Ospreys: How Bolton Castle is helping to keep the magnificent osprey alive

But now, as the first ospreys begin the long journey south to wintering quarters in Africa, one might turn up anywhere around lakes and reservoirs – recent sightings have included three at Gouthwaite reservoir, North Yorkshire, two at Eccup reservoir and three, including a young male ringed in Perthshire, at the St Aidan's reserve in Leeds.

It is a leisurely progression with none of the urgency of spring when they are on their way back to breeding sites and one might linger a week or more in an area where there is an ample supply of fish.

Young ospreys first take to the air during the first half of July but hang around the nest site until mid August when the family begins to split up.

The adult female leaves first for wintering grounds in West Africa to be followed by the oldest of the three or four chicks.

The younger chicks then depart and last to leave is the adult male who has lingered to ensure the chicks are able to catch fish themselves.

But the young ospreys, each migrating on their own, have a particularly hazardous time as some will still not have totally mastered the art of fishing.

It is estimated that only around 50 per cent of them survive longer than the first year. and other dangers they face on their journey via France, Spain and Morocco include easterly winds blowing them far out into the Bay of Biscay to be lost at sea.

After that there is the ordeal of crossing the Sahara where ospreys might go four to six days without food and the risk of death is the highest of anywhere on migration.

A small number of ospreys now winter in Spain and Portugal but the majority still continue on to the coastal marshes of West Africa where they will remain until they reach full maturity.

Some of them might do a practice migration aged about two and are seen back in the UK before they are ready to breed but most return to the country where they bred in their third summer, and then attempt to find a mate and nest site.