In the good old days, before the Internet or newfangled weather modeling, the English knew that spring had sprung when the first ringing call of the cuckoo bird was heard in the countryside. In fact, people would write into the Times of London to report cuckoo bird sightings and share the hope of warmer weather with their cold- and cloud-weary compatriots.
"The extreme and unpredictable weather is killing the birds at several different points along their migration route. Last year we had a cuckoo that died in a freak hail storm in southern Spain in April, as it was trying to make it back to England."
Over the last 15 years, however, the common cuckoo bird has declined by 50 percent in Great Britain. The population in England has been hit the worst, with nearly two-thirds of cuckoos gone, while in Wales there has only been a 30 percent decline. The Scottish cuckoo birds, on the other hand, are apparently doing just fine.
The most obvious culprit in the cuckoos' demise is loss of habitat in England. Scotland's highlands still have native grasslands squirming with hairy caterpillars and Emperor moths, while England is much more developed. Because cuckoos are brood parasites, however—laying their eggs in another bird's nest and leaving that bird to care for them—they only spend about six weeks in Great Britain. That leaves a lot of time for issues in other countries the rest of the year.
Ecologists at the British Trust for Ornithology (BTO) have been tracking the migration of the common cuckoo bird for the past two years to try and get a better grasp on what might be going on during the weeks when the birds aren't in Great Britain.
"Before these studies, we really had no idea what happened to the cuckoos outside of the six weeks when they mate and lay eggs in Great Britain," said Chris Hewson, Senior Research Ecologist at BTO. "All we knew is that sometime around June or July they started flying off to the Southeast and then made a pit stop in Northern Italy. But where exactly in Africa they wintered or how they got there was just not known."
Over the past two years, BTO has fitted a total of 17 cuckoo birds with tiny solar-powered tracking devices that sit on the bird like a little backpack. Hewson now knows that the birds take one of two paths to get to their wintering grounds in the rainforests of the Congo: the eastern route through Italy or a western route through Spain. Once in the Congo, the cuckoos follow the path of what is known as the intertropical conversion zone, a weather system that brings rain from the Equator west through Africa. The cuckoos take advantage of freshly rain-soaked forests to fatten up on insects before they set out on their perilous voyage back across the Sahara to Europe each spring.
The study has shown that birds from England seem to prefer going through Spain, even though that adds an extra 3,000 kilometers to their route. Additionally, none of the cuckoo birds that chose that path last summer made it to the Congo. The cuckoo birds were no match for the extreme drought of the summer of 2012 and the consequent wildfires in Spain.
"Climate change may end up being the biggest factor affecting these birds," said Hewson. "The extreme and unpredictable weather is killing the birds at several different points along their migration route. Last year we had a cuckoo bird that died in a freak hail storm in southern Spain in April, as it was trying to make it back to England."
Climate change is also wreaking havoc on the cuckoos' delicate timing. The rains in West Africa are determined by the movement of the sun in the spring and will remain constant even in the face of a changing climate. Spring, however, is coming earlier and earlier to Northern Europe, which means that by the time the birds have fattened up with the help of the African rains, they may miss the English spring altogether.
Even though the cuckoo's globe-trotting ways may be their undoing, Hewson can't help but love them for it.
"For me, the coolest thing about the cuckoo, is that it truly is a tropical bird," said Hewson. "I think people lose sight of that because they are so ubiquitous in the English countryside come spring. But these birds spend most of the year in the rainforest in the Congo."
"Can you imagine hanging out with gorillas all winter and then spending your spring with a pillar box?" laughed Hewson. "When I listen to cuckoos, I don't just hear spring, I hear Africa."