What Is Going On When I See Little Birds Pursuing A Big Bird?

Red-winged Blackbird mobbing other species: with Great Blue Heron,
by Larry deWitt; with Red-tailed Hawk, by A wing and a prayer;
with Osprey, by Laura M Eppig; with Bald Eagle,

You saw a behavior known as "mobbing," in which smaller birds swoop and dash at flying or perched larger birds (and occasionally mammals). They usually do this to keep prospective predators away from a breeding territory, a nest or young, or a nonbreeding home range.

Chickadees, titmice, kingbirds, blackbirds, grackles, jays, and crows are common mobbers. Hawks, crows, ravens, herons, and owls are common targets of mobbing. Mobbing can occur at any time of year, although it is most common in the spring as birds experience hormonal surges, become territorial, and begin to nest.

There are various types of mobbing. Birds may attempt to drive other birds away from their territory or food sources. Red-winged Blackbirds, for example, hunt not only rival blackbirds but practically any other bird, big or tiny, that crosses their territory in the early spring.

Birds also mob in order to protect themselves and their young from predators. A single smaller bird chasing a larger bird in flight is common in these circumstances (occasionally two or three join the chase when the larger bird crosses territory).

In other circumstances, you'll come across a flock of birds disturbing a predator perched on a branch. Several species frequently band together to mob this shared threat. Mobbing birds, regardless of species, employ similar-sounding call notes, which may function to attract additional individuals to join a mobbing flock. This behavior is responsible for the popularity of pishing, a technique in which a birder imitates mobbing cries to attract birds into view. A portion of pishing is included in our Birding Warblers video.

Mobbing cries can also serve as a warning to other small birds, attract larger predators to go after the mobbing target, and alert a predator that it has been discovered, causing it to move to another area with unsuspecting prey.

Owls, in particular, cause considerable mobbing since they frequently feed on sleeping birds. Smaller birds chase these predators away from their territory in order to be safe at night. Owls are such regular mobbing targets—and so difficult to notice otherwise—that listening for mobbing calls is a fantastic technique to find owls throughout the day.

Mobbing does not normally hurt the larger bird, though you may witness blackbirds or kingbirds collide with crows, hawks, or herons as they chase them away. However, the activity is related to scaring away a predator rather than injuring it. Mobbing, on the other hand, is not as hazardous to smaller birds as it appears. The lack of surprise, along with the mobber's higher agility, negates most of the predator's advantage.

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