Have had this DVD interactive computer program for some time now and have to say that it's superb. It shows details and pictures of pretty much any bird which is likely to visit our shores and by opening the split screen (as shown below), you can compare species side by side.
It also shows distribution maps, video clips and has sound recordings for song recognition.
It isn't cheap at £142.95, but in my opinion is well worth every penny and ideal for anyone interested in identifying birds, wouldn't want to be without mine.
http://www.birdguides.com/bwpi/
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