大象传媒

The call of the cuckoo is for many the defining sign of spring and has become deep rooted in our culture. But the call is becoming scarce. In Wicken Fen since 1985 numbers have declined by about a half and this isn't an isolated incident. We've lost more than a third in the UK in the past 13 years. But why? To find out you have to see how they live their lives. The first reason is that they lay their eggs in other birds nests and the birds that they depend on are also struggling. The second reason that cuckoos are doing badly is that they feed on moth caterpillars and moths have also declined by a third since the 1960s. Mild springs means that the caterpillars are hatching earlier and may not be around by the time the cuckoos arrive to feed. And finally, though we think of the cuckoo as a British bird, the cuckoo spends two thirds of the year on the African savannah where droughts and shifts in rainfall have further affected it. Cuckoos migrates over 4,000 miles to get back to the UK, crossing over the Sahara - which at its shortest point is still 12,000 miles wide and is still expanding. Many cuckoos simply never make it back. So the causes of its dramatic decline are complex. The cuckoos are a harbinger of wider environmental problems. To lose the cuckoo and its wonderful trickery that has evolved over thousands of years would be devastating.