The full list of species is here. Currently the app includes over 200 species of birds, along with 3 species of frogs and toads, and 3 species of squirrels and chipmunks.
For some species the app will identify only a single sound class such as “song”, for other species several different types of vocalizations are covered (e.g. chickadees can be identified by either the whistled song or the “chik-a-dee” call). In general only longer and more complex (more distinctive) sounds are recognized. Short chips and squeaks are not “known” to the app and will not be identified, nor are woodpecker drumming sounds.