Predatory Scrub Jay

Once again a news item from my sister's house in San Ansemlo, California, where she caught this video of a Western Scrub-Jay attacking (and apparently killing and intending to eat) an another bird:



The prey bird is an LBJ, hard to tell if it is a House Sparrow or House Finch. I don't recall ever having seen a jay go after a live, adult bird like this. My sister describes a "thump" on the window just before seeing the incident; this could have been the LBJ smacking the glass and being stunned, leaving it more vulnerable. Even so, it is quite surprising to me that the jay would swoop right in on it like this. The jay seems to have some trouble finishing the LBJ off, not appearing to be fully equipped for the task.