Please find this interesting link to important work on Cuckoos done by Kasper Thorup and his team in Denmark.
They were able to tag and therefore track fledgling cuckoos. This work is very important as the major question for us is, how does a fledgling cuckoo find its way to its wintering grounds in the Congo basin when clearly its parents have long since left, so there is no-one to guide them. Prof Thorup kindly said, “And, I am as confused as you are as to how the young cuckoos find their winter grounds!”