It looks likely that BB, Peter, Skinner, Waller and Whortle have failed to complete their migration this year, or their tags are no longer transmitting, and so we will be moving all of them to the inactive section of the website.
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
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.
We are concerned about whether we will receive further transmissions from Peter and Waller. They were in the same area and just 5km apart from each other, close to the Congo river in Democratic Republic of Congo, when signals were last received. Looking at the map, they seem to be in an area of unbroken canopy so the solar-powered tags may not be able to charge as they are not receiving light. The worry when batteries cannot charge over several months is that they may start to degrade and are not then able to switch on again when they do receive light. We will have to wait and see whether we receive further signals from the tags in future.
Since the 28 September Waller has been moving south, reaching Central African Republic by 29 September and continuing on to the Democratic Republic of Congo by the 1 October. He has travelled 1170km (725 miles) since 28 September and has now joined other Cuckoos in the Congo rainforest.
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