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The Shimba Hills are a dissected plateau that ascends steeply from the coastal plains, some 30-km south-west of Mombasa and just south of Kwale town. The surrounding escarpment rises from around 120 m elevation to c.300 m across the bulk of the plateau, and as high as 450 m at Marare and Pengo Hills. Rainfall ranges from 900–1,200 mm/year, and rivers flowing from the hills supply fresh water to Mombasa and to the Diani/Ukunda area, immediately to the east. The Shimba Hills were gazetted as National Forest as long ago as 1903, being one of the few large areas on the south coast that was still well forested. Grassland areas were incorporated in 1924, and several subsequent extensions took place to bring the reserves to their present size. In 1968, most of the area was double-gazetted as the Shimba Hills National Reserve. Two smaller areas to the west, adjoining the National Reserve and almost entirely forested, remained as Forest Reserves only: these are Mkongani North (1,110 ha) and Mkongani West (1,370 ha). The hills have a heterogeneous mosaic of vegetation, including grassland, scrub and exotic plantations as well as forest. Estimates from aerial photographs suggested that 44% (i.e. 9,500 ha) of the total area was forested, and a further 8,000 ha were forest/scrub formations. Grassland or grassland/scrub covered 3,400 ha, the remainder being plantations (600 ha) and other cover. The hills certainly hold one of the largest areas of coastal forest in East Africa after Arabuko-Sokoke (IBA KE007). At least six major forest types have been described, including tall Milicia forest on the deep soils on the plateau top (in Longomagandi and Makadara forests, and near Kwale town), and on the western escarpment; Afzelia–Erythrophloeum forest, covering much of the eastern and southern escarpment; Paramacrolobium forest on particularly steep scarp slopes to both east and west; and Manilkara–Combretum forest in the lower, western sector of the plateau. The biggest single patch of forest is in the south-western sector, including Mkongani North and West. Further east and north, the forest breaks up into a complex mosaic interspersed with scrub and grassland. Corridors of forest or forest/scrub formations connect most of the forest patches. At least two Kayas, Kwale and Longomwagandi, are situated within the National Reserve. The Kaya forests have spiritual and ceremonial significance to the Mijikenda people of the Kenya coast. A fenced elephant corridor connects the Shimba Hills with Mwaluganji Forest Reserve.
See Box and Tables 2 and 3 for key species. Shimba Hills has a rich coastal forest bird fauna, including three threatened and two restricted-range species. Both Zoothera guttata and Anthus sokokensis have been recorded in Mkongani. Circaetus fasciolatus, Tauraco fischeri and Anthreptes reichenowi are common to fairly common. Sheppardia gunningi is patchily distributed in tall closed-canopy forest, with records from Mkongani (densities estimated as 0.4 territories/ha); Longomwagandi, where it was fairly common in 1992 but not relocated in 1996; and from Makadara. The relatively large area of forest means that populations of most of these species are likely to be viable. In late March and early April, spectacular concentrations of certain Palearctic migrants such as Cuculus canorus and Oriolus oriolus move through on passage. The grasslands hold localized species such as Francolinus afer, Cisticola natalensis and Euplectes nigroventris. These are not species of immediate conservation concern, but grassland is vanishing everywhere in Kenya and the habitat protected in the Shimba Hills is valuable. Regionally threatened species include Hieraaetus ayresii (status unknown); Stephanoaetus coronatus (several pairs probably resident); Erythrocercus holochlorus (fairly common); Pitta angolensis (rarely recorded non-breeding visitor); and Anthreptes neglectus (probably the Kenyan stronghold of this little-known species).
Non-bird biodiversity: Kenya’s only population of the ungulate Hippotragus niger occurs in the Shimba hills, which was the major reason for incorporating grassland areas into the National Reserve. The restricted small mammal Rhynchocyon petersi (EN) also occurs here, together with the distinctive Bdeogale crassicauda omnivora. The forest also holds substantial numbers (c.550 in 1997) of Loxodonta africana (EN). The rare bat Myonycteris relicta (VU) has been collected here. Two frog species, Afrixalus sylvaticus and Hyperolius rubrovermiculatus, are endemic to the Shimba Hills forests and believed to be endangered; the little known and range-restricted Afrixalus changamwensis also occurs. The butterfly fauna is very diverse, with some 295 species (35% of Kenya’s total), including the rare Acraea aubyni and Neptis rogersi, and the endemic Charaxes acuminatus shimbaensis. The flora of the hills is exceptionally rich and important. A total of 1,100 plant taxa are recorded, c.280 of which are endemic to the Shimba Hills area and nearly 20% considered rare globally or in Kenya. This qualifies Shimba as a Centre of Plant Diversity, according to the criteria of the Association pour l’Etude Taxonomique de la Flore d’Afrique. Notable tree species include Diospyros shimbaensis, Cephalosphaera usambarensis, Pavetta tarennoides, Synsepalum kassneri, Bauhinia mombassae, Phyllanthus sacleuxii and undescribed species of Polyceratocarpus and Uvariodendron.
BirdLife International (2022) Important Bird Areas factsheet: Shimba Hills. Downloaded from http://www.birdlife.org on 26/09/2022.