I have always marveled at the behavior of momma killdeers when the nest is in danger.
We have Mocking bird in our neighborhood that during nesting season every year stalks my 85lb Rhodesian Ridgeback. This tough little dude has bit my dog's butt more than once and he's almost been chomped for his efforts a few times. If the dog's in the front yard, the bird uses a street light as a base for his attacks. If the dog's in the house, this little brute will go from window to window to challenge the dog through the glass. Fun to watch.
I've also seen a Mocking bird purposely dive into the grill of on coming car to attack it. That one didn't go so well...