Why do they do this? I assume it's the hormonal effects of the seasons changing. Why do the chased birds flee? If you had an olive-green hornet of a bird with a dark crown, white eyelines, a stout bill, and red eyes flying directly toward you, would you sit there on your comfy perch yawning? Or would you head for deep cover?
The next sound I heard, after a "stop-chasing-me!" squeal was a sickening thunk. And a bird fluttering to the ground beneath the large glass windows of the studio.
I summoned Julie and she, after searching the ground in the flower bed, found a male yellow-throated warbler, slightly stunned by its glancing encounter with the window.
Each fall we get a number of yellow-throated warblers on our ridge-top farm. They seem to want to see what the view is like from the top of the ridge. This vantage point certainly offers more of a view of the landscape than their sycamore-tree habitat along river bottoms and creek beds. As a young birder in the early 70s, I knew this species as the sycamore warbler.
Our bird-strike-susceptible windows have FeatherGuards on them which help to reduce the number of window strikes by a large percentage. Still there is no stopping a panicked warbler with a heat-seeking vireo on its tail. Fortunately the strike was at a severe angle, so the impact was not forceful, and the warbler was already recovering when Julie picked it up. She held it for a few minutes to make sure it was on the mend (Julie is a licensed bird rehabilitator), then placed it in our birch tree.
Birds that have hit a window always appear dazed. They gape (bill open) and blink slowly. This male yellow-throated gathered his wits slowly but methodically, so we knew he'd survive the impact. (Many birds suffer a head trauma sufficient to kill them long after the impact).
Recovering birds often gape while gathering their wits.
The following day, a male yellow-throated warbler stopped by our birch tree and spent about 20 minutes preening and chipping in the open. We thought it might be our same bird, come back to visit the scene of the accident.
He was in fine form, preening and foraging along the branches like any healthy member of his species would do. He LOOKS like the same bird, but of course, we can't be sure.