We recently had a Common Swift passing through Hong Kong, just the third record for HK.
These birds breed in north China including Beijing, and winter in southern Africa. What route they take between has been guessed at but was uncertain - until now.
Beijing birds fitted with geolocators in summer 2014 have recently been recaptured and their migration route found - west around the Himalayas before going south to Africa.
Which is why we see so few here in Hong Kong. Our birds were way off track. See here
http://www.birdguides.com/webzine/article.asp?a=5047
including our friend Terry Townshend.
As I send this from my daughter's conservatory in a UK garden, I can see Common Swifts flying outside. They too spend the summer in southern Africa and have recently arrived back here in UK for a few months in summer to breed.