The Birds in your Garden

It’s a while since I last wrote about the British Trust for Ornithology’s major Cuckoo tracking project, so I thought that an update might be of interest.

Cuckoo wearing it's satellite tag - BTO

Cuckoo wearing it’s satellite tag – BTO

The project was initiated in 2011 to find out why we had lost around two thirds of our Cuckoos in the UK. The BTO has been fitting them with satellite trackers and have discovered much, including pinpointing for the first time their wintering grounds in the western Congo rainforest and discovering that they use two routes, one via Italy and one via Spain, to get there.

This is the first time birds have been recorded taking two distinct routes to the same destination – usually route divergence leads to different wintering grounds. Interestingly, all of the birds return to the UK via the western route, regardless of the route used the previous autumn.

The study has revealed that the route a Cuckoo takes to the Congo can mean the difference between life and death. BTO scientists compared the mortality rates associated with the two and found that birds travelling via Italy had a far higher survival rate than those travelling via Spain.

They also found that all the birds tagged in Scotland and Wales, where the species is not doing as badly, took the more successful eastern route via Italy. Whereas in England, where we have lost 71% of our breeding Cuckoos during the last 25 years, local populations were made up of a mix of birds using the two routes. Significantly, the proportion of birds using the less successful route via Spain correlated strongly with population decline in each location studied.

Cuckoos fuel up for their long flights by storing fat, which those feeding in Spain might be finding harder to do than those in Italy. This could be a result of climate change, for example the recent late summer droughts in Spain, reducing the abundance of the high-energy invertebrates that the Cuckoos need to fuel a desert crossing. The study also suggests that birds going via Spain may fatten-up more in the UK before they begin their migration than birds flying via Italy. This would leave them especially vulnerable to the recent severe decline in moths in the south of England, their caterpillars being the Cuckoos’ main food source.

Eight new birds have joined join the four surviving individuals tagged in previous years, and BTO scientists will be watching all of them as they migrate to Africa and back over the next few months.

They will be concentrating on how the birds interact with a weather system called the Inter Tropical Convergence Zone (ITCZ) as they prepare to make their way back next spring. The drought-busting rains that this system brings to West Africa in early March may be vital to the success of onward migration from countries such as Sierra Leone, Ivory Coast and Ghana.

As an interesting sideline, in May this year, hundreds of Chinese schoolchildren took part in a competition to choose the name of a pioneering Cuckoo that would help uncover the migrations of Cuckoos from the Beijing area. Flappy McFlapperson was the winning name!

Flappy left Beijing in June and headed north into Mongolia, crossing the Gobi desert to spend the ‘summer months’ in the Onon-Balj National Park, the birth place of Genghis Khan and very close to the Russian border, moving on in autumn migration mode: destination unknown – possibly Southeast Asia, India or even Africa. All being well, during the next few months Flappy’s wintering location, will be unveiled for the very first time.
Mike Gray