Friday, 21 January 2011

West Africa - Week 2

There is no doubt that if you spend four weeks in West Africa in January that you will see lots of Ospreys. I knew this before we flew to Banjul last week, but I really wasn’t expecting to see them in the numbers that we have done during the first ten days of the trip. By the end of the first week our tally numbered over one hundred individual birds, and we have added to that quite considerably after a few more days in the south of Gambia. This week we are returning to the various sites we visited during the first eight days of the trip, this time with a second group of project volunteers. It was sad to wave goodbye to the first group at Banjul airport on Tuesday afternoon, but great to welcome the second group a couple of hours later.

Aside from the sheer number of Ospreys, it has been a real privilege and extremely interesting to watch the birds’ behaviour on their wintering grounds. Something that has really surprised me, is that the adults birds are generally very tolerant of each other. The best example of this was at the Sine-Saloum Delta in Senegal last week when we saw 11 different Ospreys perched within a couple of hundred metres of each other. Thinking about it though, maybe I shouldn’t be surprised at all – remember, these birds will all know each other. Satellite tracking and other studies have shown that Ospreys return to the same wintering site every year; sometimes for more than twenty years. So if the same birds are returning to the same site each year, they must recognise each other. As long as there is plenty of fish, there is no need to waste energy chasing off a bird that you have seen every winter for the past ten or so years. Having said that, things are very different if an unknown juvenile appears. While one adult bird will let another pass directly over head without flinching, it is a totally different story if the bird flying over is a juvenile. In this case the adult bird will usually give a ‘chip’ call to warn off the juvenile, and if it doesn’t get the message, it will give chase. We have seen this behaviour over and over again in the past week and so there is clearly a hierarchy at all wintering sites. If you’re an established bird, then no problem. If, on the other hand, you are a juvenile who has arrived in West Africa for the first time then, good luck. This of course explains why the juvenile birds wander so widely during their first six months in Africa; they are looking for somewhere rich in food, but also where they will be accepted by the locals!

Another very interesting aspect of wintering behaviour that we have witnessed during the first ten days, is the differing ability of adult and juvenile birds to catch fish. In places where fish are abundant, such as the Sine-Saloum delta, and the coastline of Gambia south of Banjul, adult birds have very little difficulty when out hunting – most catch a meal within minutes. For juveniles though, it is a very different story. On Wednesday afternoon this week we visited Bajoli Island, situated about two miles off the Gambian coast at Tanji. This small sandy island is home to a huge colony of nesting Caspian Terns and Grey-headed Gulls and numerous wintering Ospreys. During a two hour visit we saw somewhere in the region of 10-15 different Ospreys, several of them juveniles. If the amount of fish brought back to Tanji every day by the local fishermen is anything to go by, the sea here is teeming with fish, thereby providing rich pickings for a hungry Osprey. You wouldn’t have known it though if you just watched the young Ospreys. Time after time, they hit the water but failed to come up with a fish. One particular bird must have crashed into the water on more than a dozen occasions before it finally came up with a fish. And by the time it eventually dragged a fish out of the water, it was so exhausted that it didn’t have the energy to eat it; instead it just flopped down onto the beach and sat there, exhausted. The sad reality is that this clearly demonstrates that surviving their first migration does not guarantee that a young Ospreys will survive to adulthood. It takes time for the birds to refine their fishing technique – and those that do not do this quick enough, probably don’t make it. A very clear example of natural selection in action.

Before our boat trip to Bijoli Island on Wednesday, we visited a primary school in Tanji, a fishing town of some 15,000 people a few kilometres south of Banjul. As I said in the blog last week, one of the main aims of our trip is to establish links with people in West Africa, and it seemed that a school was a good place to start. More than 1200 children aged 5-14 attend Tanji school. Significantly, all live within a couple of miles of a coast where numerous Ospreys catch fish every day during the winter. During our visit I gave a talk to 30 or so pupils about our work at Rutland Water in an effort to try and emphasise how special these birds really are. The kids all seemed genuinely interested. I’m not sure how many of them knew what an Osprey was before the visit, but they certainly do now! We now plan to link Tanji school with a primary school in Rutland to allow the children to write and keep in touch with each other, with Ospreys as the link cementing their relationship.

Among the numerous Ospreys we’ve seen since my last update, several have been colour ringed. Of these, we managed to read five of them. Four of the birds were German and one, French. It will be really interesting to find out a bit more about each bird and specifically to see how many winters they have spent in West Africa. I will of course report any news on the blog. Roy Dennis got back to me last week to say that the Scottish juvenile we saw at Sine-Saloum was ringed at a nest in central Scotland. I wonder if the neighbouring adult birds will allow it to make the mouth of the River Saloum its regular winter home?

Finally I must mention our guide, JJ. JJ has been leading bird tours in the Gambia and Senegal for many years, but I don’t think he’s ever lead two groups quite like us. Of course he knew about Ospreys before, but he certainly knows a lot more now! If you are planning a trip to the Gambia or Senegal then I would urge you to get in touch with JJ; he is extremely knowledgeable, enthusiastic and good fun to be with. He also now knows a fair bit about wintering Ospreys. Check out his website Your trip to the Gambia wouldn’t be complete without him.

I’ll post another blog next week, but in the meantime we’ll add some more photos over the next couple of days. Make sure you also watch out for some video diaries on the project’s youtube channel too.

Tim Mackrill