I recall the story of the Crows who frustrated an English Lord by being able to count to 12.
My experience is more mundane.
I was waking along a treed pathway when I noticed a Steller's Jay fly in to observe me. As I always carry some food for birds, I reached in the bag and pulled out an almond, showing the nut to the Jay. Right away, he perked up, indicating his interest.
So I flicked the almond onto the path about 5 meters away from me. The Jay was studying the terrain when some walkers came by and the Jay flew away. I waited a minute or so and as I expected he returned.
I showed him another almond and flicked it in the same direction as the first one. Then a third one. This was too much temptation for the Jay and he glided down to the path, hopped around and picked up all three almonds before flying off. That is, as soon as he had grabbed the third nut, he flew off. He didn't bother looking for any more. He knew there were three nuts and he had them all.
So I concluded that he could count to three.
This is the bird.http://www.flickr.com/photos/birdbug3/