BTW, there is a chap in Hampshire who could be the new David Attenborough. His name is Darren Naish. 8-P
He just written about playing in birds in his blog. I just realized: how much did Springwatch show birds, or mammals, at play? Would be interesting to watch!
I agree. There's quite a few scientific papers on play in birds available online. I posted links to some on a thread here one time but can't find it.
I've seen a hooded crow repeatedly dropping and catching an object (probably a stick) in flight- this behaviour is found in corvids, raptors, gulls and terns at least and now seems to be generally described as "drop-catch play". There was an excellent study done of the behaviour in herring gulls that more or less confirmed that their behaviour was true play.
Drop-catch behaviour is play in herring gulls, Larus argentatus. See link below...
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W9W-45BC8DN-BK&_user=10&_coverDate=02%2F28%2F2002&_rdoc=1&_fmt=high&_orig=browse&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1f68c6209928ce891f82e6408f41042a
I've also on more than one occasion seen both single swallows and groups of swallows (and once an attendant house martin) dropping and catching feathers in flight. This behaviour in hirundines is sometimes regarded as play (particularly if juveniles are involved) but can also be a form of competition over nesting resources.
Other forms of play are well documented in corvids and parrots. There were some great anecdotes on the thread on here which included juv. starlings picking up a feather and running around chasing eachother and herring gulls on a roof-top colony throwing sticks to eachother!
Sorry for the ramblings, bit off-topic, but such behaviour would be nice to see on film.