The osprey (Pandion haliaetus) is a fish-eating bird of prey (raptor).
Its success as a predator and the ability to breed in extreme
temperate and tropical climates by migrating in the winter months
has enabled this majestic cosmopolitan bird to range over all
the world’s continents except Antarctica.
Osprey populations found within the Kingdom of Saudi Arabia are
localized along the Red Sea and Arabian Gulf with breeding largely
restricted to islands. Migrating ospreys may also be seen inland
near large sewage pools or reservoirs. Aerial surveys by NCWCD
and records from ornithologists (contained within the Atlas for
Breeding Birds of Arabia) estimate a breeding population of around
350 pairs for the whole Red Sea region. The largest colonies are
found in the Al Wejh and Farasan Islands, both archipelagos maintain
60-80 breeding pairs. The Dahlak Islands off Eritrea and Tiran
Island off Sinai, along with a few other northern Red Sea islands
maintain populations of around 30-50 pairs. A maximum of ten breeding
pairs are known in the Gulf where climate extremes are much greater
and marine flora and fauna less diverse.
The Farasan Islands in the southern Red Sea, located 40 km off
the Saudi Arabian port of Gizan, are recognized by the National
Commission for Wildlife Conservation and Development (NCWCD) and
the World Conservation Union (IUCN) for their diverse marine and
coastal habitats, important for commercial fish stocks, turtles,
cetaceans, dugongs and migratory birds. Protected areas have also
been established on the islands for unique terrestrial fauna such
as the mountain gazelle (Gazella gazella farasani )and the extensive
stands of Avicennia and Rhizophora mangroves. The recent comprehensive
survey of marine resources and the impact of human utilization
of the Farasan Islands Protected Area provides a platform for
developing and integrating other studies to monitor key wildlife
species, and the marine environment as a whole.
The Farasan Islands are thought to hold around 25 per cent of
the total Red Sea osprey population, therefore the Farasan Islands
Protected Area osprey studies which commenced in 1994 are designed
to address three main issues: the status of the Farasan Islands
osprey population, the impact of this species on local fish populations,
and the gathering of baseline data on their breeding biology to
facilitate formulation of management recommendations. Studies
are conducted as a part of an exchange programme involving researchers
from NCWCD and the Manchester Metropolitan University, England,
supported by the British Council. There has only been one other
study of the osprey in the Arabian peninsula region, focusing
on the diet of a resident colony on Tiran Island in the northern
Red Sea.
It is thought that the Red Sea and Gulf breeding populations are
resident, with a small number of over-wintering migrating individuals
from Fenno-Scandinavia. A ringing programme has commenced, using
metal NCWCD and two colour rings (for individual identification
in the field) to attempt to learn more information about their
movements, dispersal and life histories. Records of any sighting
of birds with rings, or individuals found dead should be forwarded
to NCWCD.
Breeding success has not been monitored throughout the Red Sea
region, but recent surveys of ospreys within the Kingdom suggest
that ospreys are vulnerable to the disturbance and demise of breeding
pairs within loose colonies: increased development of the Red
Sea coast and islands are thought to be responsible for this.
Ospreys are particularly vulnerable to disturbance near their
nests from either fishermen using small islands for fishing settlements,
or coast guard patrols. Disturbance at the nest may cause pairs
to abort breeding attempts, particularly during the early stages
of egg laying. Osprey nests should not be visited by the public.
Small mammals such as the natural predator, the white-tailed mongoose
(Ichneumia albicaudia) are also known to predate osprey eggs and
small chicks. Both the white-tailed mongoose and the feral cat
(Felis domesticus) are present on the larger Red Sea islands,
possibly increasing their range by scavenging from garbage tips
and supplementing their diet with birds eggs, chicks and migrant
birds. Avian scavengers such as ravens, gulls and vultures are
not thought to pose a threat to a breeding pair but may take occasional
eggs or chicks on an opportunistic basis.
Until further studies are conducted, it is not known whether Red
Sea ospreys are exposed to chemical pollutants and whether they
might have a detrimental affect on their breeding success.
Ospreys breed in the southern Red Sea from early November through
to May. Most pairs lay eggs from mid-November into December. Ospreys
at more northern Red Sea latitudes generally lay eggs a month
later in early January. It is likely that ospreys have adapted
to breed in the winter months to avoid the extreme summer Red
Sea temperatures and solar radiation, particularly as eggs require
continual incubation and protection from solar radiation. The
higher tides and more favourable southerly currents and winds
in these winter months may also play an important role, particularly
in areas of extensive shallow water, which are often used as hunting
areas by ospreys.
To date, studies suggest considerable variation in the time of
breeding between pairs, separated by as many as 12 weeks within
a colony. This is likely to be attributed to the age and experience
of a pair, nest site availability and, to some degree, courtship
feeding.
The female osprey typically lays a clutch of 2-4 eggs. Long term
studies of breeding pairs have shown that clutch size appears
to be related to the age of the female and experience of the pair.
Fewer larger eggs tend to be laid by older more experienced females.
One egg clutches are rare (probably misclassified due to poor
survey techniques), as is the other extreme of two females sharing
the same nest with two clutches.
The incubation period is around 7-8 weeks, with migratory ospreys
incubating slightly shorter periods on average. Differences are
possibly due to migratory osprey fledglings requiring time to
learn how to capture prey and prepare themselves for their first
long distance migration.
Ospreys are successful because of their ability to adapt toward
variable environmental conditions. This is exhibited in their
breeding strategies which usually incorporate asynchronous egg-laying
and hatching to facilitate facultative brood reduction when food
is unpredictable. Eggs are normally laid 1-3 days apart, with
incubation commencing with the first egg.
This strategy results in chicks hatching at different times, providing
a competitive advantage for the first hatched chick. Facultative
brood reduction (selective chick mortality adaptive to the local
environment) usually occurs when sufficient food is not available
to be fed to all the chicks in the nest. This may be due to adverse
weather conditions preventing foraging for fish, and inducing
starvation or aggression between chicks, or lack of parental investment,
where parental quality is poor.
Nests or eyries are made from a characteristic mass of twigs and
beach litter, often including dead seabirds or other animals picked
from the high tide line. Since the Red Sea coast is typically
of barren sand or rock and sparsely vegetated, most ospreys nest
on the ground, in stark contast to the relatives in colder climes
that nest at the top of tall trees. Ospreys will nest on power
pylons or towers if available near hunting grounds. Red Sea osprey
nests can be over 2 m in height, built over many years. Farasan
osprey nests average about 1.6 m in height and 1.4 m in diameter.
The cup of the nest (usually one per nest) which holds the eggs
is lined with various sea sponges. Each pair has 1-3 nests but
only one is used during breeding each year unless disturbed. The
male uses the nest, along with a courtship display, to attract
a potential mate. Mangrove stands are more extensively distributed
in the southern Red Sea, and occasionaly used as a platform for
an osprey nest.
Alternative nests may be used when nests are occupied by other
birds, following an aborted breeding attempt due to disturbance
or actual predation of eggs or young. Such nests also appear to
be important as roosting sites for individual fledglings whilst
learning to forage and still dependent on their parents. Pair
bonds are commonly maintained for life, up to 15 years.
Incubation is conducted by the male and female, though it is still
unclear why there is so much variation in individual parental
investment between pairs. Fish prey are caught by the male during
incubation and for the first four-five weeks of the chick rearing
period. Both parents usually forage for prey once the chicks are
large enough to fend for themselves, and food demands are greater.
Ospreys exhibit reversed-sexual dimorphism, i.e the female is
larger in body size than the male. This dimorphism is also exhibited
at the chick stage, when females tend to increase in weight more
than males after four weeks old. The chick rearing period is around
50 days. Dimorphism is also shown in colour markings where males
tend to show more white feathers on the breast and neck, providing
greater contrast with the darker flight feathers; most likely
associated with sexual signalling toward females, and used in
conjunction with body postures to warn off other competitive males
or potential predators. Females are more similar in appearance
to feathered nestlings, which may facilitate begging for food
to provision hungry chicks.
Ospreys are restricted to marine habitats as they are the only
diurnal raptor that feed specifically on fish. Most other raptors
feed on smaller birds. Preliminary studies on the Farasan Islands
show that parrotfish (Scaridae), rabbitfish (Siganidae), needlefish
(Belonidae), wrasse (Labridae), and angelfish (Pomacanthidae)
are common prey of the osprey. An osprey, whilst provisioning
chicks, may catch up to eight fish a day, each fish weighing as
much as 800g.
The diversity of osprey fish diet is generally determined by the
type of marine habitat found within the foraging area (usually
close to the nest), where shallow lagoons and gently sloping reef
platforms are favoured over narrow fringing reefs. Studies have
monitored foraging in different marine biotopes (coral, algae,
seagrass, mangrove and sandy substrates), as identified in the
Farasan Islands Marine Management Plan.
A number of the small mangrove islands, free from mammal predators,
with adjacent coral and algae reefs, hold high densitites of breeding
osprey pairs: mangroves are known to be important fish nurseries
for both neighbouring and distant reefs. The NCWCD are presently
engaged in a programme to restore the Avicennia mangroves in Farasan
port area which were damaged due to the construction of a causeway
for sand extraction, limiting tidal flow. Banks are being created
in the causeway to allow the tide to flow into the upper reaches
of the lagoon, and seedling nurseries are being planted to encourage
new growth.
There are still a number of important questions that we would
like to answer to ensure that osprey conservation is managed in
the most effective manner. Where do young osprey go to when they
leave the nest in the spring? Are Red Sea ospreys different in
size and shape and reproductively isolated from the northern temperate
ospreys? Are Red Sea ospreys exposed to chemical contaminants
via the marine environment causing a reduced reproductive effort?
Such questions require long term studies to monitor colonies,
providing opportunities for sharing knowledge, experience and
ideas between scientists and the public, encouraging a greater
understanding of the environment, and awareness of Arabian Wildlife.dency h