Cuckoos are already on their way

With the latest heatwave behind us (at the time of writing) and the bulk of the summer ahead, it’s not only we humans who are planning our travels to foreign shores. The UK’s breeding Cuckoos are already starting off on their journeys south. It seems like it was a few days ago when we first heard reports of their distinctive calls in various locations across the country, and they are already on their way south.

Just a few weeks ago, wildlife artist and filmmaker Robert Fuller appeared in a series of films while he searched for Cuckoo chicks in Reed Warbler nests in a reed bed on the BBC Springwatch program. His fascinating films gave us an opportunity to look in on the brood-parasitism practice of these brief spring and summer visitors. Shortly after the broadcasts, the first of these visitors was heading off on their often perilous journey back to Africa, where they will overwinter.

Although not garden birds, Cuckoos are widespread and familiar across much of Britain and Ireland, with most people able to recognise their well-known call. As is often the case with many well-known species, fewer of us get to hear the ‘cuck-coo ’call these days. According to the BTO, we have lost more than a third of our breeding Cuckoos during the last three decades.

For many years, researchers at the BTO have been investigating the many facets of these fascinating birds’ lives, seeking to better understand the causes of these ongoing and concerning declines. Much of this research, which uses satellite technology, continues to help scientists at the Trust understand the challenges these birds face as they make their annual migrations to central Africa and back.

This spring, ornithologists have once again been busy catching and tagging Cuckoos in Scotland and England, while their colleagues from The National Parks and Wildlife Service (NPWS) have been doing the same in Ireland as part of an ongoing project launched in 2011.

Over the last 15 years, researchers have fitted satellite tags to more than 140 Cuckoos from around Britain and Ireland. These tags allow scientists to follow the birds ’routes in real time, enabling them to identify potential obstacles and challenges that the remarkable long-distance travellers face as they make their epic journeys across continents. A further nine Cuckoos have also been fitted with highly accurate GPS tags that will allow the experts to see the birds ’routes and habitat use in even more detail.

Prior to this project, very little was known about the Cuckoo’s migration routes, and their wintering areas south of the Sahara were unknown. Among the many important findings so far is the discovery that the birds use two distinct migration routes to reach the same wintering grounds in tropical Africa.

All the Cuckoos tagged in Scotland and the uplands of Wales take an easterly route via Italy when heading south after the breeding season. These birds have proven to have a significantly higher survival rate than those taking the westerly route through Spain. Cuckoos from elsewhere in the UK may take either route. However, research has shown that Cuckoos from lowland England that take a westerly route have the lowest survival rates, especially those that leave the breeding grounds later.

Thanks to the project, researchers also discovered that the Cuckoos often leave the UK to start their ‘autumn’ migration much sooner than was previously supposed. We now know that many male Cuckoos set off after a relatively short stay and can be heading south by early to mid June, having spent as little as six weeks in their breeding areas.