It is not always the case that similar birds flock together, although it is often true (think of vast flocks of starlings or strings of Canada Geese). In complex habitats like forests, it is often the opposite: flocks often consist of a few individuals each of many, quite different, species. In the Rocky Mountain winter, the most common combination is the Red-breasted Nuthatch (at left) with Mountain or Black-capped Chickadees, Ruby-crowned Kinglets, Brown Creepers, Downy Woodpeckers, and a few less-common kinds (finches, crossbills, siskins). Why should DIFFERENT species want to forage together in such 'mixed' flocks? There are two common ideas. First, different species feed in different ways, so that individual birds in a mixed flock compete less for food than if all the birds were the same. This is not so different from the human tendency to specialize in businesses that have a distinctive product to offer, especially in a crowded shopping arena. Second, it is often the case that the different species look out for predators in different ways, with some species naturally more alert to distant movements that might be threats. In many cases, these 'finders' give alarm calls that alert the other species to danger. In a recent study by University of Montana researchers, Red-breasted Nuthatches reacted to the calls of chickadees by giving their own alarm calls, even if they could not see the predator.
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