Cuckoos tagged with GPS trackers

Cuckoo with GPS tag (Image: BTO) The tiny GPS trackers weigh just five grams

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Scientists from the British Trust for Ornithology are planning to attach tiny satellite trackers to cuckoos to study their migration patterns.

The UK has lost about two thirds of its cuckoos in the last 25 years.

Dr Chris Hewson, the scientist leading the project, says that tracking the birds will reveal more about the habitat they rely on.

The team will tag five male birds with trackers like tiny backpacks that weigh just five grams.

The tags have soft straps which fit around the cuckoos' wings.

"We'd eventually like to tag many more, but each tracker costs more than £2,000," said Dr Hewson, a research ecologist at the BTO, which is based in Thetford, Norfolk.

"But those five should give us brand new information," he told BBC Nature. "At the moment, we don't know what cuckoos do when they leave Britain - how they move around, where they go and when."

The BTO monitors cuckoo numbers - using programmes from an analytics company called SAS - to combine all of the census data on the birds. But this is the first time cuckoos in the UK have been tracked - a project funded in part by the BBC Wildlife Fund.

Common cuckoo (Image: photolibrary.com)
  • Cuckoos are brood parasites. In the UK, they lay eggs in the nests of dunnocks, reed warblers and meadow pipits
  • One female can lay up to 20 eggs in one breeding season
  • The birds look like sparrow hawks and their appearance is thought to intimidate their hosts
  • Cuckoos also fool their hosts with egg "mimicry". Their eggs' colour and markings resemble those of their victims

The birds only spend a quarter of the year - from mid April to mid July - in this country, and the team hopes that the data generated by the project will shed light on what is causing their decline.

"It should show some of the threats they face," said Dr Hewson.

"We might even be able to look at where the birds are dying as these [solar-powered] tags should last for two to three years and (from what we know about their survival rates) we would expect some of our birds to die within that period."

The GPS trackers will communicate their whereabouts via a satellite-based system called Argos, which was specifically developed to collect environmental data and has been adopted for several wildlife tracking studies.

"Each device will switch on for 10 hours every two days," explained Dr Hewson.

"It will then transmit a signal to the satellite and, as the satellite moves, the signal will change so that the position of the device can be worked out."

But before this miniaturised technology can be fitted onto the cuckoo, the birds have to be caught.

Bird in hand

Catching a wild bird is an unpredictable task. The team uses a stuffed female cuckoo as a lure, which is glued onto a perch. They play a recording of a female cuckoo's "bubbling call" to spark the males' interest and a large net hung around the lure acts as a humane trap.

The hope is that the males will fly into the net to reach the female.

Stuffed female cuckoo, used as a lure to catch wild cuckoos for tagging A stuffed female cuckoo acts as a lure to trap male cuckoos

"It can take anything from 10 minutes to several hours to catch one," said Paul Stancliffe from the BTO.

"And there's only a brief window during late spring when cuckoos are looking for a mate and will be interested in the call because they're looking for a mate."

Following several weeks of very early mornings - the team sets up its first catching net just before dawn - they have managed to fit all five birds with tags.

They have caught 10 cuckoos in order to find five that were large and heavy enough to carry the tags.

"To make absolutely certain we're not harming the birds, we only tag males that weigh more than 115g," explained Dr Hewson.

These five birds will send their data back to the BTO where the organisation will publish it on its website, so that the public can follow the progress of the migrant birds.

The researcher suspects that climate change could be driving the birds further north, because the population in Scotland is much more stable than in the rest of the UK. The tags could reveal whether or not this is the case.

"Any information about where they're going and what they're doing will be helpful," said Dr Hewson. "Especially if we can identify the specific habitats they use and how those have changed."

BTO scientist sets up a cuckoo net A net surrounding the lure acts as a humane cuckoo trap

"If you don't understand what's going on, you don't have a chance of working out how to conserve the bird."

Grahame Madge from the RSPB welcomed the study.

"We need to investigate this decline very urgently," he told BBC Nature.

"We have a real blind spot with summer migrants and this satellite tracking technology is helping us shine a torch into these dark areas.

"The cuckoo is one of our most widespread and familiar summer birds. We all associate its call with the onset of spring. So the idea of losing it is very worrying indeed."

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