Pallid Cuckoo

Thanks to Bill and Chris.

My assumption, possibly wildly in error, was that the immature had to be
one year old, and that a cuckoo would only feed its own offspring.  Surely
it is too early in the season for a Pallid Cuckoo to have an immature
(not fledgling) offspring?  This would imply that they either return to the
same area each year, or they travel as family groups. 

I'm sure these questions are long since answered, but couldn't find any
information to answer this in the general literature I have available.  
Is the National Photographic Index book on cuckoos the best general work
currently available?

Cheers, Rob
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