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The African Marsh-Harrier is endemic to
Africa and is mostly found in the coastal and upland wetlands of
KwaZulu-Natal. They are also found in wetter areas of South Africa’s fynbos
biome around large reed-fringed lakes.
In South Africa it is almost entirely
absent from areas with rainfall below 300 mm. This, combined with the range
of its main prey, Striped Mice - Rhabdomys pumilio, explains much of
its present distribution. Historically its range was probably larger, with
birds reported from many more wetlands in KwaZulu-Natal and the Nama Karoo
than presently found.
The population is South African is
thought to have declined, with numbers estimated to be only 3000-5000 pairs.
However, the only really accurate figures are 500-1000 pairs estimated from
the Mpumalanga. In places it reaches high densities of 8 pairs/10 km2
but its core reed beds have never been accurately surveyed. Where wetlands
have been degraded, drained or converted to agricultural land the bird has
disappeared. Its population may naturally fluctuate in core areas as rodent
populations fluctuate with rainfall.
Bird Atlas data indicates no substantial
movements, but greater conspicuousness in the Okavango during early breeding
-probably due to displaying birds being more visible, but Southern Cape
birds do move for short periods between breeding seasons. A slight increase
in sightings in the Gauteng and KwaZulu-Natal occurs in midsummer (December
to February) which is possibly due to immature birds disperse to these
areas.
The African Marsh-Harrier is almost
exclusively a denizen of wetlands, particularly large inaccessible
marshlands such as the Okavango Delta, coastal wetlands and (further north
in Africa) highland wetlands. They may however, nest in small wetlands (1-2
ha) as long as suitable foraging grounds occur nearby. They nest commonly in
flooded reed, phragmites and papyrus beds, but forages outside wetland
habitat over drier flood plains, grasslands and fynbos, particularly along
borders and eco-tones. In the Southern Cape they are frequently seen over
agricultural grain fields hunting mice and birds. They are also
occasionally seen over open water or over the canopy of woodland hunting
fish/frogs and birds respectively.
The birds are usually solitary except
when breeding - then several birds may be seen foraging over wetlands and
small clumps of breeders occur together. They are often first glimpsed
foraging slowly just above wetland vegetation, but soon lost to site as it
covers large distances. Displaying birds often soar high over their breeding
grounds and they may be detected by their calling as they descend over their
nesting area. However, like most harriers they are typically silent and
elusive. The greatest foraging activity occurs on blustery days, while
midday sees a significant increase in display activity.
The African Marsh-Harrier, like all
harriers, is known for their aerial food passes. The male calls softly as
they approach incubating or brooding females. The female flies under the
prey-carrying male and catches the prey in mid-air. Prey is missed only
about 4% of the time, similar to other harriers. Harriers in wet habitats
undertake fewer aerial passes (49% of 305 for African Marsh-Harrier) than
those in dry habitats. Birds are highly territorial during breeding but less
often interact while foraging away from the nest. Territoriality is
typically intra-sexual and is characterised by leg-lowering and parallel
flying between birds; this is common in other harriers, except Black
Harriers. Birds rarely physically hit each other and birds grasping talons
cartwheel to the ground in the most serious territorial intrusions.
African Marsh Harriers forages between
1-3 m high over many types of reeds, phragmites and floodplain grassland
vegetation. They fly between 20 km/hr and 29 km/hr depending on wind
strength (slower in stronger wind). As the smallest marsh harrier, the bird
is a buoyant flier, with a typical flap-sailing flight, occasionally
interspersed with hovering if prey is sensed. It flashes fast into the
vegetation to strike at small mammals and may hover over unseen prey waiting
for it to flush and may chase birds as they flush. In most instances birds
are hunting for small mammals especially Striped Mice - Rhabdomys pumilio
and Vlei Rats - Otomys irroratus. Other prey includes passerines
and water birds (23% of 374 items) frogs (2%) and fish (1%). Their foraging
success for mammals is significantly higher (41% of 58 attempts) than
success in chasing birds (13% of 24 attempts). Predation success is related
to vegetation depth (higher in shorter grass) and not to habitats where prey
is most abundant (dense vegetation). Adults are naturally much more
successful hunters than immatures (55% vs. 11% success rate), and immatures
often chase inappropriate prey and make multiple attempts at prey that are
clearly aware of their presence.
While seen as a weak flier, African
Marsh-Harriers cover large distances during foraging; up to 200 km when
foraging for demanding nestlings or between 38% to 50% of the daylight
hours. They have been found to synchronise their foraging with the activity
of their chief prey: both peaked at 10h00 and 15h00 in the Southern Cape. At
these times adult harriers return more prey to the nest than at other times.
It has been found that significantly more prey is brought to nests during
strong wind and under cloudy skies than under calm conditions and clear
skies. They have also been observed to sometimes forage over open water
looking for frogs or carrion such as dead fish.
They Marsh-Harrier is a monogamous
breeder. Their favoured breeding habitat includes the large reed beds which
fringe lakes or floodplains. Less commonly they are found breeding in short
sedges, coastal lagoons or rarely in fynbos, close to large wetlands.
Unfortunately these habitats are under severe threat from reclamation for
agriculture. Like other Harriers, mate fidelity is high - pairs tend to stay
together and often retain same territory and nest in the same general
location year after year. Extra-pair copulations are rare comprising about 2
% of all copulations and probably not resulting in extra-pair
fertilisations. Mate guarding and high frequency of copulations ensure
monogamy. Males, and less frequently females display over potential sites
by sky-dancing in a series of ‘U’ shaped undulations.
This is an advertisement against intrusion by other males and
simultaneously attracts females. This behaviour is especially common among
unmated males. |
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Males in better condition tend to display more often than
poor conditioned males. Where they breed close to Black Harriers,
inter-specific interactions occur frequently.
September seems to be the peak
egg-laying month in South Africa (38% of 123 records) - much longer than
temperate zone harriers. In South Africa (where rainfall is evenly spread)
minimum temperature rises coincides with first nests appearing. Ultimately,
the breeding season is timed such that peak nestling demands coincide with
peak prey availability and prey intake.
As with other harriers, they male
typically begins the nest building with twigs. Building is taken over by
the female who carry stems and later grasses to the nest. The male may
contribute grass or stems to the nest when guarding eggs or chicks while the
female is away eating. The nest is a medium to large structure of grasses
and reed stems underlain by twigs, about 45-90 cm across usually placed in
reeds typically over water or near water. In thick emergent vegetation
nests may be built up to 2 metres above the water.
Normally 2-5 eggs are produced, with an
average of 3 eggs. The eggs are similar in shape to chicken eggs. Freshly
laid eggs are light bluish-white, turning white and becoming stained during
incubation. Very rarely eggs are lightly speckled with brown flecks. Eggs
are laid at widely varying intervals, the average of 2 to 3 days apart.
Unlike most other large species, the first eggs are smaller than the last
egg.
Young hatch with white down, pink skin
and eyes initially closed, weighing about 22 g. Asynchronous hatching is
common with the first 2 young often hatching within 1 day of each other or
together, last hatchlings are sometimes up to 8 days behind. The last chicks
are first to succumb if food becomes scarce. The first (brown) feathers
begin to appear at about 14 days on the wing, followed by the tail then the
body.
Adult females are very attentive in
brooding and feeding. At about 20 days the young start to defend themselves
and by about 4 weeks old they are mainly brown feathered and hide in runnels
in the surrounding vegetation. The nestling period until first flight is
around 41 days with variation dependent upon sex and condition. Females are
normally heavier at fledging than males and have darker chocolate brown
eyes.
Nestlings disturbed on the nest lie on
their backs and strike with their feet. Adults rarely mob humans who get too
close, but will drive off birds of prey, (especially African Fish-Eagles)
and dive at mongooses. Time until independence varies from 74-90 days after
hatching, when parents stop feeding young but do not drive them from their
territory. Flying young gradually begin hunting on their own while waiting
for ever-decreasing food provisioning.
Like the Black Harrier, African
Marsh-Harrier has recently been elevated to a species of conservation
concern following the realisation that its wide distribution hides the very
low density at which it occurs. There is no doubt that it is threatened by
habitat loss and degradation, but the extent is hard to gauge. Threats in
South Africa are listed as habitat loss and fires during breeding, and
vulnerability to land use changes. It is now classified as Vulnerable due to
a suspected 20% decrease and loss of wetlands. Degradation (rather than
loss) of this habitat is the most insidious factor diminishing population
size since many wetlands remain intact in Gauteng but no longer support
harriers. Pesticides are known to occur in eggs but there was no apparent
influence on the output or adult survival.
The female is almost a third larger than
male. This is a medium to large, brownish-orange bird speckled with white,
especially on the leading edge of the wing. Overall the female is slightly
darker brown and more rufous than the male. All males, particularly older
ones, have grey on the tail and windows of the wings.
Adult birds have bright yellow eyes.
Both sexes’ underwings are barred and the primary tips are a dark brown.
Adults have an owl-like ruff on the face which is apparent at close
quarters.
Juveniles are a dark chocolate brown
often with a pale chest band and yellowish-white on the patagium and
sometime on the head. Chicks are born with white down, pink skin and eyes
are initially closed. Their second down is a more yellowish white and the
first feathers are a dark brown.
Immature birds look more like the
adults, but retain dark secondaries - especially prominent on the underwing
and have a light breast band which is more prominent than in adults. They
also have dark brown eyes as opposed to the bright yellow eyes of the
adults. Male birds’ eyes turn yellow sooner than the females.
The Black Harrier is sometimes confused
for the African Marsh-Harrier as at a distance Black Harriers fly in a
similar flap-sail fashion but appear more buoyant and has shorter wings but
a longer tail. The African Marsh-Harrier has a similar voice but the Black
Harrier is less strident.
Young African Marsh-Harriers are easily
confused with the Western Marsh-Harrier but for the non-barred tail and no
barring under the wing whereas the juvenile Marsh-Harrier always have
barring on the tail and underwing.
Their most frequently heard call is the
whistling for food or solicitation call, psiew-psiew-psiew of the female.
The alarm call is given while defending the nest and a chattering
tchak-tchak-tchak. Males have a higher frequency than females and are more
strident than the Black Harrier. A high squealing woeeep is uttered by a
displaying male at the top of their ‘U’ shaped sky-dancing displays during
courtship. A soft prrduk contact call is uttered by both males and females
before passing food. The juvenile’s food call is a high-pitched version of
the adult female’s psiew call. |
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