I have the Southern edition of iBird Explorer. The edition contains a lot of birds that you would typically see in a western edition of a book key. While this isn't necessarily a problem it would be great if there was a way to hide them. Much like the favorites button but in reverse. When I see a bird in the list whose range is Texas/Mexico for instance, one which I know I would most likely not ever see here in East Tennessee, I would like to hide it. Hide it from my searches and from my list. I should have a way to retrieve it later if I want, say if I'm visiting Texas, but otherwise I shouldn't be able to see it.
My thinking is that in book form you have to accept the fact that you are going to flip through pages of birds you will most likely never see if you don't visit the locale of that particular bird. But in an interactive app you should be able to customize it to your particular taste and location. Localization is key.