Random check of a couple of song books shows that the tonic note is the highest note of songs fairly often, but frequently it's the second or third degree of the scale. Also quite often, the starting note and the song's lowest note is the root of the V chord (dominant), which then jumps up to the tonic note. I also found a fair number of songs in which the lowest note is the seventh degree of the scale (half-step below the tonic).

It all appears to be pretty random to me. I don't know if this sort of statistical analysis is very useful. You pretty well have to take it song by song.

Don Firth

P. S. Sometime way back in the late 1950s, there was a series of television shows by Leonard Bernstein explaining music to kids (also watched by a lot of adults, because Bernstein explained things very clearly and entertainingly). I especially recall one program where he went through an amazing number of pieces, classical, popular, folk, you name it, that started with the first four notes of the song "How Dry I Am." Low 5 up to the tonic, then 2 and 3. Same four pitches, and when you start altering the rhythm a smidgeon, it covers a huge amount of music.