As stated in the taxonomic note, pending taxonomic resolution of this complex, we here treat Callulina kreffti are referring to all populations of Callulina except those in the West Usambara mountains (C. dawida); it is expected that the name C. kreffti will eventually apply only to animals from the East Usambara mountains, northeastern Tanzania (with populations from elsewhere likely to be described as new species) (Loader et al. 2010a, 2010b). The species is known from the Taita Hills and Shimba Hills in Kenya, and from the Pare, East Usambara, Nguu, Nguru, Ukaguru, Uluguru, Rubeho, Udzungwa and Mahenge Mountains in Tanzania (Loader et al. 2010b, 2014). Krefft's Warty Frog occurs from foothills (down at least to 300 m asl) up to 2,200 m asl. The estimated extent of occurrence (EOO) is 101,070 km²; the species' true EOO, if it is genuinely restricted to the East Usambaras, will be in the region of 520 km².
Habitat and Ecology
This frog lives on the forest floor, hiding under rotting logs or stones. It can also climb to at least 2 m in the vegetation, and has been found in the leaf axils of both wild and cultivated banana plants. In most places it is somewhat tolerant of habitat degradation, but generally needs to be close to mature forest, though it has been found far from forest in degraded habitats in the Ukaguru Mountains (this sub-population may prove to be a different species). 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).
The species is secretive, but during the rains it is not uncommon. As its forest habitat is under pressure throughout its range, this frog's population is presumed to be declining: the available habitat within the East Usambaras is heavily fragmented by human activities, and the distribution of remaining forest is patchy; there is limited dispersal between the habitat fragments in this area.
This frog is adversely affected by ongoing forest loss caused by small-scale and agro-industry farming, and wood extraction, although rates of forest loss in much of the Eastern Arc have declined in recent years (Hall et al. 2009). However, its habitat in the East Usambaras has recently come under serious threat as a result of the activities of illegal gold miners, and several reports suggest that forest loss in this area is dramatic and ongoing (S. Loader pers. comm. June 2011).
It is known with certainty from the Amani Forest Reserve, and may occur in Shimba Hills National Park. A subpopulation currently included within this species has been found in the Udzungwa National Park. These reserves need to be managed to limit the encroachment of agricultural and mining activities into remaining forest. Research is needed to clarify the taxonomy of undescribed members of this species complex and to clarify the true distributional extent and ecological requirements of Krefft's Warty Frog.
Red List Status
Least Concern (LC)
Listed as Least Concern due to its relatively wide distribution, tolerance of a broad range of habitats, and its presumed large population.
Prior to its description Callulina dawida was considered to belong to Callulina kreffti (Loader et al. 2009). Callulina kreffti as now understood is a restricted-range species that may be endemic to the East Usambara Mountains (Loader et al. 2010, 2014). However, for the purposes of the 2014 assessment, we count all Callulina populations, other than C. dawida, as Callulina kreffti pending taxonomic resolution of this complex (J. Luedtke and S. Stuart pers. comm. December 2014).
IUCN SSC Amphibian Specialist Group 2015. Callulina kreffti. The IUCN Red List of Threatened Species 2015: e.T62181621A3062808. http://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T62181621A3062808.en .Downloaded on 19 January 2019