Continuity mistake: It is mentioned in dialog that during the last bird attack (the first film), a red rain was visible that seemed to drive the birds mad. However, at no time during the original film is there any red rain visible.
Other mistake: Throughout the film, you can frequently see many people's faces blurred, phone numbers blurred, store-fronts blurred, etc. This is because the production could not afford the rights to show these people, places and things, and simply blurred them out.