I think the joy of Winged Migration hinges partly on not knowing how they did it. I didn’t realize the process* until I’d watched the featurette on the DVD. If I’d known in advance, it would have still been amazing, but not ‘HOLY SHIT, HOW DID THEY DO THAT?’ amazing.
Highlight below to read the spoiler:
[color=white] The birds were raised by the filmmakers specifically so they could get close to them with camera-carrying ultralights. [/color]