We see it often with crows (and seagulls) they just protect their area.
I was once attacked by 3 seagulls because we had to moor to a pole were they build their nest :S
I didn't like it :)
It was traumatic, but something I can look back on & laugh at. I guess those $.10 crickets looked like poo on a plate compared to a young, tender $45 morsel.