Can cuckoos from Suffolk help discover why numbers of the bird are in sharp decline?

Cuckoo - Cuculus canorus PICTURE: BTO/Chris Knights

Cuckoo - Cuculus canorus PICTURE: BTO/Chris Knights - Credit: CHRIS KNIGHTS/British Trust for Ornithology

Cuckoos based in Suffolk are starring in the latest phase of an on-going study to find out why these fabled birds of the British countryside are disappearing at an alarming rate.

Chris Hewson setting nets at dawn PICTURE: BTO

Chris Hewson setting nets at dawn PICTURE: BTO - Credit: Archant

A total of five male cuckoos, caught in the county by specialists working for the British Trust for Ornithology (BTO and tagged with a satellite device, will be tracked as they bid to make their way back to their wintering grounds in central Africa.

The birds, who were netted in King’s Forest, near Bury St Edmunds, Thetford Forest and Carlton Marshes outside Lowestoft have each been given a pet name - and members of the public can the follow the progress of Sylvester, Victor, PJ et al via the BTO website.

This latest initiative is part of a BTO project launched in 2011 to find out what is happening to the UK’s cuckoos with the organisation calculating that we have lost almost three-quarters of our cuckoo population during the last 25 years.

Important migration routes

Remarkably, male cuckoos, whose celebrated call signals that spring has sprung, tend to leave these shores before the end of June. They can spend as little as two months here, so finding out what happens to them during migration and on arrival in Africa is vital in piecing together the picture.

Over the past seven years, the study has already identified important migration routes via stopover sites in northern Italy and southern Spain, and the precise wintering locations in the Congo rainforest - information that was unknown prior to the tracking campaign.

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Mortality of cuckoos taking the route via Spain has been linked to population decline within the UK, but what scientists at the BTO would like to know now is how successful our cuckoos are at making it to and from Africa in different summers, and, specifically how relatively important are conditions here in the UK and southern Europe in contributing to a successful crossing of the mighty Sahara desert.

Sherwood cuckoo PICTURE: Chris Hewson

Sherwood cuckoo PICTURE: Chris Hewson - Credit: Archant

Unanswered questions

Lead scientist on the project at the BTO, Dr Chris Hewson, said, “This has been an incredibly exciting project identifying, for the first time, where our cuckoos go for the winter, how they get there and how survival during migration appears to be contributing to their population decline.

“But we now need to delve a little deeper to see exactly how they interact with their environments along the way. In a wet, cold summer here in the UK, are our cuckoos less likely to successfully get to their wintering grounds? Or, are conditions in southern Europe, where the cuckoo make final preparations to cross the Sahara, more important?

“These are the kind of questions we would like answers for.”

Only adult male cuckoos, with the exception of one female bird, have been used in the project because they are big enough to be fitted with a tracking device. The tags are solar-powered, transmitting for 10 hours and then going into ‘sleep’ mode for 48 hours, to allow the solar panel to recharge the battery.

Heading abroad

Cuckoo with food - taken at Minsmere PICTURE: Brian Smith

Cuckoo with food - taken at Minsmere PICTURE: Brian Smith - Credit:

The initial years of the study - 2011 - 2014 - threw up some incredibly useful information. The BTO found that cuckoos either migrated southwest via Spain and Morocco (the ‘west route’) or southeast via Italy or the Balkans (the ‘east route’) before converging in the Congo basin of central Africa.

Birds taking the west route left eight days later on average than those taking the east route. Interestingly, birds on the west route were more likely to die before completing the Sahara crossing, even though their route was 12% shorter to this point, demonstrating route-specific costs of migration for the first time.

Despite the obvious geographical barrier presented by the Sahara, most of the mortality on the west route occurred in Europe, suggesting the conditions at stopover sites are responsible. In recent years, Spain has suffered droughts and wildfires, which might have affected the cuckoos, although the BTO says other factors like large-scale habitat change might also have played a role.

The five Suffolk cuckoos contributing to the latest phase of the project are part of a group of 14 birds from the UK currently being tracked. Cuckoos based in Sussex and Hampshire are already in France but as aeenvironment went to press Suffolk’s cuckoos were still in the UK.

Anyone can follow these birds as they make their way south, by viewing the BTO’s interactive map at