Only app I have spent real money on - no regrets.

This is my go-to app for birds and it has never let me down. As others have mentioned it takes up a lot of memory so updates can be a hassle. When I update my phone I now make sure I get lots of memory- for songs, photos and this app it is worth it. I especially like the song feature because I often can hear, but not clearly see a bird. The song helps me pin the ID. Once I even used it to try to get a kestrel back to her young. Whether its looking at me feeder or on a hike this app is wonderful. I tried the Audubon app but this is much better. I tend to be cheap about apps but this was over $20 and I love it.

ZooMommy about iBird Pro Guide to Birds, v9.1