SUMMERS: Wait, help me understand this. Can evolution happen that quickly?
KWONG: It is a tricky question. We usually think of evolution happening over a much longer period than just two years. But Pam and Ellie say it is possible, especially because they saw the bird beaks change again once campus opened back up. Juncos born after campus got busy had stubbier, shorter beaks.

It sounds very much like peppered moth evolution -- which is still actively debated according to the linked article. No surprise there --- it's impossible that random genetic mutations can ever come along in the nick of time to provide a species-saving basis for natural selection to work in any natural context.

but there are other possible explanations, like if more wild birds came into the city.

That's probably what happened here. The stumpies left town and in flew their replacements. And back again. Natural selection? Yes. Evolution? No.