iBird Pro ($0.99 for iPhone and Android; $2.99 for iPad)
iBird Pro offers information on over 900 bird species from North America and Hawaii. It will help you identify birds by numerous attributes, such as size, flight pattern, range, habitat, foods they consume, nesting details and more. In fact, the app even comes with more than 5 hours of audio bird songs and calls, taken from the Macaulay Library at the Cornell Lab of Ornithology. High quality field photos are also provided, and updated with each new version of the app. You can share your favorite birds via Facebook, Twitter or email directly from the app and favorites and notes can be synced across devices automatically. Note that you will need an internet connection to access some parts of the app, such as the reference guide.
Birdwatcher's Diary ($12.99 for iPhone)
If you want to keep precise track of all the birds you see and hear; this (somewhat pricey) app will help. Birdwatcher's Diary even lets you specify whether you actually saw the bird or just heard it. Bird counts are similarly easy to record, simply by tapping the screen. Time and locations, in turn, are recorded automatically, and can subsequently be visualized on Google Maps. Once you have recorded your sightings, you can sort them by name, bird-banding code, time seen or taxonomic order. The fact that you hardly have to use a keyboard makes it easy to use in the field.
U.S. Birding Checklist ($3.33 for Android)
U.S. Birding Checklist is part of a series of Android birding checklist apps, which includes versions for Australia, New Zealand, UK/Europe, Norfolk/Lord Howe Island, and Ecuador/Peru/Bolivia. The U.S. version includes basic identification on 1,040 species and 15 subspecies. It is intended for users who already are familiar with the birds and not as a replacement for a field guide. Experienced bird-watchers can use the app to log bird sightings and upload these to eBird or a similar recording system. The app includes bird photos and sounds, but those must be downloaded separately via your PC. You can get a feel for the app by trying the free demo version first, which has fewer features.
Sibley eGuide to the Birds of North America ($19.99 for iPhone and Android)
The Sibley eGuide app offers identification information on 831 species of birds, each of which is shown in several photos: perched, and in flight from above and below (in total, the app has over 6600 images). Subspecies and regional variations are also catalogued. Detailed maps show migration habits. The app makes use of every inch of the screen, allowing you to compare two images, maps and even sounds side by side. Beginning birders can try the free version first, which includes only 30 species.
National Geographic's Handheld Birds ($9.99 for iPhone)
National Geographic has been a go-to source for information on nature, and now its best-selling book, National Geographic Field Guide to the Birds of North America, has an app to go with it. Equipped with over 1,600 images and 650 range maps, the Handheld Birds app will help you identify birds by family, features, plumage, similar species, habitat, conservation, voice, foraging and reproduction. You can search 867 different North American bird species by name, as well as by taxonomic and family order. Like with iBird Pro, the Cornell Lab of Ornithology provides more than four hours of song and call audio.