BLACK HARRIER
Circus maurus
Endangered
Range: Endemic to Namibia and South Africa
Area of Occupancy: 23 024 km2
Population estimate: less than 50 birds, five pairs
Population trend: Fluctuating
Habitat: Desert floodplains, karooid scrub
Threats: No known threats in Namibia
Distribution and abundance
This species is endemic to southern Africa, with the centres of distribution in the
Western Cape and to a lesser extent the Eastern Cape and Free State Provinces of South
Africa (van der Merwe 1981, Simmons 1997). The world population is estimated at less
than 1000 birds (Siegfried 1992). Most of this population occurs in the coastal
(strandveld) areas of the Western Cape, with other breeding birds found in the
mountains and the higher grassland areas of the Eastern Cape and Free State (Simmons
1997, Curtis et al. 2004). This harrier’s range extends into KwaZulu-Natal north of the
Drakensberg and there are scattered records of residents in the Northern Cape and
seasonal (winter) incursions into the southern Kalahari and central Namibia (Simmons
1997). It reaches farthest
north on Namibia's cool
desert coast around the
ephemeral
Haonib
floodplain and Uniab
delta (S Braine and J
Paterson pers. obs.). The
most northerly confirmed
nest sites are 28.5oS near
Royal Natal National Park
in eastern South Africa
(Van Jaarsveld 1986) and
near Kleinsee at 29oS
Black Harrier
(Simmons et al. 2002).
There have been six
Distribution of
birds in Namibia
recorded sightings from
derived from
Botswana, as far north as
SABAP data and
Lake
Ngami
(Penry
wetland counts
1994). It has the most
restricted distribution of
any continental harrier species (Simmons & Simmons 2000), estimated at just over 400
000 km2 (Barnes 2000) and recalculated from SABAP data in Simmons (1997) as 386
750 km2 (Jarvis et al. 2001).
The world population of Black Harriers has been estimated at about 500 pairs (van der
Merwe 1981, Siegfried 1992). It is believed to breed in small numbers (maximum of
five pairs) in Namibia given frequent sightings of immature birds (S Braine, J Paterson
pers. obs.) in the Hoanib and Uniab River deltas, although this has yet to be confirmed.
Immature birds in the grasslands of southern Namibia (Karas region) following good
rains also suggest that breeding may occur there (RE. Simmons pers obs). Densities in
coastal South African regions are higher than anywhere else and its low population is
probably the result of the modification of previously common lowland renosterveld for
agriculture in the Overberg region of the southern Cape (Curtis et al. 2004). Black
Harriers prey predominantly on mice, and their populations are believed to fluctuate
with time as mouse populations fluctuate in response to rainfall. This may explain the
changes reported during the 20th century when it was variously described as going
extinct or common (van der Merwe 1981, Steyn 1982). They are irruptive in the
grasslands of the Free State (B Colahan pers. comm.), and the Succulent Karoo plains of
the Northern Cape with years of abundance often followed by a complete lack of
breeding birds the following year (Simmons et al. 2002). The 5800 km journey of a
satellite-tracked bird breeding in the salt marshes south of Langebaan that moved to
Lesotho (where it over-summered) and back in 6 months, indicates that these birds do
move great distances. On leaving Lesotho in April, the female sampled its previous
breeding area in Langebaan but headed back past Beaufort West to breed in areas of
good rains in the Camdeboo Mountains near Aberdeen, 550 km east (RE Simmons
unpubl data). These data indicate not only the previously unknown migration patterns of
Black Harriers, but also that the population may be smaller than previously suspected.
Ecology
The Black Harrier occurs in coastal areas of Namibia especially the salt-bush vegetation
in the floodplains of the Hoanib and Uniab Rivers, where temperatures are relatively
cool, and small mammal populations sometimes abundant (S Braine pers. obs., J
Paterson pers. obs.). In the Western Cape, this species is mostly found in fynbos
vegetation, especially coastal thicket and mountain fynbos and less often in the lowland
renosterveld and dry restios between these habitats (Simmons et al. 1998, Curtis et al.
2004, Jenkins et al. 2012). In other areas it is found over dry grasslands, road verges,
Karoo scrub and wheat fields (van der Merwe 1981, Steyn 1982).
It forages between one to three metres high over many types of fynbos and grassland
vegetation, especially coastal and mountain fynbos, and less often grain fields and other
modified habitats. Black Harriers specialise in hunting mice by slow quartering and a
lightning strike into short vegetation or in small birds which they catch after a short
chase (Steyn 1982). From records of 138 prey being brought to nests in the Cape
Province the diet comprises mainly mice (72%), birds (25%) and reptiles (3%). These
proportions vary with habitat with montane harriers taking more bird prey (51 percent
of 47 prey items), than coastal birds which take predominanly mice (87 percent)
(Simmons et al. 2002). Diet in Namibia is unknown, but one adult harrier was observed
chasing and catching sparrowlarks (Eremopterix sp.) or Lark-like Buntings (Emberiza
impetuani) breeding in the southern grasslands of Namibia (RE Simmons p;ers. obs.)
Egg-laying peaks in August and September in South Africa (van der Merwe 1981,
Curtis et al. 2004) and they breed at higher densities than casual observations suggest
(10 pairs per 0.7 km2 in the Western Cape, Simmons et al. 1998, Curtis et al. 2001).
There are no breeding records for this species from Namibia (Jarvis et al. 2001), but
sightings of immature birds in the Hoanib and Uniab River floodplains suggest breeding
has occurred in both areas (S Braine pers. obs.).
Breeding success of 1.6 to 2.5 fledglings per pair (Curtis et al. 2004) in South Africa is
higher than that of the African Marsh Harrier (1.1 to 1.6 fledglings per pair: Tarboton &
Allan 1984, Simmons & Simmons 2000), possibly because their ground nests are less
vulnerable to predation in more arid areas, with fewer terrestrial predators.
Birds forage over wide areas covering > 100 km2 and ranging 20 – 30 km from their
nests (RE Simmons unpubl data).
Threats
There are few known threats to this species in Namibia. The small population which
migrates northwards from South Africa covers a wide variety of karooid habitat which
may be overgrazed, especially in southern Namibia. The resident population in the
north-west floodplains occurs within the Skeleton Coast National Park and is thus
protected from cattle grazing and fire.
In South Africa, fragmentation of lowland habitat is the main threat to Black Harrier
populations, but most of the birds found breeding occur in protected areas such as the
West Coast National Park or private reserves (Curtis et al. 2004). Foraging over
wheatfields, which is rare, may expose birds to herbicides and pesticides (as is the case
for African Marsh Harriers Circus ranivorus, de Kock & Simmons 1988) and this may
explain the high incidence of unhatched eggs (18%) and a number of dead adults found
in South Africa (Simmons et al. 2005).
The intense grazing pressure in southern Namibia may isolate the birds found in the
northern regions from the core South African population, but this may have little direct
impact on a migratory species such as this.
Climate change, expected to decrease rainfall over large areas of western Namibia
(Midgley et al. 2005), may reduce the likelihood of favourable conditions for mice and
passerine bird breeding which may in turn reduce the likelihood of harriers breeding in
Namibia.
Conservation status
This species is classified as Endangered because of its very small population of less
than 50 birds in Namibia, and only about five suspected breeding pairs. There is no
indication of decline but, like South African populations, the population fluctuates in
Namibia with many birds in some years and few in others.
It was classified as Near-Threatened in South Africa (Barnes 2000), although it is to be
changed in the 2012 update to Endangered (M Taylor in litt), because of the small
population and declines in the Overberg and other farming areas. It is globally classified
as Vulnerable (Birdlife International 2004). This classification was based on the
assumption that it is heavily reliant on private farmland (in South Africa) making it
susceptible to land-use change. However, about 60% of populations today occur in
protected coastal areas, while many others occur in mountains not under agriculture. It
is the intervening lowlands, comprising renosterveld, and marshy wetlands that have
been largely transformed to wheat lands that has reduced this bird’s population by about
85% in the Overberg and other areas with fertile soils (Curtis et al. 2004). Birds do
indeed forage over these areas but most foraging occurs within natural renosterveld
(Curtis 2005). If renosterveld or core breeding habitats are further fragmented through
agriculture, birds may be forced to forage over transformed habitat and breeding sites
and population size may be further eroded. In Namibia, birds that may be breeding are
protected within the Skeleton Coast Park.
Actions
Monitoring of populations in Namibia's north-western rivers is a priority, especially to
confirm that breeding occurs (probably in October and November). This is best done
when small mammals are abundant and the presence of birds can be checked in other
coastal rivers where extensive Salicornia thickets are present. Breeding birds may be
found to occur in the wetter areas. The distribution of birds that migrate in winter to
central Namibia is poorly known, but the winter habitat may be crucial to the well-being
of the Western Cape core population. Thus, understanding the habitat requirements of
wintering birds and protecting the grasslands or shrublands of the Nama Karoo may
prove to be an important conservation action. Priority should, however, be given to
safeguarding the core populations in South Africa.
Barnes KN (ed) 2000.The Eskom Red data book of birds of South Africa, Lesotho and Swaziland.
Birdlife South Africa, Johannesburg
Birdlife International 2004 Threatened Birds of the World. CD-ROM Birdlife International, Cambridge.
Braine, Steve Personal observation. Naturalist, (hobatere@mweb.com.na)
Colahan, Brian personal communication Ornithologist, Free State Province (colahan@dteea.fs.gov.za)
Curtis O 2005 Responses of raptors to habitat fragmentation: from individual responses to population
susceptibility Masters thesis, University of Cape Town
Curtis O, Jenkins A, Simmons R 2001 The Black Harrier - work in progress. Africa: Birds & Birding 6:
30-36.
Curtis OE, Simmons RE, Jenkins AR 2004 Black Harrier Circus maurus of the Fynbos Biome, South
Africa: a threatened specialist or an adaptable survivor? Bird Conservation International14:233-245.
De Kock AC, Simmons R 1988 Chlorinated hydrocarbon residues in African Marsh Harrier eggs and
concurrent reproductive trends. Ostrich 59:180-181
Jarvis A, Robertson AJ, Brown CJ, Simmons RE 2001. Namibian Avifaunal Database. National
Biodiversity Programme, Ministry of Environment & Tourism, Windhoek.
Jenkins J, Simmons RE. Curtis OE, Atyeo M, Raimondo D, Jenkins AR 2012. The value of Black
Harriers as a predictor of biodiversity in the plant-rich Cape Floral Kingdom, South Africa. Bird Consv
International 2012: 1-12.
Paterson, John personal observation, nature conservator, Skeleton Coast Park (john@paterson.alt.na)
Penry H 1994 Bird atlas of Botswana. University of Natal Press, Pietermaritzburg
Siegfried WR 1992 Conservation status of the South African endemic avifauna. S. Afr. J. Wildl Res
22:61-64
Simmons RE 1997 Black Harrier Circus maurus. In: Harrison JA, Allan DG, Underhill LG, Herremans
M, Tree AJ, Parker V, Brown CJ (eds). The Atlas of Southern African Birds. Vol 1: 241-243. BirdLife
South Africa, Johannesburg.
Simmons RE, Simmons JR 2000 Harriers of the World: their behaviour and ecology. Oxford University
Press, Oxford.
Simmons RE, Curtis O, Jenkins AR 1998 Black Harrier conservation and ecology: preliminary findings
2000. J. African Raptor Biology 13:33-38
Simmons R, Curtis O, Jenkins AR 2002. Third annual report of the Black Harrier Project. Unpublished
Report, FitzPatrick Institute, University of Cape Town.
Simmons RE, Curtis O, Jenkins AR 2005 Black Harrier Circus maurus In: Hockey PAR, Dean WRJ,
Ryan P (eds) Roberts Birds of Southern Africa VII. Pp 502-503 Black Eagle Publishing, Cape Town.
Steyn P 1982 Birds of Prey of Southern Africa. David Philip, Cape Town
Tarboton WR and Allan DG 1984 The status and conservation of Birds of Prey in the Transvaal.
TVL museum Monogr No.3. Pretoria.
Taylor M. (ed South African Red data book). taita@birdlife.org.za
Van der Merwe F 1981 Review of the status and biology of the Black Harrier. Ostrich 52:193-207
Van Jaarsveld J 1986 Black Harrier breeding near Royal Natal Park, RSA. Gabar 1: 27
RE Simmons
Updated by Rob 13 June 2012
Reviewed by: Andrew Jenkins