Tracking the cuckoo’s arduous African journey, to the Congo and back

From the top of Prince William’s Seat, which straddles the Wicklow and Dublin Mountains, the dark green belt of native trees that extends the length of the Glencree Valley stands out from the surrounding patchwork of fields and mountain peat.

On a Sunday last April, as I descended the hill after an early morning run, I stopped on a wide granite outcrop halfway down and heard a clear, singular sound from inside the wooded greenway below. It was the call of a male bird, one who had just arrived from Africa, repetitively and rhythmically proclaiming his name to nearby females: cuck-oo! cuck-oo!

This call will soon be heard again in the valley because the cuckoos are on their way: a few weeks ago they left their wintering grounds in Africa’s largest tropical rainforest reserve, deep in the Salonga National Park in the Democratic Republic of the Congo, and embarked on their mammoth migration to breeding sites across Ireland.

Last May, researchers attached miniature solar-powered tracking devices to three male cuckoos, and their movements are being logged online as part of a joint effort between the National Parks & Wildlife Service (NPWS) and the British Trust for Ornithology.

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Sam Bayley, a wildlife ranger leading the project for the NPWS, says we know “little to nothing” about cuckoos in Ireland. What migratory route are they taking? Why has Ireland’s population decreased so much in the past two decades? How many return to breed here from Africa? And while they’re here, what are they doing – and where are they going?

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The three birds, called KP, Cuach Torc and Cuach Cores, were tagged in Incheens, Killarney National Park. When adult cuckoos leave Ireland in the summer, the biggest challenge they face during their journey to Africa is the epic crossing of the ever-expanding Sahara Desert, which they do in one go. To prepare for this journey, cuckoos often spend a few weeks in the Mediterranean to eat as much food as possible to build up their strength.

Last year, KP and Torc had a successful and straightforward migration to the Congo. They left Ireland in June and within a few days had crossed the Alps and reached northern Italy, where they spent time feeding. Crossing southeast to Montenegro and Greece before flying south across the Sahara, they arrived in the Congo Basin in September and October.

Females of many bird species sing complex songs, and understanding them will also help conservation efforts

Cuach Cores’s journey could have been smoother. Last June he left Ireland and landed in Italy, but instead of continuing southwards to Africa, he flew in the opposite direction towards northwest France. Researchers following his movements needed to figure out what he was doing – they wondered whether he couldn’t find enough food in Italy and instead looked elsewhere. But then, to their relief, after eight weeks in France, Cores took to the air and crossed the Sahara without landing, arriving in the Congo a few days later.

The call of the male cuckoo is familiar and famous, but the female’s call is equally distinct. It’s a bubbling call, often described as “bathwater gurgling down a plughole”, which she makes before she lays her eggs – up to 20 in a season – in the nests of other bird species. In Ireland, the meadow pipit commonly will be fooled into rearing the young cuckoo after it hatches.

Birdsong has historically been viewed as a distinctly male trait, with female songs understudied and overlooked. This has led to an unconscious bias in ornithology and a gaping hole in knowledge, especially given that half of all birds are females. Females of many bird species sing complex songs, and understanding them will also help conservation efforts. Scientists are quickly trying to catch up, leading to efforts such as the annual Female Bird Day in May and the Female Bird Song project, which encourage bird enthusiasts to identify and collect data.

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If you hear a female cuckoo singing but can’t identify it, download the free Merlin bird ID app; it will tell you within seconds the bird species singing. I recently began using it, and it’s revealed a whole world of birdlife for amateurs like me. It’s easy to use if you’re on a walk outside. Just open the app and press the large SoundID button, and it will record what it hears. It transforms the waveform into a spectrogram graph and uses a picture of the bird’s sound to make an identification.

Each bird species the app identifies lights up as it sings, which is helpful if you want to learn to identify birdsong by ear, or if you are hard of hearing. I’d particularly encourage farmers to use it as a way to understand which species are using their land.

Merlin was developed a few years ago by researchers in the Cornell Lab of Ornithology . They harnessed the power of artificial intelligence, machine learning and a global network of volunteers who have submitted recordings to their database of 1,218 species worldwide. Alli Smith, the project manager, says they’ve 15 million users, of which 82,000 are in Ireland (it’s particularly popular with people in Dublin, Cork, Galway and Kerry). Last year almost a million birds were identified here by the app.

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As we head into spring and our early mornings and late evenings are filled with birdsong, I cannot recommend the Merlin app enough. If you’re lucky enough to live near cuckoos, you might even begin to identify the female and her tropical, frog-like call.

To track KP, Cuach Cores and Cuach Torc, go to www.bto.org/cuckoos. For more on the Merlin app, see https://merlin.allaboutbirds.org/download.

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