My Dad used to say that they come back to the place where they were born. The cuckoo`s offspring came back to our woods every year for years and years. Then something broke the pattern - maybe the bird didn`t survive the journey and we never heard them again. I haven`t heard the cuckoo for at least 15 years.
Heard one a couple of years ago, but none recently. They have started clearing the rhines more regularly and in so doing have cleared the reed away from the banks, result, no Cuckoos anymore. :-(