Song Sparrow Song Diversity

How diverse are Song Sparrow songs?

Recently I heard one sing a classic song, then end in three trilling notes;
on the way back from lunch today I heard one sing two opening notes like a
Vesper, then continue as normal.  Do they learn from other sparrows near
their territory?  Do juveniles struggle with their initial songs?  Is
hybridization an issue?

(Hard to admit I know so little about a common songster - although am
comforted by Kenn Kaufman's admission a number of years back that he
couldn't adequately describe a BC Chickadee to his own satisfaction.)

Good birding to all!

Al Schirmacher
Princeton, MN
Mille Lacs & Sherburne Counties

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