Recently an avian brouhaha in the forest behind my house drew my attention. Looking up through the bare trees toward the top of the mountain, I could see a red-tailed hawk flying south just below the ridge and another circling down in my direction and then veering off to join what was likely its mate, chased by several loudly cawing crows.
In banding together to drive off this much larger predator, the crows were exhibiting a set of common behaviors known as “mobbing.” Rather than one David facing down Goliath, there are many Davids, spreading the risk from one individual to many through cooperation. Zoologist Konrad Lorenz first described this behavior in his 1966 book, “On Aggression,” a seminal work that explored aggression in animals and humans.
Mobbing often starts with one individual that becomes aware of a potential predator and responds through any of several mechanisms that draw the attention of others in its species, forming a mob. “Something about the target arouses a fierce, contagious impulse to attack and destroy,” as Ken Westhues describe in his article “The Unkindly Art of Mobbing” in the fall 2006 issue of Academic Matters: The Journal of Higher Education (academicmatters.ca).
As Tim Caro, professor of wildlife, fish and conservation biology at the University of California describes in his 2005 book, “Antipredator Defenses in Birds and Mammals (Interspecific Interactions),” the effect of mobbing can have diverse outcomes, mostly bad for the predator, such as being struck, pecked or bitten. Fieldfares, thrushes native to Europe and Asia, throw feces at predators during mobbing.
Mobbing can lead to the targeted predator abandoning the hunt, leaving the area or even being killed by the prey. In some cases, the potential predator becomes prey and is eaten. While on rare occasions the predator may catch a mobber, few predators want to risk the wrath of the many when it’s easier – and safer – to go look for lone prey somewhere else.
While actions taken during mobbing are associated with normal defense mechanisms in social animals, they become distinct as mobbing when identification of the potential predator is difficult or flight is not an option, as in protection of young. Some researchers think mobbing may also be a way for adults in a species to teach their offspring which species are predators. Mobbing can also occur in defense of food sources.
Mobbing is most often done within a group of related individuals in a species but can be done in cooperation with other species and can have a chaining effect to individuals outside of the original mobbing group. For example, in the case of the crow-and-hawk clash I observed, by the time the two red-tailed hawks were driven out of the area, the crows hot on their tails may not have been part of the group that started the mobbing.
The evolution of mobbing as a defense mechanism may be one of the driving forces behind birds’ nesting in colonies. It may even be why defenseless species that don’t mob sometimes take up residence close to a more aggressive prey species that does, to benefit from their neighbor’s behavior.
Mobbing seems to be most common among birds, from crows to chickadees. Indeed, “virtually all the empirical data used to test hypotheses about mobbing derive from birds,” Caro writes. This may be because birds, unlike mammals, are more typically hunted during the day, when it’s easier to spot predators and organize an assault on them, he adds. Still, some mammals, insects and even fish will form mobs to drive off predators.
Meerkats, African mammals in the mongoose family, live in burrows in cooperative social groups referred to as “clans,” “gangs” or “mobs.” When threatened, meerkats typically form into tight groups, standing up, to make themselves appear bigger and more dangerous. When grouped like this, they are more likely to mob snakes, foxes and other predators. California ground squirrels, which are also social mammals that live in burrows, will also mob snakes and other predators, kicking sand in their eyes.
Some researchers see the barking of dogs as possibly serving not just as a warning to other dogs that a potential predator or competitor is in the area but also as a way to bring individuals together to mob the threat and drive it off. Bluegill will mob to defend their underwater nests, and some wasps, including yellow jackets, release an alarm pheromone when threatened that triggers their colony mates to swarm (mob) and attack the threat – another good reason for not swatting wasps.
Lorenz thought we humans could control our mobbing instincts through using our intellect, but other researchers see mobbing in many aggressive behaviors more likely to occur in groups, from lynching to bullying to taking on better-armed armies in combat. Westhues’ article focused not on animal behavior but on how academics can gang up on unpopular colleagues.
Lately, the concept of mobbing, and even the word itself, has been applied to the behavior of humans, particularly strangers, when they band together for a variety of purposes. New technology is driving a wave of “crowd sourcing” ideas, and “crowd funding” projects by “cash mobs” over the internet. Through the use of cell phones, “flash mobs” can now form in public spaces with head-spinning speed for activities ranging from giving impromptu concerts to protesting oppressive governments.
Whatever the species or goal, cooperation is more likely to lead to success in meeting big challenges than facing them alone.