
A flock of dowitchers taking off from Montrose Beach.
I am not sure whether they're long- or short-billed dowitchers, most probably short-billed. I am not sure how common they are migrating through Chicago but I saw this flock on Montrose Beach in May 2007. I saw them approaching, they fed on the beach for about 5 minutes and then flew off. Their summer homes are in Canada and Alaska and they winter in Southern US to as far as Brazil in South America.
More information from All About Birds.