In “Pigeons on Par with Primates in Numerical Competence” (Science, December 23, 2011), Damian Scarf et al. find,
Although many animals are able to discriminate stimuli differing in numerosity, only primates are thought to share our ability to employ abstract numerical rules. Here, we show that this ability is present in pigeons and that their performance is indistinguishable from that displayed by monkeys.
You have to pay to know any more, but it sounds about right.