Back in the 60s, there was a study done with pigeons being able to inspect pills on an assembly line[1]. Didn't end up being implemented in a real world scenario, but pigeons are extremely good at recognizing patterns without losing attentiveness over time. There's a pretty good book[2] on pigeon intelligence for anyone wanting to know more about their abilities.

I've an amateur ornithologist (it's a hobby), but never been a huge rock pigeon fan. However, I respect their abilities and how much we underestimate them.

[1] https://books.google.com/books?id=HxU-9UeDCI0C&pg=PA497&lpg=...

[2] http://www.amazon.com/Pigeons-Fascinating-Worlds-Revered-Rev...