Thanks! This is an amazing article. I remember walking on Twin Peaks in the late 1980s, listening to the white-crowned sparrows. The trill at the end has changed since then – it’s less defined and more truncated. In fact, I feel that the whole song has become less clear.
I wonder if population density (hence, competition among the males) might also have something to do with it.
golden gate park: views from the thicket 
Thanks! This is an amazing article. I remember walking on Twin Peaks in the late 1980s, listening to the white-crowned sparrows. The trill at the end has changed since then – it’s less defined and more truncated. In fact, I feel that the whole song has become less clear.
I wonder if population density (hence, competition among the males) might also have something to do with it.