Data Zone
Justification of Red List category
This species is considered Endangered because it has a small population size and a very small range, within which its montane forest habitat has been severely fragmented and continues to decline in both extent and quality.
Population justification
Waiyaki and Samba (2000) estimated the population to number 1,400 individuals, which is roughly equivalent to 930 mature individuals. Galbusera et al. (2000) estimated the following subpopulation sizes: Mbololo 1,059, Ngangao 250, and Chawia 38, which totals 1,347 individuals, and c.800 mature individuals. Plot-based Capture-Mark-Recapture models by L. Cousseau (as reported by L. Lens in litt. 2019) on data collected between 2000-2010, and the comparisons of annual survival rates during sub-periods between 2000-2010 with those calculated for 1997-2000, suggest the following rates of decline occurred in each subpopulation between 2000-2010: Mbololo (73%), Ngangao (36%), Chawia (41%). The subpopulation sizes in 2010 may therefore have been more like: Mbololo 289, Ngangao 159, and Chawia 23, which would equate to c.280 mature individuals (L. Lens in litt. 2019).
However, the initial figures by Galbusera et al. (2000) were produced via extrapolation. Hence, these figures assume that densities are constant throughout the whole fragment, which is unlikely due to edge effects and that even in dense homogenous forest, density varies significantly. Additionally, using the CMR models to assess absolute population estimates relies on delicate assumptions. Therefore, there is significant uncertainty around the true population size. To account for this, the population estimate is placed in the band 250-999 mature individuals.
Trend justification
Based on the figures from Galbusera et al. (2000) data from the Capture-Mark-Recapture models (L. Lens in litt. 2019), the subpopulations may have reduced from 1,059-289 (Mbololo), 250-159 (Ngangao) and 38-23 (Chawia). Overall, this equates to an overall population decline of 63.4% over three generations. Hence, the population decline is inferred to fall in the band 60-70% over three generations.
Turdus helleri is confined to three tiny forest patches in the Taita Hills, southern Kenya: Mbololo (c. 200 ha), Ngangao (c.92 ha), and Chawia (c. 50 ha), (L. Lens in litt. 2019).
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 already been cleared in the Taita Hills for cultivation or reforestation with non-native timber. The remaining tiny area was thought to be under serious threat from both clearance and degradation (Brooks et al. 1998, Mulwa 1998, L. Bennun in litt. 1999), however the three segments have been gazetted. Despite this protection, forest loss has been continuing within this species's range, although the loss over the last ten years has been <2% (Global Forest Watch, 2020). 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). Low connectivity of patches can be a problem for this species (Aben et al. 2012), and 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
Clark, J.
Contributors
Bennun, L., Bird, J., Borghesio, L., Ekstrom, J., Evans, M., Githiru, M., Lens, L., Shutes, S., Starkey, M., Symes, A., Ward-Francis, A., Westrip, J.R.S. & Wright, L
Recommended citation
BirdLife International (2024) Species factsheet: Taita Thrush Turdus helleri. Downloaded from
https://datazone.birdlife.org/species/factsheet/taita-thrush-turdus-helleri on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/11/2024.