Over the past two decades satellite tracking has provided a unique insight into the wintering behaviour of ospreys. Whereas juveniles usually wander over a large area after arriving in West Africa, adults head straight to a known wintering site. Many of the adult birds we have tracked have been remarkably sedentary in winter; often occupying a home range of 1-2 km². There are always exceptions to this rule, however, and it has been fascinating to follow the daily movements of Jules since he arrived at his winter home in the Casamance region of southern Senegal. Jules is living in a larger area than most adult ospreys, but mainly because his regular roost site is 16 km from his favoured daytime perching and fishing sites.
Jules has spent each night roosting in an area of dense mangroves, and has four favoured perches within an area of just 0.04 km².
Jules roosts in an area of dense mangroves each night.
In this part of the Casamance delta he is surrounded by potential foraging grounds, including a section of river that is almost 1 km wide, just 2 km to the south. However the satellite data indicates he does little or no fishing in this area, and instead flies 16 km WSW to spend each day on the coast. There he favours a 1.3 km stretch of sandy beach and hunts just offshore. The satellite data indicates he probably catches most of his fish around 200 m out to sea, but on occasion he flies further out, such as 1.1 km on 3rd December and 2.65 km on 19th November. Most of these fishing trips tend to be late morning or early afternoon, and he then eats his catch on the beach.
Jules spends most days perched on a sandy beach, and fishing just offshore.
The map below gives an indication of just how predictable his daily routine is. The red circle, centered on his roost sites, indicates an area with 50 % of GPS fixes while the orange area shows the location of 95 % of fixes. In other words, when he is not at his roost site he is nearly always at the coast. Interestingly he has flown east from his roost site on just two occasions in the past month.
Over the past month Jules has roosted in the mangroves each night and then flown 16 km WSW to spend the day on the coast. The red circle indicates an area with 50% of GPS fixes and orange shading 95% of GPS fixes (calculated using kernel method).
Jules’ winter home in Senegal is 30 km south of The Gambia and 20 km north of the Casamance River.
Don’t forget that Jules’ latest winter movements as well as his migration from Scotland are shown on our interactive map.
