The magnificent, and totally unique species, the Osprey (Pandion haliaetus), are a medium to large sized raptor, some 55 to 65 cm in length, with a wingspan ranging between 1.5 to 1.7 m. Their long wings are characteristic, due to a bend at their carpal (wrist) joint – a distinguishing feature whilst in flight, from that of the straighter winged ‘sea eagle’. They are sometimes referred to as a ‘sea hawk’, ‘fish eagle’, ‘river hawk’ or ‘fish hawk’. They weigh generally 1.0 to 1.1 kg for adult males, and, 1.2 to 1.9 kg for adult females.
They are a fish-eating bird of prey.
Their underbellies are bright white with a mottled, dark brown band around their upper chest, like a necklace. Their white heads also have a distinctive black strip that extends across their eyes and down the side of their faces. Other identifying markings include a dark stripe through each eye, a dark brown back, a black beak, and, their feet are a pale blue-grey colour.
Where are they found in Australia?
In Australia, Ospreys are generally found in the northern coastal areas, from Broome in Western Australia, across to the south coast of New South Wales. A southern population inhabits from Kangaroo Island in South Australia, westward to the Great Australian Bight. In Western Australia, another population can be found in the region of Esperance all the way northward to Cape Keraudren.
Diet & Characteristics
Ospreys are unique to any other bird of prey. There is no trace of a common ancestor – dating back some 15 million years. They are the only raptor to eat fish alone and have evolved to be superbly suited to the task.
Fish make up some 99% of the Osprey’s diet. They are uniquely adapted to their dietary habits – both physically and behaviourly. As a result of these unique characteristics, they have their own taxonomic genus, ‘Pandion’, and family, ‘Pandionidae’.
Their vision has been adapted to detecting underwater objects from the air. They first sight their prey as they glide over the water at a height of 10 to 50 m, they then tend to hover momentarily, as if to calculate the movement of their prey → then plunge, feet first, into the water and grab the fish with their talons. They then immediately take off, from the water, with their powerful wings.
They have relatively long, legs for a bird of prey. Unlike all other birds of prey, their toes are all of equal length. The Osprey’s large, scaly feet have sharp little spines (spicules) beneath their talons which, together with their long, sharp, curved claws and reversible outer toe, helps grip the slippery fish. Their specialised gut comes with strong enzymes which can quickly break down and absorb their fishy meal – even the bones . . .
The Osprey’s feathers are dense and oily to deflect water. An oil gland situate at their rump, at their tail feathers, produces oil which the Osprey spreads around its feathers by rubbing and preening. It acts as both waterproofing agent and as an anti-parasitic.
Their nostrils are also unique to the Osprey, being long and slit-like rather than round. Their nostrils can be closed when underwater thereby preventing water from entering their nasal passages.
Once their prey is secured, they take their catch to shore – either into a tree or tall structure, or sometimes even on the waters edge. There, they can savour their meal. They generally take fish that are between 25 to 35 cm in length, however, they have been recorded catching fish from anything between 50 g to 2 kg in weight !!! The latter would be quite a weight to draw out of the water . . ..
An Osprey can live up to 25 years of age, however, in the wild, usually around 10 to 15 years.
They tolerate a wide variety of habitats – all they need is a safe nesting site, shallow water and an abundant supply of fish. They are found on all continents except Antarctica.
Ospreys generally nest within 3 to 5 km of a water of body. They choose tall structures that can support their large, bulky nests of some 1 to 1.5 m in diameter – and safe from ground-based predators. Young Ospreys resemble adults, but are usually more ‘speckled’ in appearance and have a less well-defined ‘necklace’. They also have an orange-red Iris – as they mature it becomes yellow. The adult plumage is usually established by the time they are 18 months old.
Ospreys are generally monogamous. There are rare occurrences, when the nest sites are so close together, that a male may defend two nests. In such cases, the first nest usually experiences a higher reproductive success as the male devotes more resources to that nest. Courtship centres around food and nest sites. Male Ospreys are known to perform conspicuous aerial displays, near the nest site – usually during early courtship. This is believed to serve to attract potential mates as well as threaten an potential intruders. Both males and females collect materials for the nest, but the female does most of the arranging of the nest. The nest is typically constructed of sticks, and lined with softer materials such as seaweed, kelp, grasses or even cardboard. Osprey couples use the same nest year after year . . .
Two to four eggs are laid over a period of several days, each 1 to 2 days apart. The eggs hatch after approximately 40 days. When the chicks hatch, they are covered in white down, with brown streaks on the face, back, and wings. At some 10 days of age, this down is replaced by charcoal-colored down.
The Osprey chicks spend their first 7 to 8 weeks of life confined to the nest. The mother will primarily feed them by tearing pieces from a fish and passing them into the nest cup. At 2 weeks of age, the youngsters can already move around the nest and feathers are beginning to replace the down.
By the time they are one month old, the chicks have reached 70 to 80% of the adult size !!! – actively preening and exercising their wings. At 48 and 76 days of age they have developed feathers capable of flying (fledging). Gradually the wing-flapping increases until they are able to lift a little off the nest, finally taking their first, hesitant flight. For at least two weeks after fledging, the young stay close to the nest site, progressively improving their skills in the air during which time they return to their nest for food brought in by their parents. Soon after, they begin to make attempts to catch a fish for themselves. A young Osprey will only experience a 5% success rate – however, with practice, comes perfection . . .
Ospreys become sexually mature at approximately 3 years of age.