The Space Eagle (morphed from Mighty Eagle) is a special bird that can only be used if you have tokens which you either earn by defeating boss characters or buy through in-app purchases.

More Space Eagle tokens cost:

20 Tokens - $0.99
80 Tokens - $2.99
280 Tokens - $7.99
980 Tokens - $19.99

When you use a token a can of Sardines is launched which will create a wormhole. The Space Eagle will appear from this wormhole and destroy everything in it's path.