The Osprey is one of biggest bird of prey in Sweden. Only White-tailed Eagle, Golden
Eagle, Red Kite are bigger. It is breading in the whole of Sweden except for the island of
Gotland.
The Osprey is completely specialized for fishing. It catches other preys only in
exceptional cases.
As by all birds of prey the female Osprey is bigger than the male bird. The female weights
around 1,8 kilograms and the male around 1,4 kilos. The reason for this difference is not
completely clear but might be explained by the fact that the female generates the eggs and
therefore needs a lot of energy while the male is smaller to be able to hunt more
efficiently.
The work at the nest is strictly shared. The male is doing all the hunting for food and are responsible for building the nest. The female is producing the eggs and are responsible for feeding the young birds. The female are leaving the nest when the young birds have been ready to fly for 2-3 weeks. The male is left to feed them.
The female and the male are arriving to the breeding place nearly at the same time
during the first half of April. If one couple have been breeding together for one year they
are likely to return to the same nest the following year to breed again. The nest is built
in the top of a mighty pine tree.
Already after two weeks - mostly around the 25:th of April - the female is laying three
eggs with 2 days in between. Then the brooding begins. After about 35 days, around the end
of May / beginning of June the eggs are hatched.
At the end of July it's time for the first flight that is preceded by an intense training.
During 1-2 weeks the young birds are fluttering their wings in the nest, sometimes lifting
up to one meter above the nest. The young birds remains near by the nest for 4-7 weeks
while eating the fish that the male is catching. During this time they are developing their
skills of flying and are learning how to catch fish by themselves. As the female has left
the nest and the male is rarely present it's up to the young birds themselves to learn how
to hunt.
Swedish Ospreys are migratory birds. Most of them are spending the winter in western
Africa. The young birds are migrating without any help from the parents. In the end of
August or in the beginning of September they are leaving the nest heading south.
There are about 30.000 pairs of Ospreys spread around the world mostly on the northern
hemisphere. In Sweden there are about 3.000 pairs, which is nearly half of the 8.000 pairs
in Europe.
The number of Ospreys has declined during the last decades. Scientists know very little
about the reasons for this but as the Osprey is eating nearly only fish one reason is
believed to be the acidification of rivers and lakes that is decreasing the number of fish.
Also lack of rain and drainage of lakes in the areas where Ospreys spend the winter might
be an explanation. Illegal hunting and environmental pollution might locally be a big
threat to the survival of the Osprey.
The Osprey is relatively fearless during the breeding season as long as the disturbance is limited in time. It's the most sensitive just after hatching with is in the beginning of June. During the tours we will try to minimize the impact on the birds.
Source: Dr. Mikael Hake A.E. at Grimsö Research station
You can find some more information about the Osprey at The university of Minnesota.