What’s going on when I see little birds going after a big bird?

It’s called “mobbing”: smaller birds swooping and calling aggressively at larger birds (and sometimes mammals). Small birds typically do this to drive away potential predators from places such as their breeding territory, a nest or young, or a nonbreeding home range.

Common mobbers include chickadees, titmice, kingbirds, blackbirds, grackles, jays, and crows. Common targets of mobbing are hawks, crows, ravens, herons, and owls. Mobbing can happen at any time of year, but it is especially common in spring as birds experience surges of hormones, become territorial, and begin to nest.

Three Kinds of Mobbing

• Protecting territories or food sources. For example, in the early spring Red-winged Blackbirds chase not only rival blackbirds, but almost any other bird, big or small, that crosses their territory.
• Protecting themselves and their young from predators. In these cases you often see a single smaller bird chasing a larger bird in flight (sometimes two or three join the chase as the larger bird crosses territories).
• Group mobbing to drive away a predator. When a predator such as a hawk, owl, or crow perches in a habitat, multiple species may join forces to mob this common threat. The mobbing birds tend to use similar-sounding call notes, regardless of their species, and this may recruit other individuals to form a mobbing flock. It’s this phenomenon that’s behind the success of pishing, in which a birder imitates mobbing calls to bring birds into view. Our Birding Warblers video features a segment on pishing.

Other Benefits of Mobbing

The sharp, intense sound of mobbing calls has a few side benefits. It may warn other small birds or encourage them to join in. It informs the predator that it’s been spotted and has lost the element of surprise, encouraging it to move to another area with unsuspecting prey. And the loud, persistent calls can even draw in larger predators to go after the target of the mobbing.

Owls in particular elicit intense mobbing behavior, as they often prey on sleeping birds. Smaller birds chase these predators out of their territories so they will be safer at night. Owls are such frequent targets of mobbing—and so hard to see otherwise—that listening for mobbing calls is a good way to find owls during the day.

Mobbing usually does not harm either party—the small bird doing the mobbing or the larger bird being mobbed. You may see blackbirds or kingbirds making contact with crows, hawks, or herons as they drive them off, but it’s more aimed at driving away a predator than causing it injury. And for smaller birds, mobbing is not as dangerous as it may look. The lack of surprise, and the greater maneuverability of the mobber, take away much of the predator’s advantage.