Everything about Mobbing Behavior totally explained
In
behavioral ecology,
mobbing behavior is an
antipredator behavior which occurs when individuals of a certain species
mob a
predator by cooperatively attacking or harassing it, usually in order to protect their
offspring. A simple definition of mobbing is an assemblage of individuals around a potentially dangerous predator. Behavior includes flying about the intruder, dive bombing, loud squawking and
defecating on the predator. Costs of mobbing behavior include the risk of engaging with predators, as well as energy expended in the process.
Black-headed Gulls are one species which aggressively engages intruding predators, such as Carrion Crows. Classic experiments on this species by Hans Kruuk involved placing hen eggs at intervals from a
nesting colony, and recording the percentage of successful predation events as well as the probability of the crow being subjected to mobbing. The results showed decreasing mobbing with increased distance from the nest, which was correlated with increased predation success. Mobbing may function by reducing the predator's ability to locate nests, in other words as a distraction, since predators can't focus on locating eggs while they're under direct attack.
Adaptationist hypotheses regarding why an organism should engage in such risky behavior have been suggested by Eberhard Curio, including advertising their physical fitness and hence uncatchability (much like
stotting behavior in gazelles), distracting predators from finding their offspring,
warning their offspring, luring the predator away, allowing offspring to
learn to recognize the predator species, directly
injuring the predator or attracting a predator of the predator itself. The much lower frequency of attacks between nesting seasons suggests such behavior may have
evolved due to its
benefit for the mobber's young.
Niko Tinbergen argued that the mobbing was a source of
confusion to gull chick predators, distracting them from searching for prey . Indeed, an intruding carrion crow can only avoid incoming attacks by facing its attackers, which prevents it from locating its target. This is an example of an evolutionary pattern known as
divergent evolution.
Mobbing is thought to carry risks to roosting predators, including suffering harm from the mobbing birds or the risk of attracting larger, more dangerous predators. Birds at risk of mobbing such as
owls have adapted cryptic plumage and hidden roosting sites in order to reduce this danger.
In other animals
Another way the comparative method can be used here's by comparing gulls with distantly related organisms. This approach relies on the existence of
convergent evolution, where distantly related organisms evolve the same trait due to similar
selection pressures. As mentioned, many bird species such as the
swallows also show mobbing of predators, however even more distantly related species including
mammals are known to engage in this behavior. One example is
California Ground Squirrels, which are known to distract predators such as the
rattlesnake and
gopher snake from locating their nest
burrows by kicking sand into their eyes. This
social species also uses alarm calls.
Mobbing has also been observed in
fishes, for example
bluegills have been seen to attack
snapping turtles. Bluegills, which form large nesting colonies, were seen to attack both released and naturally occurring turtles, which may function to advertise their presence, drive the predator from the area, or aid in
cultural transmission of predator recognition.
Mobbing calls
Mobbing calls are
signals made by the mobbing species while harassing a predator. These differ from
alarm calls, which allow con-specifics to
escape from the predator. The
Great Tit, a European
songbird uses such a signal to call on nearby birds to harass a perched
bird of prey, such as an owl. This call occurs in the 4.5
kHz range, In the case of the alarm call, it's disadvantageous to the sender if the predator picks up on the signal, hence
selection has favored those birds able to hear and employ calls in this higher frequency range.
Mobbing calls may also be part of an animal's arsenal in harassing the predator - for example studies of
Phainopepla mobbing calls indicate it may serve to enhance the swooping attack on the predators, including
Scrub Jays. In this species the mobbing call is smoothly upsweeping, and is made when swooping down in an arc beside the predator. This call was also heard during agonistic interactions with conspecifics, and may serve additionally or alternatively as an alarm call to their mate.
Evolution
The evolution of mobbing behaviour is explained using
evolutionary stable strategies which are in turn based on
Game Theory.
Mobbing involves risks (costs) to the individual and benefits (payoffs) to the individual and others. The individuals themselves are often genetically related and it's increasingly studied with the
Gene-centered view of evolution by considering
inclusive fitness (the carrying on of one's genes through one's family members), rather than merely benefit to the individual.
By cooperating to successfully drive away predators all individuals involved increase their chances of survival and reproduction. An individual stands little chance against a larger predator, but when a large group is involved, the risk to each group member is minimized. By being in a large group, the risk for a particular individual is reduced or diluted. This so-called dilution effect proposed by
W. D. Hamilton is another way of explaining the benefits of cooperation by selfish individuals.
Lanchester's laws also provide an insight into the advantages of attacking in a large group rather than individually.
Another interpretation involves the use of the
handicap principle. Here the idea is that a mobbing bird, by apparently putting itself at risk, displays its status and health so as to be
preferred by potential partners.
Further Information
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