Archived 2011-2012 topics: Crowned Hawk-eagle (Stephanoaetus coronatus): request for information

Initial deadline for comments: 31 January 2012.

BirdLife species factsheet for Crowned Hawk-eagle

Crowned Hawk-eagle Stephanoaetus coronatus is a widespread resident of sub-Saharan Africa, where it inhabits forest, woodland, savanna and shrubland, as well as some modified habitats such as plantations and secondary growth (Ferguson-Lees and Christie 2001), and can persist in small forest fragments (Dowsett-Lemaire and Dowsett 2006). It is currently listed as being of Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criteria (B and D2: Extent of Occurrence estimated at less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline was not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (A: at least a 30% decline over ten years or three generations, whichever is longer). The population size may be small, but it is not believed to approach the thresholds for Vulnerable under the population size criteria (C and D1: fewer than 10,000 mature individuals with a continuing decline estimated to be at least10% over ten years or three generations, or with a specified population structure).

Concerns have been raised over the conservation status of this species (e.g. Thomsett 2011). Although the species is welcomed by foresters in some areas, it is subjected to a number of significant threats throughout much of its range, including deforestation (carried out for timber extraction, charcoal production, the encroachment of agriculture and plantations, shifting cultivation and mining), competition from humans for prey species (with apparently unsustainable levels of exploitation for bushmeat in some areas), direct persecution in an estimated 90% of its range (e.g. for food, arrow-fletching, witchcraft, ornaments and its pest status and threat to humans) and human disturbance (Ferguson-Lees and Christie 2001, Hockey et al. 2005, Thomsett 2011). This suite of threats implies that the species could be in rapid or fairly rapid decline, especially considering its slow reproductive rate (Thomsett 2011).

In reviewing the literature, Ferguson-Lees and Christie (2001) state that the species is now rare in many parts of West Africa, implying that it has declined in that region. Its range in Malawi is said to be certainly decreasing and habitat clearance there is expected to be impacting the species (Dowsett-Lemaire and Dowsett 2006). It has also declined in southern Mozambique owing to forest destruction along the coast (Parker 1999). The negative effects of habitat loss in South Africa are regarded as being partly offset by the establishment of exotic plantations (Hockey et al. 2005 and references therein).

Ferguson-Lees and Christie (2001) estimate that total the population could number in the upper thousands, although given its range this is perhaps likely to be an underestimate and they also state that, for this reason, an estimate of tens of thousands might be expected. There is thus a strong likelihood that the species’s population approaches as few as 10,000 mature individuals and may even number fewer than 10,000.

Further informative data and observations are requested from all parts of the species’s range in order to aid a review of its threat status. Useful information would comprise indications of changing abundance, habitat trends and the severity of threats, whether local, national or regional in coverage.

If evidence leads to the suspicion that a decline of 20-29% has occurred over the past 56 years (estimate of three generations, based on a generation length of c.18.5 years; BirdLife International unpubl. data) and/or may be projected over the next 56 years, the species may qualify as Near Threatened under criterion A. The species could qualify as Vulnerable under criterion A if it were suspected to have declined by 30-49% over the past 56 years, and/or projected to decline at this rate over the next 56 years. The species could qualify as Endangered if the rate of decline were suspected to be 50% or more over 56 years.

Further information is also sought on the species’s total population size and the likely sub-population structure, i.e. whether all mature individuals probably form one sub-population or, if not, the likely number of mature individuals in the largest sub-population. In terms of the Red List criteria, sub-populations are defined as geographically or otherwise distinct groups between which there is little or no demographic or genetic exchange, i.e. one successful migrant per year or less.

References:

Dowsett-Lemaire, F. and Dowsett, R. J. (2006) The Birds of Malawi: An atlas and handbook. Liège, Belgium: Tauraco Press and Aves a.s.b.l.

Ferguson-Lees, J. and Christie, D. A. (2001) Raptors of the world. London, UK: Christopher Helm.

Hockey, P. A. R., Dean, W. R. J. and Ryan, P. G. (2005) Roberts birds of southern Africa. 7th edition. Cape Town, South Africa: Trustees of the John Voelcker Bird Book Fund.

Parker, V. (1999) The Atlas of the Birds of Sul do Save, Southern Mozambique. Cape Town and Johannesburg, South Africa: Avian Demography Unit and Endangered Wildlife Trust.

Thomsett, S. (2011) Simon Thomsett on the African Crowned Eagle. African Raptors: http://www.africanraptors.org/simon-thomsett-on-the-african-crowned-eagle-part-1/

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10 Responses to Archived 2011-2012 topics: Crowned Hawk-eagle (Stephanoaetus coronatus): request for information

  1. I can comment a bit on this species in Uganda and Rwanda’s forests where we see it occurring in most of the forests of the Albertine Rift but probably at very low numbers in each forest. We don’t know what extent the species can move between forests but there are probably fewer than 5-15 nesting pairs in each of the forests of western Uganda and Rwanda. We have been wanting to radio-tag some individuals to look at movements between forests. These are forests where primate/hyrax densities are high (because they are not eaten here much by people). Although they occur across the Congo basin my guess is that they occur at much lower density there than elsewhere because of the reduced availability of prey.

  2. Joe Taylor says:

    The following comment was submitted on behalf of Derek Pomeroy on 22 December 2011:

    I don’t think we have anything significant in Uganda to add to what is in the [Uganda Bird] atlas

  3. Joe Taylor says:

    The following comments were sent by Françoise Dowsett-Lemaire on 3 January 2012:

    Conservation [status in Ghana:] Threatened by deforestation and hunting, including of its main prey. Surprisingly resilient as still observed in heavily deforested or degraded areas, as in a section of Wassaw F.R. not yet turned into farmland (near Bibiani, pair shooing off a Cassin’s Hawk Eagle, Jan 2009). The old record by Russell (Nkyraa) is in an area now almost totally deforested, and the nearest forest reserve (Bosomoa) has been converted to teak plantations. Protected within the wildlife reserves of Ankasa, Bia, Kakum and Digya.

    For Ghana and even Upper Guinea in general I would consider this eagle as threatened (?Vulnerable? difficult to say). Whether this justifies putting it on a globally threat. list for the whole of Africa is less certain, as its status in Central Africa and countries like Zambia (see Birds of Zambia, 2008) is less worrying.

    On the whole in Upper Guinea the species is decreasing but shows remarkable resilience in places. It is impossible to quantify the % of decrease as we don’t have any detailed records from previous decades.

  4. Anthony Cizek says:

    The general lack of records from the Sul do Save, southern Mozambique (south of the Save R.) (see Parker 1999) needs investigation. This is a very large area – c.1/5 of its “potential” range in southern Africa – and it might be expected throughout.
    Note that the whole of the littoral of Mozambique is classed as part of the “Tropical and Subtropical Moist Broadleaf Forest” Biome by the WWF (e.g. Burgess et al. 2004), and as part of the “Coastal Forests of Eastern Africa” by IUCN/ Conservation International (Burgess and Clarke 2000) yet there were very few records of the eagle from the littoral of southern Mozambique in Parker (1999) – from the extreme north (close to the Save R.) and extreme south (close to South Africa). As a “forest” species it would certainly be expected somewhere in this large region – which because it is classified by these authorities as part of the Forest Biome is considered to be generally vegetated by “forest” (at least potentially) – and its absence is cause for considerable concern. Thus,
    (i) it does not occur here because the habitat is not right,
    (ii) it has been extirpated from a vast area, or
    (iii) it has been overlooked.

    (i) Habitat.
    It is possible that the vegetation of this part of Mozambique is not suitable for the eagle.
    There is much disagreement about the classification of the vegetation of the littoral of southern Mozambique, because much can be classified as “transitional woodland” (to forest, e.g. White 1983) or “thicket”, and it is possible that the southern Mozambique littoral does not warrant inclusion in a Forest Biome, and is on the whole – at the level of the biome – not suitable for the eagle. (There might be some localized patches within the general landscapes though.) Irwin (1981. The Birds of Zimbabwe) notes that “the nest is placed in the central fork of often a very large tree” – and it is possible that many coastal “forest” formations are too short. Coastal forests on the east coast are often short, if very dense.
    Irwin (1981) lists three main types of habitat: (i) evergreen forests in the Eastern Highlands, (ii) riverine forests and (iii) hilly terrain and escarpments (where it occupies even small patches of gully forest, in forest-savanna woodland mosaics). Away from the littoral (specifically), the granite kopje landscapes it favours on and at the edges of the Zimbabwean Plateau generally do not occur in southern Mozambique (which is a sandy coastal plain) and tall riparian/ gallery forest typical of (but highly localised in) south-eastern Zimbabwe and north-eastern South Africa is more limited. But an important evergreen formation is Androstachys johnsonii (musimbiti/ ironwood) groves which can be dense and supports mammals typical of forest formations; e.g. Nyala, Red Duiker, Suni (the eagle is expected to feed on the latter two spp. at least). Msimbiti is not listed by Irwin – and its occurrence in this formation – which occurs (locally) across south-eastern Zimbabwe, north-eastern SA and the Sul do Save needs to be put on record. If it avoids it, why? It is possible that the ironwoods often do not get tall enough to support the eagle’s nest, but do even the largest ironwoods have the right tree architecture for a Crowned Eagle nest?
    Ironwood formations illustrate a more general point: Mucina and Rutherford (2006. The Vegetation of South Africa) classified ironwood formations as Forest sensu stricto, yet they might be too short for the Crowned Eagle (or have the wrong architecture). There are many, many different kinds of dense woody formations on the Sul do Save; which of these are utilized by the Crowned Eagle? So, much work needs to be done to (1) define the vegetation of the Sul do Save – and specifically “Forest” – at fine resolutions, and (2) the habitat requirements of the Crown Eagle there.

    (ii) That said, it is expected somewhere in this vast region – not least because Dowsett et al. 2008 (Birds of Zambia) have it also in “rich miombo”, and dense Brachystegia spp. formations occur across the southern Mozambique littoral – at least potentially. This is the most densely populated part of the Sul do Save and much vegetation has been lost to cultivation. There are other places it might be expected, e.g. the riparian forests along the Save R. in Parque Nacional de Zinave. Its absence is likely at least in part because its habitat has been lost lost (even in the national park) to cultivation and human consumption of its mammal prey.

    (iii) That said, it has also probably been overlooked – as it can be highly localised – and coverage of southern Mozambique is much more limited than in South Africa or Zimbabwe.

    So, much needs to be done to thresh out its status in southern Mozambique. The region is experiencing deforestation rates amongst the highest in the world and the eagle is sensitive to ecosystem changes and is a very good indicator of the status of a number of different kinds of dense woody habitat/ecosystem across southern Africa. The alarm bells are ringing vigorously for its status and the status of dense woody habitats in southern Mozambique.

  5. Ben Phalan says:

    I’ve observed this species in Ghana and Liberia, but have little substantive from my own observations to add to the comments already made.

    However, on the question of prey abundance, Oates et al. (1997) report declines in overall monkey encounter rates (groups detected per km) in Ghana going from 0.50 in 1976 to 0.12 in 1993-96 in Ankasa (a decline of 76%) and from 0.76 – 1.04 in 1977-78 to 0.26 in 1993 in Bia (a decline of 66-75%). Crowned Eagles may have altered their diet to partly accommodate these changes, but the population of this top predator cannot have been unaffected by such a dramatic decline in the prey base (which has likely worsened further since the mid-1990s).

    There may be other literature on declines in other eagle prey species as a result of bushmeat hunting that would be worth looking at (e.g. duikers).

    Reference:
    Oates, J. F., Struhsaker, T. T., Whitesides, G. H. 1997. Extinction faces Ghana’s Red Colobus Monkey and other locally endemic subspecies. Primate Conservation 17: 138-144.

  6. In Gola Forest, Sierra Leone, crowned eagle was considered rare the late 1980s but it was recorded from farmbush as well as logged and primary forest (Allport et al 1989). More recent surveys in the area described it as uncommon but widespread (Klop et al 2008), widespread (Dowsett-Lemaire and Dowsett 2008) or fairly common (Demey 2011). I wouldn’t take this as evidence of population increase but the prey base in Gola has remained firm over this time interval with no evidence of primate declines, for example, within Gola Forest (Lindsell et al 2011) and so I’d feel more confident to say there’s unlikely to have been substantial decline in the forest in the last 20 years. I’ve not evidence from the wider countryside or from other parts of Sierra Leone. In my own experience it is notably less prominent in Gola Forest than in moist forest in western Uganda for example which I’ve often felt surprising, so the suggestion of lower densities in West Africa makes sense to me.

    Allport, G., Ausden, M., Hayman, P.V., Robertson, P. and Wood, P. (1989). The conservation of the birds in Gola Forest, Sierra Leone. Cambridge, BirdLife International.

    Demey, R. (2011). Ornithological survey of the transboundary area Sierra Leone / Liberia of Gola Forest.

    Dowsett-Lemaire, F. and Dowsett, R.J.D. (2007). Faunistic survey of Gola Forest (Sierra Leone) in January-February 2007, with an emphasis on birds.

    Klop, E., Lindsell, J.A. and Siaka, A. (2008). Biodiversity of Gola Forest, Sierra Leone, RSPB and CSSL.

    Lindsell, J.A., Klop, E. and Siaka, A.M. (2011). The impact of civil war on forest wildlife in West Africa: mammals in Gola Forest, Sierra Leone. Oryx 45(01): 69-77.

  7. Joe Taylor says:

    The following comments were sent by Neil Baker on 19 January 2012:

    . . . doing OK in Tanzania, I think but we do not really know.

    there are still large blocks of montane forest that support healthy populations of monkeys and vervets are widespread and locally common throughout the woodlands that this bird inhabits at lower densities. the smaller duikers do well in many areas (despite the bush meat trade) and there are other critters that this bird will take . . .

  8. Philip Hall says:

    There are no accurate population estimates for NIgeria although it seems likely that the population has been impacted by the widespread forest clearance in the south of the country. In the SE where the main block of forest remains in the Cross River National Park, it appears to be widespread but uncommon. Elsewhere, breeding was confirmed in Okomu National Park in 2010 and in the 1990s. there was a record of a breeding pair in the NIger Delta. With the intensification of oil activities in the Niger Delta, there is every likelihood that the species has now been extirpated in the area so in all probability, the only chance for its survival in Nigeria lies in the Cross River National Park.

  9. Joe Taylor says:

    The following comments were sent by David Ewbank on 25 January 2012, regarding the species’s status in Zimbabwe:

    most of the distribution loss is in the higher rainfall northeast of the country. I was living in the southwest near the Matobo NP where the number of known nests has actually increased – whether this is more searching or a real increase is unknown. this eagle occurs in better quality woodland: the range loss is mainly in Brachystegia which has been largely converted to farmalnd which often leads to loss of large trees for nesting. the prey of this bird has not been studed in this area.; elsewhere in Zimbabwe gamebirds & mammals are taken. these often decline with the large biomass of livestock present in the communal areas & to some extent in the commercial farms.
    This have been critisced on the grounds that many of these eagles are around according to Recent Reports in Honeyguide & according to the Atlas of Southern African Birds (in the 1980s). But there are many reports of declines as well for bataleur & tawny eagle eg recent reports Honeyguide 39(4); 204 reports most recent highveld records of tawnies likely to be steppe or lesser spotted eagles. Presence is not necessarilty indicative of breeding as there’s a report in Recent Records Honeyguide 43: 123 of Crowned Eagle being present at a site for 20 years but no breeding recorded.

  10. Joe Taylor says:

    The following comments (originally made in October 2010) were sent by Trevor Jones on 26 January 2012:

    Crowned eagle in Udzungwa:
    Good density of breeding pairs (and high density of monkey prey in particular, all four diurnal species of which I’ve seen them hunting) in Mwanihana forest, in the UMNP: based on 3 nests that I know of in area of ~30km2, there could be 15-20 pairs.
    Also in Luhomero-Ndundulu, several pairs, 250km2 of forests therefore maybe 20 pairs again (also small Cassins population though maybe not too much competition?). ACE feed primarily on the tree hyrax, in my experience. (This is most common prey item found below nests in Mwanihana too).
    Few pairs scattered round other forests, e.g. Nyumbanitu, Ukami, Iwonde, Iyondo, Matundu… (maybe none breeding in Uzungwa scarp, Kising’a-Rugaro, New Dabaga, because so much prey hunted out by humans), thus I would guess at about 50 pairs throughout Udzungwa.
    But in my experience, they breed only every two years.
    Of course, this is a STRONGHOLD – probably best density in Tanzania?

    Totally opposed to any capture or export of this species which must be NATIONALLY vulnerable, considering their requirements and decreasing availability of large forests with large prey base.

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