Osprey Facts

 

Appearance

Male:

147-166cm wingspan, 56-60cm in length, 1400g in weight. Dark brown upperparts and cream underparts. Distinctive dark ‘highwayman’s mask’ around the eyes.

Female:

154-170cm wingspan, 57-62 cm in length 1600g in weight. Looks similar to male but often has heavily marked breastband.

Juveniles:

Similar to adults but lighter brown with pale edges to feathers. Full adult plumage develops by the age of eighteen months.

Food

Almost exclusively live fish. Ospreys look for fish by hovering over the water, although sometimes they are able to use a perch from which to sight their prey. They dive into the water with wings swept back, thrusting their talons forward at the last minute to grab the fish from below the surface. Adults are successful about once every four dives, but it takes juveniles many more attempts before they are successful. Ospreys hunt for fish in both salt and fresh water.
At Rutland Water the typical prey species are Trout and Roach but Ospreys will catch and eat any type of fresh or saltwater fish.

Breeding

Age at first breeding: 3-5 years
Number of eggs: Usually 3
Size of eggs (mm): 62 x 46
Incubation period: 35-42 days
Fledging period: 53 days

Life Cycle

Chicks

A young Osprey spends the first seven or eight weeks of it’s life confined within the nest (or eyrie); a huge pile of sticks lined with moss, bark and grass. It will be fed primarily by the female, who tears pieces from a fish and passes them into the nest cup.
At two weeks old the youngsters can move around the nest and after a month they are very active preening and exercising their wings. Gradually the wing-flapping increases until they are able to lift a little off the nest, called ‘helicoptering’ and then take their hesitant first flight.

Juveniles

For at least two weeks after fledging, the young Ospreys return to their nest for food brought in by their parents. Usually the young stay in the area, close to the nest site, as they improve their skill in the air, before they then begin to make attempts to catch a fish for themselves.

First migration

By late August or early September, the young Ospreys leave their nest sites and head south on their first migration. The young Ospreys fly alone, often without catching a fish for themselves before starting their journey. The majority of Rutland Ospreys winter in West Africa, although some are known to have spent winters in Southern Iberia. Young Ospreys will normally not return to the UK until they are at least two years old, some will not return for several years.

Returning to breed

Experienced adult birds leave West Africa and head north to their breeding areas again in March. However, younger birds may not reappear at the sites from which they fledge for several years. Some Ospreys will return when they are 2 years old, but do not usually begin to breed until they are 3 to 5 years old. Often a pair will build a nest and establish a territory in their first year together and will return to breed the following year.
Ospreys, especially the males, usually return to breed in the area in which they fledged. This explains the relatively slow expansion of range in Scotland. So the translocation of the young birds before they fledged was key to this project’s success.
Osprey pairs generally mate for life. Experienced, older birds usually arrive back in the nesting area first. Established pairs nearly always return to their previous nest sites. As new pairs establish, they must find new sites when they arrive after migration. It is also often difficult to find a suitable natural site to hold the nest. Nests are often over a metre wide and usually within 3-5 kilometres of water, preferred sites often have an open area around the nest, for easy access when landing. Flat-topped trees are the most likely natural sites, but Ospreys take readily to man-made structures, such as pylons, as well as artificial nests like those at Rutland Water.

Eggs and incubation

Female Ospreys begin to lay their eggs in late April. The eggs are beautifully blotched reddish-brown and are about the same size as a large hens’ egg. They are produced at two-day intervals: Novice breeders will usually lay two eggs; experienced pairs lay three or very occasionally four.

Both adults will take part in the long incubation process. The female takes the major role and the male provides her with food and defends the nest from any potential predators.
Until the chicks fledge, the female stays on or close to the nest site. After the young have fledged she joins the male in bringing food back to the nest site. Ultimately the young become independent hunters and the adults’ role as parent and provider is complete.

Life span

Due to the success of ringing programmes and the swift growth of digital technologies, making nature more accessible, we now know Ospreys can live beyond 25 years. In the spring of 2000, an Osprey with ring number M9976 was found electrocuted near Agadir, Morocco. It had been ringed as a chick in Scotland in July 1974. Loch of the Lowes female ‘Lady’ is currently thought to be the oldest breeding Osprey in the UK and has returned to the Scottish site for 22 years now. The oldest Osprey at Rutland Water is 03(97). He is 17 years old in 2014.