So it seems like Boris got lost in Mauritania.

Well, the evidence isn’t conclusive yet, but the outlook is bleak.

His last transmission was from almost a month ago, on August 21st, and he was still a few hundred kilometres short of crossing the Sahara, a desolate expanse of sand and gravel with very poor feeding prospects. Whilst Victor is currently safe in the rainforests of Central Africa and Mr Conkers seems well ensconced in a fertile part of Senegal, the lack of signal from Boris is concerning.

Whilst all this might sound like a CIA report about communications with their field operatives, it is in fact the latest news on three cuckoos who have left the fair shores of England to travel south in order to avoid the Northern Hemisphere winter.

The common cuckoo. These birds are incredibly similar to the African cuckoo, but have slightly less yellow at the base of the bill. The lower mandible also has a slight yellow-green tinge to it. Photograph by Alex Jordan.

With the number of cuckoos in the U.K. having declined by roughly 50% in the last 20 years, the British Trust for Ornithology (BTO) has established a cuckoo-monitoring program, tracking the birds via satellite, to try and understand why. Seeing where the birds go on their migrations, analysing their routes and behaviour patterns, should hopefully provide a base of knowledge that may assist in conservation efforts. A number of birds are currently named and are being followed, and you are even able to sponsor a bird, the donations form which go towards funding the tracking monitors.

The technology that allows these birds to be satellite tracked is what blows my mind. Given that as recently as the 19th century, European ornithologists still had no idea where some of the birds went in winter, the fact that scientists are now able to plot an individual bird’s course over thousands of kilometres is nothing short of incredible! Obviously any transmitter needs to be as non-invasive – and therefore as small – as possible, so as not to hinder the birds’ natural movements. The trackers currently used are a brand new design that are charged by tiny solar panels also fitted to the bird. Although a few teething problems have been found with these new trackers (apparently the cuckoos’ feathers can partially cover the solar panels, resulting in weak signals, or none at all), a number of the birds have been transmitting regularly, and the accuracy with which one can follow the bird’s daily movements is astonishing.

The biggest natural barriers to the cuckoos as they fly south to Africa are first the Mediterranean Sea and then the Sahara desert immediately afterwards. If one looks at the birds’ movements before attempting this huge leg of the trip, one constant between the individuals seems to be a refuelling stop in southern Europe before launching into what must surely be the most hazardous part of their journey. It would appear that the birds are stocking up on food, maximising their energy reserves for the Saharan leg (some do break their journey briefly just as they reach North Africa) before flying across in one all-out, non-stop effort.

As we speak, thousands upon thousands of cuckoos are heading south through Africa. Photograph by Mathias Putze.

The current front-runner of the cuckoos being monitored is Victor, whose latest transmission places him in the northern corner of Gabon, after having routed from Spain to Algeria, winging it across the Sahara literally overnight (a distance of approximately 2000km in one go!), then moving down through Burkina Faso and Nigeria to his current position where he seems to be staying for the time being.

Victor’s route from the UK to his current location in Gabon.

Victor’s Daily movements in the Gabon rainforest, just south of the border with Cameroon. His daily movements are rarely more than a kilometre.

It is not only the common cuckoo that is moving south through Africa at this time of year. Eleven different species are encountered at Londolozi, all of whom are migratory (although one or two individuals do over-winter on occasion). The distinctive call of the Klaas’ cuckoo is already being heard, and it won’t be long before the rest follow. The caterpillars that form the majority of most cuckoo’s diets here are about to emerge with the bloom of summer, and it is this food source that the birds are going to be arriving to take advantage of.

So far none of the cuckoos tagged in the BTO project have made it down to South Africa, or even Southern Africa. The majority of the European cuckoos (now called the common cuckoo) I think tend to spend the African summer slightly further north of us, and they are relatively uncommon visitors to Londolozi, with the African cuckoo (visually almost exactly the same) being seen far more regularly in this area.

I am hopeful though, that one day I might be looking through my binoculars at a cuckoo and see a tiny transmitter attached to it, and know that Victor has made it all the way from the U.K. to Londolozi. Or at least I’ll pretend that it’s him.

Then he’ll just have to make it all the way back again!