Justification of Red List Category
This species is considered Critically Endangered because it has a tiny occupied range of c. 3.5 km2, within which its montane forest habitat has been severely fragmented and continues to decline in both extent and quality.
Waiyaki and Samba (2000) estimate the population to number 1,400 individuals, roughly equivalent to 930 mature individuals.
The population is suspected to be in decline as the species's montane forest habitat has been severely fragmented and continues to decline in both extent and quality, however the rate of decline has not been quantified.
Turdus helleri is confined to four tiny forest patches in the Taita Hills, southern Kenya: Mbololo (c. 200 ha), Ngangao (c.92 ha), Chawia (c. 50 ha) and Yale (2 ha) (Brooks 1997, Brooks et al. 1998, L. Bennun in litt. 1999, Waiyaki and Samba 2000). Although there have been reported sightings at Mt Kasigau, 50 km south-east of the Taita Hills, survey work in 1998 did not record the species there (Brooks 1997, Barnes et al. 1999). Research in 1997 indicated a total population of c.1,350 birds, with c. 1,060 in Mbololo, 250 in Ngangao and 38 in Chawia (Galbusera et al. 2000, Waiyaki and Samba 2000, Waiyaki et al. 2001), although the effective population size is likely to be lower owing to a male-biased sex ratio. In 2009 and 2015 surveys confirmed continued presence of the species in Mbololo and Ngangao fragments (M. Githiru in litt. 2008, 2009, 2010, L. Borghesio in litt. 2016).
It is confined to montane cloud-forest (Waiyaki and Samba 2000), not venturing into secondary growth, scrub or cultivated areas (Zimmerman et al. 1996), although the areas where it occurs have been heavily logged in the past (Brooks 1997). Despite much research, very few inter-fragment movements have been recorded (Waiyaki and Samba 2000). It prefers well-shaded areas with a dense understorey, high litter-cover and little or no herbaceous cover (Waiyaki and Samba 2000), and consequently is found at greater density in Mbolobo, the least disturbed forest area, and is rarest in Chawia, which has a more open canopy and a very shrubby understorey (Brooks 1997, Waiyaki and Samba 2000, Waiyaki et al. 2001). It rarely ascends more than 2 m above ground (Zimmerman et al. 1996), although nests can be up to 10m high (L. Borghesio in litt. 2016). At certain times of the year its diet is predominantly fruit, but it will also eat invertebrates (Brooks 1997, L. Borghesio in litt. 2016). It is monogamous and terrestrial, with overlapping home ranges (Waiyaki and Samba 2000) and breeding between January and July (although this may be variable as limited data from work in the region in 2000 and 2015 suggest breeding September to March [Samba et al. 2003, L. Borghesio in litt. 2016]). The clutch-size is 1-3 (Urban et al. 1997). Orange Ground-thrush Zoothera gurneyi often occurs in exactly the same areas as T. helleri (Brooks 1997).
Most indigenous forest has been cleared in the Taita Hills for cultivation or reforestation with non-native timber, and the remaining tiny area is under serious threat from both clearance and degradation (Brooks et al. 1998, Mulwa 1998, L. Bennun in litt. 1999), and the low connectivity of patches can be a problem for this species (Aben et al. 2012). However, habitat quality in the largest two forest fragments remains good (Waiyaki and Samba 2000, Rogers et al. 2008). A highly male-biased sex ratio in Chawia (only 10% of birds were female) might have significant negative consequences for the subpopulation's long-term survival (Lens et al. 1998, Waiyaki and Samba 2000, Waiyaki et al. 2001). The species's reproductive rate may thus be lower than expected (Lens et al. 1998). Inbreeding is a concern due to a lack of movement of individuals between forest fragments (Collar 2005). Where habitat disturbance leads to deteriorations in body condition, the long-term survival of sub-populations may be put at risk (Lens et al. 2001, 2002). Other threats include fire, growing evidence of high rates of nest predation (L. Borghesio in litt. 2016), and climate change.
Conservation and Research Actions Underway
A Darwin Initiative project has been set up in the Taita Hills, and as part of this an international Species Action Plan has been developed (A. War-Francis in litt. 2014, Nature Kenya et al. 2015). The Forest Department is now safeguarding the remaining forest fragments of the Taita Hills, which have been designated as an IBA. Much of the remaining forest habitat is formally protected and managed by either the Kenya Forest Service or the County Government (A. Ward-Francis in litt. 2016). At present, efforts are being undertaken (ban of cattle grazing, enrichment planting with seedlings) to reduce habitat degradation and restore indigenous forest fragments in Chawia; while it remains to be seen what affect this has on the thrush population, unringed juveniles have been seen.
As part of the BirdLife Preventing Extinctions programme for this species and Taita Apalis, the following actions have been planned or are being implemented:
1. Working to engage critical local stakeholders in the restoration of exotic plantations back to native forest, through selective clearance of exotic vegetation. This is targeted in priority areas for increasing connectivity, including around Ngangao and Vuria (A. Ward-Francis in litt. 2016). On adjacent agricultural land, fast-growing non-native species will be planted to provide a buffer zone.
2. Income-generating activities, including bee-keeping and butterfly-rearing, have been initiated and farmers have been educated in environmentally responsible agricultural practices.
3. In order to secure the long-term survival of the Chawia population, a translocation has taken place.
4. Nature Kenya has initiated the development of local capacity through catalyzing the formation of a Site Support Group (SSG) with the aim of enabling local people to constructively engage in conservation of the IBA (M. Githiru in litt. 2008, 2009, 2010), which recently included the development of a community resource centre in Ngangao (A. Ward-Francis in litt. 2016).
5. Led by Nature Kenya, supported by the World Land Trust, Rainforest Trust, Royal Society for the Protection of Birds and the African Bird Club, 6.28 ha of land has been secured so far to allow for the protection of remaining native vegetation, through land purchase and leasing, focussing on privately owned plots in the Vuria corridor.
20-22 cm. Medium-sized thrush of montane forest. Dark upperparts, head and breast. White underparts. Rich rufous flanks. Bright orange bill and eye-ring. Voice Thought to resemble Olive Thrush T. olivaceus. Hints Shy, keeps well hidden in dense thickets and undergrowth, where spends much time foraging in leaf-litter.
Text account compilers
Bird, J., Ekstrom, J., Evans, M., Shutes, S., Starkey, M., Symes, A., Wright, L & Westrip, J.
Bennun, L., Githiru, M., Lens, L., Ward-Francis, A. & Borghesio, L.
BirdLife International (2019) Species factsheet: Turdus helleri. Downloaded from http://www.birdlife.org on 10/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 10/12/2019.