We have already learnt a lot from the satellite tracking data of Einion, Dulas, and Leri. What is becoming clear from this research and other studies in the UK is that young ospreys face huge challenges once they reach west Africa. It's not the 3,500 mile journey that seems to present the biggest danger, but surviving once they get there. There is increased predation pressure for sure, as well as competition for good fishing areas from older, established ospreys.

Having concentrated on Leri recently, we shouldn't forget her two brothers, of course. Dulas has been in the same area since September 29th, almost six weeks, on what looks like a marshy area just three miles north of the Gambia River, around 100 miles inland from the mouth of the great river.

Both Dulas and Einion seem to have found areas they are happy with. However, Dulas seems to be in habitat that could be prone to drying up over the winter months; will he start to move on if this area dries up? Looking at the map, he has already made a few trips to the Gambia River itself  - why does he not stay there? Is he coming up against other full adult ospreys that have established themselves here for many years and is sent packing?

Just like dinosaur bones can only tell you so much about the animal, they can't tell you what colour they were for example, satellite trackers for all their benefits cannot tell you exactly what is happening where the osprey is and what the bird is doing. Neither can they tell you about the condition of the osprey or how many predators and other ospreys there are in the area. We hope, of course, that six weeks in the same area is good news - plenty of fish, getting in good condition after the migration, and so on.

Roy Dennis and the BBC are on the Gambia River this week looking for Dulas and Einion - will they find them? Will they be strong healthy birds like we hope? We've not heard anything back yet so we honestly don't know. Roll on this Friday's Autumnwatch..