Updates from our Cuckoos

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

Two of our tagged Cuckoos are already moving west and are well on their way back to their breeding grounds in the UK!

Hennah had moved 2500km (1500 miles) to Ivory Coast by 8 February from a position on the northern forest edge on 6 February, low quality signals tell us, but by the 9 he had already continued west a further 820km (510 miles). He is now just inside the border of Sierra Leone in an area where the Lofa-Mano National Park and Gola North Forest Reserve meet, where presumably he will rest for a while after such a long journey in such a short amount of time. 

Meanwhile, Ash was in Nigeria on the 8 February but by the 9 he was in Ghana, north of Lake Ghana and the Digya National Park. 

Although this is not especially early for them to move into the region - in previous years we have seen the first cuckoos move to West Africa by mid-February - Hennah's stopover location especially is very far west for the date, as early stopovers tend to be further east. It is notable that both stopovers are within the humid forest zone, rather than to its north as most West African stopovers are - this could compensate for the birds being so far west at this time, before the savannahs in the area have been rained upon. 

David has left Lake Mai and travelled 380km (235 miles) north to an area close to the Congo River and just above the equator. 

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.

Livingstone has disappeared off the map but we received low quality signals from his tag on 31 January just a few days ago. Hopefully further signals soon will confirm whether he remains in the area or has been feeding up in preparation for a bigger movement. 

It looks like a few of our Cuckoos are setting off on their first spring migration movements. Ash and Emsworthy have both joined Stanley in making a move northwards to the Congo rainforest edge while Derek has been in the area for a few days but only transmitting low quality signals, until now, which hadn't registered on the maps. 

Several of our Cuckoo tags have not sent transmissions for over 10 days; BB, Hennah, Peter, Skinner and Waller. 

This means they are not currently shown on the main map by default, although can be switched on using the tick boxes under their photos. It's not uncommon for Cuckoos to disappear for up to several months during mid-winter as tag charging conditions in the forest are poor so we won't really know their fate unless we receive further transmissions. If they fail to move northwards when expected then either the Cuckoo may have died or the tag may failed or degraded. Our greatest concerns are still for Peter and Waller who were in the same area when signals were last received, all the way back in October.

No signals had been received from Chris' tag since the 21 Janaury but by the 2 February Chris was on the move again. Low quality signals show he had travelled the 490km (300 miles) north it took to leave Angola and take up a location in the  Reserve de chasse de la Lefin in Congo. This is the first stage of his migration north as he moves into the area many of the other tagged Cuckoos spent the winter. This isn't currently on the map due to the low quality but hopefully further signals will be received shortly confirming his location. 

Stanley has made a huge movement of 740km ( 460 miles) and travelled to the northern edge of the Congo rainforest. This is the first step of his migration home and he is now around 250km (150 miles) further north than the nearest Cuckoo, Derek, and 1350km (845 miles) further north than the most southerly of our Cuckoos, Chris.  Our Cuckoos seem to move to the forest edge to feed up for a while before then heading into west africa. 

In previous years David has also made his move as early as the end of January to the forest edge while BB and Chris have moved in February and early March.  

On the 23 January we received transmissions from David's tag showing he had moved 200km (125 miles) north to Lake Mai, an area recently vacated by Emsworthy, who has travelled further north.