Updates from our Cuckoos

On 5 March we received one good signal from Fred's tag which showed that he had moved to the northern forest edge, where many of our tagged Cuckoos have moved to before heading to West Africa.  

From time to time we ‘lose’ one or two of our Cuckoos only for them to reappear several days, or even weeks, later. We are never entirely sure why this might be at the individual level but during the course of the project we have noticed similarities between some of the ‘lost’ birds.

We have lost some of our birds just prior to them making a large movement and we think that this might be because they move into denser vegetation in order to feed up before embarking on a long flight. Moving into denser vegetation may mean that the solar panel that recharges the battery for the tag is in shade for periods of time and the battery receives a poorer charge, which in turn results in poorer performance from the satellite tag.

Once the birds have put on enough weight to begin their journey they move into the open and the tag begins charging again and the birds ‘reappear’. We also see the same thing happen, although to a lesser extent, when birds complete a long movement and presumably move into denser vegetation to rest and feed up

There have been a few small movements recently. Fred and Jake have moved west into Congo whilst David has moved into the area that Emsworthy has left. 

These are likely down to changing rainfall conditions which may affect food availability and cause the Cuckoos to seek areas which may be more plentiful in resources. It will be especially important to find a good feeding area before they make any move northwards. There's no consistent direction in which these Cuckoos leave an area and one Cuckoo may move from an area only to be replaced by another moving in from elsewhere, with no obvious reason why.

Fred and Jake, two of our Cuckoos tagged in Sherwood Forest, have moved westwards and are now in Congo. Fred recently left the Mbandaka area and has moved about 270km (165 miles) west from his previous location in Democratic Republic of Congo, while Jake, who is about 70km (45 miles) further south, travelled a shorter distance of 155km (95 miles). 

Interestingly, Derek who is slightly further north, had been moving east, the opposite direction to Jake and Fred, until recently but he has backtracked around 65km (40 miles). Emsworthy has also moved, but northwards to the area not long vacated by Fred. These movements may indicate changing conditions which are encouraging the Cuckoos to seek more favourable areas. 

From his position in Congo, Fred had moved east and into Democratic Republic of Congo by Christmas Eve and was close to the River Congo. He remained in the area until 12 January before then moving 145km (90 miles) west, crossing back into Congo but remaining in the area of swamp forest. 

Fred is in Congo, close to the border with Democratic Republic of Congo and 88km (54 miles) north west of Lake Tumba. We last heard from him at 09.06 on 17 December.

Yesterday evening and early this morning we received signals from Fred's tag showing that he was on the move and was finally travelling south towards the Congo rainforest. The last location received shows he stopped in Cameroon, having travelled 1030km (640 miles).

Both Sherwood birds 134957 and 134955 have moved over 700km (470 miles) east from their locations in Burkina Faso in the last few days and are now in northern Nigeria. This leaves just Chester in Burkina Faso who becomes our most westerly bird by over 960km (595 miles). 

With most cuckoos now in the Sahel region, we're entering a fairly quiet period in the annual cycle of the tagged cuckoos with less movement than during the migration season.

Birds who completed their desert crossing will spend time in the Sahel recovering their body condition, and some may stay quite a long time. In previous years, cuckoos have stayed in this area for as much as several months, while others spend a shorter amount of time before moving south into the humid zone forests.

The eastern Sahel in Chad and south Sudan has received plenty of rain recently, and thus conditions are likely good for cuckoos. Northern Cameroon was slightly drier than average in August, and so cuckoos such as Derek, Dudley, Stanley, and Emsworthy may be moving on if foraging conditions aren't suitable.

Cuckoo 134955 has moved east from Mali and is now in Burkina Faso. He has been joined by Chester, who moved on quickly from his location in Mauritania. They are further west than many of the Cuckoos and, by taking the western route through Spain, have a longer journey to get to the Congo Rainforest than some of other Cuckoos but they will have been able to cross the desert at one of its narrowest points.