In 2001 two papers were published in the Journal of Avian Biology 32: Copenhagen 2001 reporting on work carried out at the Grimso Wildlife Research Station, Dept. of Conservation Biology, Riddarhyttan Sweden and the Dept. of Animal Ecology, Lund, Sweden. Satellite tracking of Ospreys on migration had been carried out there between 1995 and 1998. Below is a summary of some of the key findings reported in the two papers.
Satellite tracking of Swedish Ospreys Pandion haliaetus: autumn migration routes and orientation
by Mikael Hake, Nils Kjellen and Thomas Alerstam. J. Avian Biol 32: 47-56.and
Timing and speed of migration in male, female and juvenile Ospreys Pandion haliaetus between Sweden and Africa as revealed by field observations, radar and satellite tracking
by Nils Kjellen, Mikael Hake and Thomas Alerstam. J. Avian Biol 32:57-67.
In the period 1995-1998, 18 Ospreys from the area around Grimso in south central Sweden were satellite tracked in order to determine their autumn migration routes. Of these, 13 were followed during the entire migration (6 females, 5 males and 2 juveniles).
Most of these birds migrated across western and central Europe to winter in tropical West Africa. 8 birds flew through the Iberian peninsula into Morocco; 4 crossed the Mediterranean further east, using Sicily/Malta or Corsica/Sardinia, and one female used an extreme easterly route avoiding the Mediterranean altogether by flying first to Kazakstan and then through the Caucasus and the Red Sea. None of these Swedish Ospreys were recorded passing through the UK. (But some do - see Update for 18/2/2001)
Wintering sites recorded were: 2 in the Ivory Coast, 2 in the Gambia, 1 in W Senegal, 1 in S Senegal, 2 in Guinea Bisssau, 1 in Mali, 1 in Sierra Leone and 1 in Central Guinea. However, one juvenile flew to Cameroon and the female using the easterly route eventually reached Mozambique. On average, the birds travelled a total distance of about 6700 km, with little variation except for the female wintering in Mozambique, who travelled more than10000 km. They spent on average 45 days travelling, averaging 257km per day.
Of the six juveniles tracked, only two reached Africa. One may have collided with power lines and contact was lost with the other three after extended stop-over periods. One adult male and one adult female are also assumed to have died during migration.
21 stopovers of duration from 1 to 44 days were recorded, of which most were in northern or central Europe and only five south of 45°N, three of these being in Africa. Females departed before males and juveniles and flew to a stopover site with which they probably were familiar. After 3-4 weeks there they continued to their wintering grounds. Males and juveniles also usually made one or more stopovers. Adults seemed to travel to a known wintering site, where they remained stationary, whereas juveniles were more mobile after reaching tropical regions. Adult Ospreys followed very straight migratory routes with overall mean directions of 185 to 209 degrees, whereas juveniles tended to be more variable in orientation.. The Ospreys did not avoid geographical obstacles such as mountain ranges and deserts but did seem reluctant to cross large water bodies. Migratory activity usually took place between 8:00 and 17:00 and there was no indication of movement at night.
13 of the Ospreys were fitted with transmitters powered by conventional batteries and 5 with solar-powered transmitters. The battery-powered transmitters were programmed to transmit for 10 hours every third day to cover the autumn migration and part of the wintering period.
The two papers give much fuller details of the Swedish work and the first one includes three summary maps showing migration routes of adult males, females and juveniles.