Cassin's Kingbird on the West Campus: Is Spring Early?

(Updated)There were a couple of surprises on our west campus today. I was out for the usual walk at lunchtime and was out in a remote corner of the campus near the drainage pond. There was a bird in the top of the tree that looked out of place, a bird with a certain amount of attitude. It had the yellow breast of the goldfinch, but was way too large, and the beak was wrong. I started to realize that even though spring has not yet arrived, the Western Kingbird (Tyrannus verticalis) has. Postscript: Or is it a Cassin's Kingbird (Tyrannus vociferans)? On reexamination I'm seeing the white tail tips, and lack of white outside tail feathers. Either way, I'm surprised to see one this month. Update: Stanislaus County birders tell me it is a Cassin's.

The Kingbirds are tropical species who only spend summers here in the far north, so I don't know how unusual this might be. Spring may be arriving earlier these days as the climate warms. I'll be watching to see if this one has buddies near by (they tend to be very territorial in the breeding season, though). If anyone can clear this up, I'd appreciate your comments!