Most European Ospreys nest in the north and winter in Africa south of the Sahara (apart from a few Mediterranean populations which are more or less sedentary). A few birds stop before crossing the Mediterranean and winter in Spain or even in the south-west of France, but this is unusual. In Switzerland Osprey migration occurs over a fairly wide period, and small numbers of birds can be seen mainly from mid-March to the end of May in the spring and from mid-August to the end of October in the autumn.
Unlike most other raptors, the Osprey is such a strong flier that it can migrate over large stretches of water and doesn’t have to follow continental edges or cross over straits in order to find updrafts. They can therefore migrate as they like, even if they do tend to avoid flying over high mountains in Europe and often follow the West African coast. Remarkably they can cross the Sahara in one single go, which means flying solidly for some 40-66 hours.
Mortality of young birds is very high; about 40% of them don’t survive their first year and only about a third live to adulthood. However, survival rate of the adults is much better with mortality estimated at about 10 % per year.
Ospreys, even young ones, migrate all by themselves and do not need their parents to show them where to go. They instinctively know the way, even if often they do not follow the most direct path (it has been shown that their migration routes improve with practice). The young birds usually leave in the same order that they were born, at one or two day intervals.
After their first migration south, most European Ospreys spend their second year in Africa. Some rare individuals might fly back to the north at the early age of one year (although more often at the age of two), as a sort of as a “test drive”. However, at that age they do not return to breed and do not necessarily even fly as far as to the place where they were born.
For a number of years some birds have been fitted with satellite transmitters in order to follow their migration from Scotland, Sweden, France, Finland, England and the USA which has revealed a few of their secrets. It is even possible to follow these Ospreys « live » (here is a great map showing the paths of some Ospreys from both Europe and North America). Note that the Finnish birds tend to (but don’t always) winter in eastern Africa, whereas the Scottish and English birds go towards western Africa. Another interesting point is that Ospreys are often as loyal to their wintering areas as they are to their nesting areas. Once they have chosen where to spend the winter they tend to return to the same place each year.
In December 2014 we were lucky to be able to observe « Green J », a 23 year old female that Roy Dennis fitted with a satellite transmitter and who has been followed since 1999. Unlike most Ospreys which spend the winter in Africa, Madame spends her winters all by herself in an enormous reservoir in Extremadura in Spain. Our observation of “Green J” was recorded in her blog.