Justification of Red List Category
Secondary poisoning, trade and persecution are estimated to have caused very rapid population declines in South Africa (listed as EN in South Africa, Lesotho and Swaziland ;and Namibia; Simmons 2015; Taylor and Kemp 2015) and there are anecdotal reports that they have caused declines in other range countries. There is a high probability that such threats and subsequent declines will continue into the future, and as such this qualifies as Vulnerable. In addition, the species' life history strategy (long-lived, slow-breeding) puts the species under greater possible threat of declines. More accurate trend data may become available in the near future and so further reassessment may be required in the future.
The global population size has not been quantified, but the species is reported to be widespread and common but sparse. However, there are fears that Allee effects may occur as a result of fragmentation and unnatural mortalities creating a lag in declines being noticed (L Kemp in litt. 2016). Range wide genetic analysis and population trends analyses are ongoing (L. Kemp. in litt. 2016).
An assessment of the species's status in South Africa (Kemp and Webster in litt. 2008) estimated a 20% loss in the area of suitable habitat within the species's national range in the past 15 years. If this figure is used to project declines into the future, this equates to a population decline of 74% over 94 years (three generations). Although declines are also suspected in other range countries (S. Thomsett and S. Tyler in litt. 2010), there are not thought to be significant declines in Zambia, which may be a stronghold of the species (P. Leonard and L. Roxburgh in litt. 2010). As such, and given that data is currently lacking and that it is difficult to accurately project future declines for such a long-lived species, a decline of 30-49% is projected over 94 years (three generations).
Bucorvus leadbeateri is found from southern Kenya, Rwanda, and Burundi, through south-eastern Democratic Republic of Congo and Tanzania, Zambia, Mozambique and Zimbabwe; south-west to Angola and northern Namibia; and south through Botswana and eastern South Africa, including Swaziland and Lesotho. It is described as widespread and fairly common, and the population in South Africa in 1992 has been estimated at c.1,400 mature individuals - perhaps a 50% decline on historical population numbers (Kemp and Webster in litt. 2008), although certain areas are seeing recoveries due to groups recolonising areas (e.g. Limpopo Valley; Theron et al. 2013). Declines have continued and a reassessment is underway, and assessments in Namibia as well as South Africa, Lesotho and Swaziland, have listed the species as Endangered (Simmons 2015; Taylor and Kemp 2015). Although data for other range countries are lacking, several threats are also thought to be causing population declines in Kenya (S. Thomsett in litt. 2010), Botswana (S. Tyler in litt. 2010) and Zambia (R. Tether, P. Leonard and L. Roxburgh in litt. 2010), though rates of decline in Zambia are thought to be slower than elsewhere (L. Roxburgh in litt. 2010). The Democratic Republic of Congo and Angola are data deficient (L. Kemp in litt. 2016). In Botswana it is still frequent in the Okavango Delta and Chobe areas, where it occurs at higher densities than it averages in South Africa, but is likely to be declining away from protected areas (S. Tyler in litt. 2012).
Behaviour It lives in groups of 2-9 members, rarely 12, and is a co-operative breeder, with the dominant pair assisted by adult, mostly male, and immature helpers to defend a territory and provision a nest (L. Kemp in litt. 2016). The breeding pairs have previously been assumed to be monogamous, but molecular techniques have revealed that extra-pair copulations do occur (Theron et al. 2013). Groups occupy year-round home ranges of 50-100km2, determined primarily by the availability of suitable nest sites and food availability during the dry season (Kemp 2005; Wilson and Hockey 2013). Laying occurs in large cavities in trees, cliffs or earth banks (L. Kemp in litt. 2016), mainly from September to December, with a clutch of 1-3 (usually 2) eggs, although only one survives to fledging (del Hoyo et al. 2001; Chiweshe, Kemp and Webster in litt. 2008). One study in South Africa showed that a family group produced on average only one fledgling every nine years, although birds in the Okavango Delta appear to breed more frequently (del Hoyo et al. 2001; S. Tyler in litt. 2010). Juvenile mortality is reported to be high in a large protected area, and this is likely to be even higher in unprotected areas where anthropogenic threats are present (Kemp 1990). Habitat It inhabits woodland and savanna, also frequenting grassland adjoining patches of forest up to 3,000 m in parts of its range in eastern Africa. The species fares well in protected areas where human threats are excluded and rural areas where cattle assist in maintaining their preferred short grass habitat. If cultural protection is still practiced, the species is productive, but in areas where there is no cultural protection or it has diminished due to the appropriation of Western culture, the species is highly fragmented (L. Kemp in litt. 2016). Diet Its diet is mainly made up of arthropods, and, especially during the wet season, snails, frogs and toads, and sometimes larger prey such as snakes, lizards, rats, hares, squirrels or tortoises. It will on occasion feed on carrion, taking scraps and associated insects. Fruits and seeds are also recorded in its diet, although infrequently (del Hoyo et al. 2001).
A major threat to the species is loss of nesting habitat due to clearance for small-scale use, agriculture, and because of fires and violent storms (L. Kemp in litt. 2016). It can become heat stressed and exhibits heat avoidance behaviour in temperatures above 26oC, and increasing temperatures with climate change could pose a threat (L. Kemp in litt. 2016). Widespread livestock grazing has also lead to the erosion of suitable grassland in Kenya, with perhaps only 10% of suitable habitat remaining in the country (S. Thomsett in litt. 2010). Although cultural beliefs offered some protection in the past in Kenya, recent generations tend not to hold such values, and the species may be directly persecuted as a result (S. Thomsett in litt. 2010). Persecution may occur directly because the species breaks window panes by attacking its own reflection in glass (incurring costs and creating human-wildlife conflict), indirectly by consuming poisoned bait meant for other species, and it is sometimes killed for traditional rituals against drought (del Hoyo et al. 2001; K. Morrison and Y. Friedmann in litt. 2005; L. Kemp in litt. 2016). In South Africa and Zimbabwe, where these beliefs are upheld, there is actually a significant protection given to this species because it has high cultural importance, and these beliefs outweigh any offtake for traditional use (L. Kemp in litt. 2016). Collisions with powerlines may also be a threat in South Africa (K. Morrison and Y. Friedmann in litt. 2005), although only one such mortality has been recorded and more mortalities may occur from electrocution by standing on step-down transformer boxes - especially if an insect nest has been built on or near the box which could act as an attractant for the species (L. Kemp in litt. 2016; R. Little in litt. 2016). Such threats are exacerbated by the slow reproductive rate and maturation, longevity and social structure of the species (S. Thomsett in litt. 2010). This species can be susceptible to Newcastle's Disease Virus (L. Kemp in litt. 2016), and may be under threat from stepping on land mines in areas of conflict (L. Kemp in litt. 2016).
Conservation Actions Underway
It is still protected by tribal lore in many areas, and occurs in several reserves and at least seven national parks (del Hoyo et al. 2001). There is extensive conservation work being carried out in South Africa, including a re-introduction programme, research into several different areas (population dynamics, tracking, and the feasibility of supplementary feeding, multiple clutching, group supplementation, threat mitigation and artificial nest-site provision), public awareness campaigns (A. Turner in litt. 2009), and a Single-Species Recovery Plan, with revision planned for 2017 (L. Kemp in litt. 2016). Areas suitable for reintroduction have been identified (Cilliers et al. 2013); and protocols for reintroduction and hand-rearing have been developed and from 2000-2008 the Mabula Project attempted 13 soft and hard releases and re- introductions of individuals, and a re-introduced female fledged a chick in 2008 in the Mabula Game Reserve (A. Turner in litt. 2009, 2011). However, the challenge remains removing the threats from the habitat with the largest challenge being the extensive abuse of pesticide for carnivore control (L. Kemp in litt. 2016). In the Matobo District of Zimbabwe research is being conducted into emerging threats from small scale farming (L. Kemp in litt. 2016).
Text account compilers
Butchart, S., Calvert, R., Ekstrom, J., Symes, A. & Westrip, J.
Leonard, P., Roxburgh, L., Tether, R., Thomsett, S., Turner, A., Tyler, S., Kemp, L. & Little, R.
BirdLife International (2020) Species factsheet: Bucorvus leadbeateri. Downloaded from http://www.birdlife.org on 07/04/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 07/04/2020.