We place bird sounds in any of three categories: s = song; c = call; u = unspecified. A particular recording may include all three.
In ornithology, a song (s) is generally defined as a vocalization used in primarily territorial and mate attraction/retention contexts. Calls (c) include all other categories of avian vocalizations. Thus, while the most complex and beautiful avian vocalizations are songs, this category can also include harsh and simple sounds. Calls can often be attractive to our ears as well, but typically they are simpler and often harsher than songs from the same species. While in many species it is easy to distinguish songs and calls, in many others it is difficult or impossible for humans to do so, particularly in sound recordings when the bird cannot be directly observed. We have generally used “song” when a vocalization clearly falls in this category, and “call” for all others; however, consistency in this matter is seemingly impossible to achieve, particularly in a group effort such as this. We have therefore begun to indicate in the “details on type” field if there is considerable uncertainty as to whether a given vocalization is a song or a call.
Most birds make a variety of non-vocal sounds, intentionally or otherwise, and Project AVoCet includes all such sounds. Numerous species of birds use mechanical sounds in a song context, for example drumrolls of woodpeckers; air sac-popping, tail quill-rattling, and foot-stamping of some grouse; drumming of snipe, in which air rushing between tail quills creates a pulsed sound; cracks, pops, and whines produced by wings of manakins, etc. Foraging birds may make noises, such as the tapping of woodpeckers; twig-breaking of feeding hornbills; or seed-cracking of parrots and grosbeaks. Many birds routinely make wing sounds in normal or escape flight, and these can be highly characteristic. Nest-hole-excavating woodpeckers, splashing waterbirds, walking penguins, and many others round out the inventory of bird sounds. While most of these sounds would not be useful in playback or for taxonomic analysis, for example, they could be biologically informative and hence are all candidates for inclusion.