British Trust for Ornithology July 2014


Nine members of the Watching Birds Group travelled to the British Trust for Ornithology at Thetford and enjoyed a very interesting talk on cuckoo migration outlined by Paul Stancliffe, their Media Manager. The BTO’s cuckoo tracking project began in 2011 after monitoring of UK cuckoos suggested a huge decline from the 1990s to the present day. Results showed that the Scottish population had actually increased over this period, whilst England had made significant losses. Initial research found that UK cuckoo losses were not associated with their relatively short stay in the UK, nor in the lack of breeding success, suggesting that problems during migration may be a major factor.

Limited tracking of tagged male cuckoos by satellite started in 2011, using tags weighing just 5 grams and costing £2500 each. The BTO has been delighted at the generous support of sponsors and Cuckoo Champions meaning the future of the project seems secure.

Currently, 22 birds are being tracked and anyone can follow their progress by logging into the BTO website As I type this in July some males are already in southern Europe; the website is very user-friendly so do take a peek.

Early results from tracking studies would appear to show that birds which take a westerly route through Spain, which has suffered drought conditions in recent years, have lower survival rates than birds which take a more easterly route through Italy. Interestingly all the cuckoos tagged in Scotland, where numbers are stable or increasing, have taken the apparently more successful eastern migration route.

All birds have to refuel and build fat reserves during migration before moving on, the major obstacle to them is in crossing the vast Sahara desert, where some tagged birds have died en route. Does the easterly route through Italy provide better food supplies than Spain? Notably many of the Italy routed birds have managed to cross the Meditteranean Sea and the desert in minimal hops, lending support to theories of better food supplies on that route.

Tracking has established the main cuckoo migration routes, and also discovered that most birds overwinter in Congo or Gabon, or occasionally even further south in Angola. This fascinating project may yet reveal why our cuckoo population is in serious decline. If results confirm that problems occur during migration, funds currently used to study cuckoos in the UK may be diverted and better used for further migration studies.

If you would like to sponsor a cuckoo, click here cuckoo

Following this insightful talk, Paul led members around the BTO Reserve where all those present had excellent views of kingfishers, a real bonus and a fitting end to our visit.

The group made a donation to the BTO Cuckoo Project and thanked Paul for his excellent talk.

Peter Heath