Mobbing Behavior in Birds

One Friday at the Desert Museum, another docent and I separately witnessed an interesting interaction between a raven and a smaller raptor, most likely an accipiter (Cooper’s hawk or sharp-shinned hawk).  The larger bird was harassing the smaller one.  It’s more common to see small birds attacking or harassing a larger raptor.  This behavior is known as mobbing, and, although it’s most frequently seen in birds, other animal species use similar tactics.


Mobbing is an antipredator technique used by a prey species against a predator, most commonly to protect their offspring.  The goal of the prey species is to drive the predator from a nest, breeding territory or non-breeding home range, or even a food source.  Mobbing takes place most often in the spring, coinciding with breeding and nesting. Sometimes mobbing is employed to distract and steal food from another bird. Another important function of mobbing is to teach younger birds to distinguish friends from foes. A recent study indicates that mobbing may also give male birds the chance to show off their physical qualities to impress females. 


The most common targets of mobbing include hawks, eagles, crows, ravens, herons, and owls.  Those doing the mobbing (mobsters?) include chickadees, titmice, kingbirds, blackbirds, grackles, jays, crows, ravens and even other raptors.  Mobbing behavior can include chasing, dive-bombing,

bumping, loud squawking, defecating or vomiting on the predator, and may be done by a single bird or a group.  The loud calls often attract more birds of the same species to join in on the harassment. 


Several years ago, I felt very lucky when a great-horned owl chose one of my large trees in which to roost.   It wasn’t long, however, before I began to hear the incessant alarm calling of a Cooper’s hawk.  I discovered the Cooper’s hawk perching nearby and constantly tormenting the owl.  Eventually, the owl moved on to somewhere more peaceful. The Cooper’s hawk, who had a nest not far away, had achieved her goal, removing the predator from the area.  In fact, one way to find perching owls is to listen for the loud calls of mobbing birds. 


By its nature, mobbing by small birds of a large, dangerous predator seems to be a courageous or foolhardy act.  Researchers don’t completely understand why predators don’t turn and snatch up one or two of the tormentors, which would presumably put an eventual end to the behavior. Since mobbing persists, it suggests that surprise is an essential element in raptor hunting. 

Next time you hear loud bird squawking, check the skies for some fascinating bird behavior.

References:

All About Birds: Mobbing Behavior

Mobbing Behavior: Wikipedia https://en.wikipedia.org/wiki/Mobbing_(animal_behavior)

Stanford Birds - Mobbing 

Science Daily: Birds of a feather mob together

https://www.fs.usda.gov/detail/r10/plants-animals/?cid=fsbdev2_038598