Many of us might have witnessed this pre-emptive behavior but never had the chance or reflexes to record it. Kevin Ebi and Jennifer Owen successfully documented the predator deterrence behavior of crows. This observation is a part of a much larger project. Kevin has spent three nesting seasons with a pair of bald eagles nesting in Heritage Park, Kirkland, Washington and wrote a book.
According to his account the video is from June 12, 2011. Two cameras were used to record the event. Most of the footage is from one attack, but some of the close-ups were from a second attack that occurred about two hours after the first. Mobbing is an anti-predatory behavior in which a group of animals harasses a predator to make it leave the area.
The scientific thinking about the phenomenon was articulated by influential Austrian behavioral biologist Konrad Lorenz. In his seminal 1966 book “On Aggression” he provides a detailed discussion of why and how the behavior might have evolved.
As we see in this video at least two crows are involved in confronting a powerful predator with direct aggression. Dive bombings distract the predator from focusing on a search image such as a nest with vulnerable eggs or nestlings. Engaging a predator directly is a risky behavior and has altruistic and cooperative components. Most predators ambush their prey by surprise attacks. Mobbing helps to advertise the location of the predator and reduce such surprise attacks. Aggressors are cooperating intensely to force the predator to leave. One has to remember that these dive bombing maneuvers can pose a serious threat to the predator. Aggressors will at one point try to defecate and even vomit on the feathers of the predator. Feathers are extremely important and must be maintained meticulously in between molting seasons. Feathers are pure protein structures and are expensive to produce. A feather that has been pooped on can seriously reduce the flight ability.
Mobbing birds emit mobbing calls to recruit other individuals in the vicinity. Mobbing calls are different from alarm calls which alert others to the presence of predators. Alarm calls warn others to escape away while the mobbing calls facilitates grouping together to thwart a danger.
During the breeding season mobbing frequency increases. Playing recorded mobbing calls of chickadees brings roughly 50 species of birds and is used as a survey method.
Mobbing occurs in other species as well. There are squirrels that mob snakes, and African buffalo work together to mob lions. Some fish have even been observed mobbing turtles to protect their young. Meerkats mob snakes and foxes by poking, growling, and biting.
Mobbing also has a didactic component. Inexperienced young of the year can learn to recognize predators and how to deal with them as a group. Populations that are reintroduced into the wild sometimes fail because they lack knowledge about the identity of important predators. If you like bird behavior and natural history you can see a number of live webcams broadcasting from different bird nests including bald eagles.