Red winged blackbirds are nesting right now, that's why they're so aggressive in the spring. They get mellow after the fledglings grow up, leave the nest, graduate from birdiversity, rack up huge student loans and move back in...

One road we used to ride on south of Calgary years ago had a pair of hawks nesting beside it every spring for 3 or 4 years (it's all suburban houses there now). Far scarier and larger than blackbirds! A friend of ours had talon marks in her helmet shell where one of the birds swooped down and clawed her. My husband decided to draw faces on ovals of paper and tape them to the back of our helmets, as he'd read somewhere about Africans doing that to protect themselves from lions attacking from behind. It seemed to work.