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Satellite Osprey Pete: Winter 2007–2008

Pete's wintering area:

Pete arrived at his wintering site on 23 October between 16 and 19 o'clock . The area by the Saloum river in Senegal lies 32 km from the Atlantic coast and 61 km north of the Gambian capital Banjul at the mouth of River Gambia . Judging from the determination of Pete's autumn migration, we can assume that Pete knows the area from previous years.

During the first month (23 Oct at 19 – 23 Nov at 17), all possible 231 fixes on Pete have been registered. In accordance with the settings, fixes were registered every three hours, eight times a day, until mid-November, but after that they have been registered only between 5 and 20 o'clock , i.e. six times a day.

During this month, 97 % of the fixes arrived from an area of 1.2 km2 within a labyrinth of sand dunes at the wide delta of Saloum. The part of the delta along the shoreline is the Delta du Saloum National Park. The satellite has caught Pete outside this core area only seven times. In all these cases, his fishing trips have taken him inland, at most 14 km from the centre of the core area. According to the fixes, Pete has not visited the Atlantic to fish there. Naturally, since the fixes are registered only every three hours, we do not know every single move Pete makes, so it is possible that he has flown to the shore, as well.

If we include all the fixes in our calculations, Pete's ‘home range' during the first wintering month was 29,5 km2 large. All night-time (at 18-6) fixes (107) have arrived from an area of only 35 hectares.

Pete stayed in his wintering area at the Saloum river for five months and one week, much longer than he spends at his nesting place in Finland each year. Pete’s satellite transmitter worked perfectly in the Senegal sun; all the pre-programmed positionings were read successfully! We received a total of 1,024 readings, of which 630 were logged during the day and 394 during the night (at 18-06).

Pete’s home range during the winter was about 658 km2, and the area covered by daytime positionings was the same size. However, all nighttime readings came from an area of only 0.63 km2. If we include 95 % of the daytime readings, the main daytime area will only cover 29.5 km2. Of the daytime readings, only 5 % were logged over 5 km, 2.4 % were logged over 20 km, and 1.3 % were logged over 40 km from the centre of his winter home range. According to the satellite’s observations, the furthest Pete went from the centre of his home range was 47.3 km (P1018).

At the beginning of his wintering period, Pete made a few 10-15-km visits inland to the east-northeast from his base (e.g. P434). It was not until early February (P656) that we had our first clear indication that Pete had to have found an exceptionally good fishing area at the upper courses of the northern tributary of River Gambia. It was obviously worth the 40-km-trip from the Saloum river. The satellite discovered Pete at the upper courses of River Gambia 12 times. One of these observations was made at 17 o’clock and the others at 13-14, which indicates that Pete made these long trips in the afternoon. In addition to the readings from River Gambia, a fair number of positionings were also logged from the route between rivers Saloum and Gambia. It is surprising that the satellite never observed Pete at the Atlantic shore or flying in that direction. The westernmost positioning (P686) was logged only 2.8 km from the centre of Pete’s home range.

Thanks to the flawlessly working transmitter and successful programming, we have gathered more detailed data than before on how Ospreys spend their winters.

Pete's spring 2008 »