White-crowned sparrow (Zonotrichia leucophrys), at the Riparian Preserve at Water Ranch, Gilbert, Arizona.
I love the common little birds. Sometimes they turn out to have uncommon abilities. These sparrows sing songs built of snippets and themes from the songs of birds they are exposed to when very young. Consequently, song dialects can emerge, and if a cohort is in an area where two distinct white-crowned dialects overlap, birds in that group will become fluent singing both songs.