In the past 3-4 weeks, I have observed young grackles in groups of 3-5 eating young house finches, sparrows etc. I have never seen the actual hunt, and only come upon the sad sight when I see the birds gathered around the dead bird. Is it common for grackles to "hunt" for live food, or would I be more correct if I blamed the stray cats for killing the birds and the grackles just take advantage of "fresh food"?
I doubt that grackles would attack and kill a healthy house finch. I suspect that they can across the dead or dying bird, and acquired some protein from it.