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How ornithologists keep track of Suffolk cuckoo PJ on his travels across the world




He is one of the world’s most frequent fliers but despite the Covid pandemic PJ has carried on clocking up air miles untroubled by red lists, quarantine or travel restrictions.

Two weeks ago he was in the Pyrenees having left the UK in mid-July. He stopped over in France before taking off again for Spain.

His final destination is the tropical rainforests of Africa where he will stay until next spring before setting off on the return trip.

Satellite tagged Cuckoo by Neil Calbrade
Satellite tagged Cuckoo by Neil Calbrade

No tickets, vaccinations or passport required... because unlike human flyers this traveller is relying on his own wings to carry him on what can be a perilous journey.

Early yesterday morning he was well into the hardest stage and was flying over the central Sahara. Rare rainfall in the mountains may have allowed a welcome break and possibly the chance of food but he is not out of the woods yet.

PJ is a cuckoo. In the six years since he hatched in a Suffolk forest he has already flown more than 90,000 kilometres.

PJ the Cuckoo by Phil Atkinson
PJ the Cuckoo by Phil Atkinson

And since 2016 ornithologists have tracked him every flap of the way on his annual journeys between the woodland where he was born and Africa’s Congo Basin.

On his back PJ wears a satellite tracker that allows scientists at the British Trust for Ornithology (BTO) to constantly monitor his position.

He is one of more than 90 cuckoos fitted with the devices since the project began 10 years ago in a bid to find out why the number of birds visiting the UK had nosedived.

Sadly it has shown that many do not survive the gruelling migration - a round trip of about 15,000 km which includes flying over the Sahara Desert.

Cuckoo. Picture: Edmund Fellowes
Cuckoo. Picture: Edmund Fellowes

Cuckoos arrive in Britain in April and their distinctive, evocative call used to be a common sound in the countryside.

Once here they mate and produce eggs, but dodge the task of childcare by laying their eggs in the nests of other, smaller birds like reed warblers, meadow pipits, and dunnocks.

The tiny hosts work tirelessly to feed the chick which soon pushes any other eggs or fledglings out of the nest.

Meanwhile the adult cuckoos strive to fatten up for the return trip to Africa on a diet of insects, with large hairy caterpillars - toxic to other birds - a particular favourite.

“They have stolen a march on other birds in that way, as with nesting,” says Dr Chris Hewson, of the BTO.

Dr Chris Hewson - picture by Mike Toms
Dr Chris Hewson - picture by Mike Toms

Chris, who leads the tracking project, said in the UK farmland, wetland and migratory birds are declining much more quickly than other species.

“The core of our work has been volunteer-led undertakings, to get very precise information about bird distribution and population.

“More recently we have started to do more research trying to work out what is going on with some of the declines and how those populations could be put back.”

There were three main reasons the cuckoo was chosen. First, it was declining heavily across the whole of the UK. Second, it is big enough to cope with the weight of a tracking device. “The cuckoo is quite large by the standards of migratory birds so we could use satellite tracking on them,” said Chris.

“The main advantage is you can get live information. You don’t have to catch the bird when it comes back to see where it has been.

“The third reason is we thought cuckoos from the UK went south east to Italy when they started their autumn migration, but didn’t know much about where they went after."

The progress of 12 cuckoos currently being tracked can be followed by enthusiasts on the BTO’s website. The data provides vital information including where the birds might perish on route.

“The number we track varies between the years depending on how many birds are still going from previous years. The tracking packs are expensive - £4,000 each.

“We tagged five in the first year, in the Norfolk Broads and Thetford Forest, because they are near our base in Thetford, and are where the populations were declining most.

“Three of the birds went where we thought, but two went through Spain. We were quite excited by that, and were also surprised by how early they migrate.

“They mate, lay eggs, then they can disappear. By the beginning of June some are already starting to go.”

This year everything has been later because of the cold spell in spring, but even so one bird had reached the south coast of France by the end of June.

Whichever route they take, they all head for the same part of west Africa, then carry on south and winter in the Congo basin, just south of the equator.

The call of the cuckoo - which also breeds as far away as eastern Russia - might seem as British as a buttercup meadow, but Africa is their real home.

“They are rainforest birds,” said Chris, who has worked for the BTO for almost 20 years.

“The reason they spend summer here is to exploit the resources, but the cold doesn’t suit them in the winter.

“They are now tagged from all across the UK, and from upland and lowland habitats. Birds going via Italy survive much better than those going through Spain.”

But in the path of all the migrating cuckoos is one of the most inhospitable places on earth ... the Sahara Desert.

A thousand miles of blistering hot sand lies between them and the relative safety of the other side,

“It takes them about two and a half days to cross the Sahara,” said Chris. “Sometimes none of our tagged birds has successfully crossed the Sahara after leaving Spain.

“They fly very high when crossing the desert - three miles above the surface - to try and keep cool.”

The satellite tags are made by US-based Microwave Telemetry, and weigh only five grams. But to tag a cuckoo you have to catch it first - and although the technology is sophisticated, the method is not.

“We use a stuffed female cuckoo on a stick, and a recording of their mating call, put it in an isolated bush and surround it with nets,” said Chris. “The males get very excited and fly into the net.

“Fitting the tag is quite a painstaking procedure It is fixed by a harness pretty much like a rucksack. You fit it below the feathers, loose enough that it is not constrained, and tight enough so it isn’t moving around the bird.”

The solar powered tags emit a constant radio signal. “Ninety-odd birds have been tagged so far,” he said. PJ has been tagged for five years. But they only have a 50 per cent chance of surviving from one year to the next.

“They all have names given to them by people who are sponsoring birds. People pay us £4,000 for the privilege of naming the bird.”

PJ was caught and tagged in the King’s Forest north of Bury and is named in memory of Pamela Joy Miller who passed on her passion for bird watching to her family.

He comes back to the forest every year. “Basically they will return to the area where they were born,” said Chris.

“We’ve recorded him flying 75,000km so far, so with his first year (when he wasn’t tracked) he will have done 90,000km. He is really unusual in that he has used both the eastern and western migration route.”

With every cuckoo named - Clive, Calypso and Harry are among those currently heading back to the rainforest - the project team cannot fail to become fond of them.

“Once you put a tag on a bird you feel a sense of responsibility for how well that bird does,” says Chris.

“Generally it’s been quite surprising how much people do get attached to them.”

To follow the cuckoos go to bto.org and click on Our Science, then projects.

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