VU
Pemba Green-pigeon Treron pembaensis



Justification

Justification of Red List Category
This species is listed as Vulnerable because it has a single small population which is suspected to be declining as a result of habitat loss and degradation, owing primarily to a local agricultural trend away from plantation crops and towards open farmland. It has been suggested that the species is much rarer than currently assumed, and if this is confirmed the species may be uplisted to a higher threat category.

Population justification
Recent visitors to Pemba have struggled to find this species, which now appears to be rather rare (A. Sander in litt. 2004, M. Virani in litt. 2005, J. Wolstencroft in litt. 2005, 2007, N. Burgess in litt. 2012). Population estimate = 5-8 individuals/km2 × 400 km2 (45% of EOO) = 2,000-3,200 individuals (density range from up to lower quartile of six congeners in BirdLife Bird Population Density Spreadsheet). Perhaps best placed in the band 2,500-9,999 mature individuals at present: this estimate requires validation, and direct information on area of suitable habitat, population densities in various habitats, and total population size may lead to adjustment of this estimate up or down. The estimate equates to 3,750-14,999 individuals, rounded here to 3,500-15,000 individuals.

Trend justification
Loss and degradation of both primary and secondary habitat is occurring (A. Hija in litt. 2005, Virani 2005, M. Virani in litt. 2005, J. Wolstencroft in litt. 2007), with Zanzibar's (Pemba and Unguja) forest declining at 1.2% per year (Siex et al. 2013). This is likely to decrease densities of this species at a slow rate (Catry et al. 2000).

Distribution and population

Treron pembaensis is endemic to Pemba and adjacent offshore coral islets, some 55 km off the coast of northern Tanzania. Although occurring over most of the island, it is most common in the two small remaining native forests; Ngezi (14 km2) and Msitu Mkuu (3 km2) (Catry et al. 2000). Given the rarity of the species within its range (A. Sander in litt. 2004, M. Virani in litt. 2005, J. Wolstencroft in litt. 2005, 2007), the global population size is believed to be fewer than 10,000 mature individuals, although it has been suggested that the total population may actually number fewer than 500 individuals (J. Wolstencroft in litt. 2007). Global population trends have not been quantified, but populations appear to be declining slightly owing to slow habitat conversion.

Ecology

This species occurs in a number of forested habitats, including secondary growth, clove plantations, and gardens, but is much more common in native, primary forest. It feeds on a variety of fruit high in the canopy. Breeding has been recorded from October-February, with nests found even near human habitation or in plantations (B. Peters in litt. 2005). The flimsy nest platform is made of twigs, and contains one or two eggs.

Threats

Decreasing world clove prices led to the conversion of some old clove plantations (which offered suitable habitat) to open farmland growing rice and cassava (Catry et al. 2000, Virani 2005, M. Virani in litt. 2005, J. Wolstencroft in litt. 2007). Low-statue coral rag woodland, marginal agricultural land and dry scrub are also being cleared for cultivation (J. Wolstencroft in litt. 2007). Wooded knolls and extensively managed plantations, where the species could occur, are in decline (J. Wolstencroft in litt. 2007). The human population of Pemba continues to rise (400 individuals/km2, and increasing by 5% per year [Siex 2011]), and although agriculture remains small-scale the need for crop-land is intensifying rapidly (J. Wolstencroft in litt. 2007, N. Burgess in litt. 2102). The vast majority of the human population is dependent upon shifting cultivation and forest products, such as building poles, firewood, and charcoal. Due to the high price of electricity, even the urban population is heavily reliant on firewood and charcoal for cooking, and Zanzibar as a whole is losing an estimated 1.2 percent of its forest each year, leading to increasing fragmentation and rapidly diminishing any potential to maintain and restore connectivity of forest patches (Siex 2011). Some native forest has also been converted to rubber plantation (Virani 2005). Ras Kiuyu forest has been heavily exploited for building materials, lime burning and fuel wood (A. Hija in litt. 2005, N. Burgess in litt. 2012). Msitu Mkuu Forest Reserve is subject to illegal exploitation (A. Hija in litt. 2005, N. Burgess in litt. 2012). Non-native House Crows Corvus splendens may also predate nests (F. Reid in litt. 2005).

Conservation actions

Conservation Actions Underway
Protected areas on Pemba include Ngezi-Vumawinbi Nature Reserve, Msitu Mkuu Forest Reserve and Ras Kiuyu Proposed Forest Reserve (Siex 2011). There are also 13 community forests which include high protection and low impact use zones (Siex 2011).

Conservation Actions Proposed
Conduct surveys to assess its population size. Once a baseline estimate of the population size has been obtained, continue to monitor population trends. Monitor rates of habitat loss and degradation. Combine research into habitat loss and population trends with in-depth ecological studies of the species. Control illegal activities within the Forest Reserves (A. Hija in litt. 2005). Improve sustainable tourism facilities at Ngezi Nature Reserve (N. Burgess in litt. 2012). Protect additional areas of forest and off-shore islands (J. Wolstencroft in litt. 2007). Encourage the planting of suitable fruiting trees, especially in tourist areas (J. Wolstencroft in litt. 2007). Promote sensitive tourist development (J. Wolstencroft in litt. 2007). Carry out survey work to determine if there is potential to restore connectivity of forest patches via enrichment planting (Siex 2011).

Identification

25 cm. Smallish, arboreal, pigeon. Adults are dull green with grey head, neck and underparts, large purple shoulder patch, and scalloped green-yellow, chestnut, and cream-coloured vent and undertail coverts. Immatures are duller and lack shoulder patch. Similar spp. None in range. Voice Similar to African Green-pigeon Treron calva, but slightly softer. The three- or four-part call consists of a series of fluty whistles or trills, interspersed with grunts and growls. Also a rather quiet cluck.

Acknowledgements

Text account compilers
Butchart, S., Ekstrom, J., Khwaja, N., Pilgrim, J., Robertson, P., Starkey, M., Symes, A., Taylor, J., Westrip, J.

Contributors
Burgess, N., Hija, A., Virani, M., Reid, F., Wolstencroft, J., Sander, A., Peters, B.


Recommended citation
BirdLife International (2019) Species factsheet: Treron pembaensis. Downloaded from http://www.birdlife.org on 25/04/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/04/2019.