Mockingbirds can remember if they've seen you before!

A new study reported in the US journal Proceedings of the National Academy of Sciences has shown that mockingbirds can attack people who have threatened them in the past, proving that they are able to recognise individual humans. 
Mockingbirds can remember people who have threatened them and even start dive-bombing them if they see the person again [...] An urban population of the songbirds ignored most passers-by, but took to the air when they recognised people who had approached their nest days before. When the birds spotted a previous offender, they started screeching and set off to harass the person with swooping dives, at times grazing the tops of their heads.
You can find out more here and here.