Indigo Buntings give a series of double notes. Researchers at Cornell jumbled up these notes and found:
1) order of notes not essential for species recognition.
2) rhythmic cadence and intervals also not essential.
3) parts of song that are constant within species are those that function for species recognition
4) parts that were constant within an individual but vary between individuals = species recognition
Birds react most strongly to calls by the same species. Less strongly to calls from different species. Even less strongly to species in different genera. Individauls react to same species call less with neighbors and more with strangers. One of my students played owl calls to illicit mobbing. She found that birds react most strongly to local owls and to those that eat small birds.