Listening to a Continent Sing

Another yellow warbler in dawn song, the neighbor heard in ID-309, also chipping with considerable energy between songs. But how tame compared to what his neighbor is doing. I find only four different songs among the 34 songs in the nearly three minutes here, in the following sequence (first occurrence of each song in bold):

Minute 1: A A B A B A C A A A A C

Minute 2: A B A B A A A A A A B C A

Minute 3: A D B D B A C A A . . .

He seems to like song "A" in this selection, but ten minutes later he could well favor another of the dozen or so different songs he'll undoubtedly sing during the dawn chorus. I'd be surprised if he has only four different dawn songs.

Tame compared to his neighbor, yes, but why? What is in the heads of these two birds that makes them sing so differently?

Background

Spotted towhee, cattle, mourning dove, ring-necked pheasant (0:54), warbling vireo, another yellow warbler

Photo by John Van de Graaff