 2" of these authors (Loader et al. 2010); the remaining populations are included within the Red List account for C. kreffti pending further research.
IUCN SSC Amphibian Specialist Group, 2012. Callulina hanseni. The IUCN Red List of Threatened Species 2012: e.T193425A2235726. http://dx.doi.org/10.2305/IUCN.UK.2012-1.RLTS.T193425A2235726.en .Downloaded on 23 January 2019