Poor polar bear's nose! I once got dive-bombed by a mama red-winged blackbird as I was riding my bicycle past a marshy field -- and here I was calling back to her, earlier -- imitating her "chuck-chuck" call -- she obviously regarded me as a threat to her nestlings. But --- ow! -- that fly-by certainly left a mark!
Reading about this behaviour further, I discovered that "they don't get aggressive until they are well into the breeding season and have a nest to protect. They are highly territorial, aggressive to almost anything that comes too close, especially things that are bigger than they are and that they see as a threat, including hawks, crows, cats and people."