Ample scientific evidence exists that show that birds are extremely smart and crafty. Some are able to make and use sophisticated tools in ways that chimpanzees can't while others can remember the location of far more caches of food than humans for a long period of time (see also).
Now we've just learned that pigeons, after a year of intense training, "can learn abstract rules about numbers, an ability that until now had been demonstrated only in primates." They "learned to rank groups of one, two and three items in various sizes and shapes. When tested, they were able to do the task even when unfamiliar numbers of things were introduced. In other words, having learned that two was more than one and three more than two, they could also figure out that five was more than two, or eight more than six."
One of the researchers was surprised by these findings but to me (and I expect to others) they're not all that unexpected given what we know about what's called anti-predatory vigilance or sentinel behavior, In many different species of birds individuals change their patterns of scanning for predators (their head is up and they're looking around to see who's there) and feeding (their head is down and they're feeding on seeds or other food) depending on group size, A general finding is that the larger the group, up until about 7-8 individuals, the less time an individual spends scanning for predators and the more time he or she spends feeding. It's assumed that individuals can't scan and feed at the same time and this seems to hold true for many different species. These data, the inverse relationship between group size and time spent looking around for danger, clearly show that birds are able to assess the number of individuals in their group and alter their behavior accordingly. So too do mammals.
Group size is but one variable that influences scanning and feeding. The geometry of a group is also very important. In our study of vigilance in Western evening grosbeaks we discovered not only do birds change their behavior depending on group size but they're also sensitive to the geometry of the group of which they're a part. Individuals organized in a circular array in which they can see all other individuals behave very different from individuals organized in a line in which they can only see their nearest neighbor(s), a maximum of two individuals.
Our results based on detailed video analyses are summarized as follows: "Vigilance (scanning) and other behavior patterns were studied in free-ranging Evening Grosbeaks (Coccothraustes vespertinus) at feeders to assess how flock size and flock geometry influenced the behavior of individual birds. The present results indicate that the way in which individual grosbeaks are positioned with respect to one another effects many aspects of their behavior, especially when a flock contains four or more birds. Birds in a linear array who have difficulty seeing one another, when compared to individuals organized in a circle who can easily see one another, are (1) more vigilant, (2) change their head and body positions more often, (3) react to changes in group size more slowly, (4) show less coordination in head movements, and (5) show more variability in all measures. These differences in behavior ... suggest that individual grosbeaks, when scanning and moving about, are visually monitoring the flock in which they are feeding and gathering information about a number of variables including flock size, what others are doing, where others are, which individuals are present, phenotypic features of flock members, food resources, or the location of potential predators. Individuals likely use visual records of the behavior and perhaps the phenotypic features of others, and this information influences various aspects of their behavior."
While these highly trained captive pigeons are demonstrating sophisticated numerical competency, these data only add to what we already know from field work on other species of birds. Specifically, there aren't fixed patterns of scanning and feeding. Rather, birds show flexibility in patterns of scanning and feeding that are influenced by both group size and group geometry. This is not to mean that the results of the research on pigeons aren't important. They are, but they're not all that surprising after all.
Clearly, calling someone a birdbrain is a compliment. Bird brains are very active and their cognitive abilities rather remarkable and highly evolved.
