In our backyards, we're starting to see the formation of "mixed winter flocks" of birds like chickadees, nuthatches, woodpeckers, cardinal, jays, and titmice. This flocking helps protect the birds of the mixed flock from predators. Blue Jays often voice the warning call when there is a predator in the area and birds either flee or freeze. When a large group of birds flee all at once in response to an alarm call, this flushing can also serve to confuse the predator.
Multiple birds together can make the search for food more efficient. They'll be able to locate new food sources, but face less competition for those resources because of the different food preferences and foraging techniques of each species.