This is hands down one of the best bird identification apps in the App Store. It has an amazing library of birds, and I havent yet stumbled upon a bird that I wasnt able to find. It also has an intuitive filter to help you find birds based on such things such as the region and time of year.
But the best part of the app has to be the journaling aspect. You can record the birds you see along with info such as weather and location. Other unique features make this a must have for both expert and a amateur birdwatchers. Two thumbs up!
foreign_goods about National Geographic Birds: Field Guide to North America, v3.5