The information centre hypothesis (ICH) is a theory that states bird species live in communal roosts primarily for the advantage of gaining information from others in the community regarding the location of unevenly distributed food resources. This hypothesis was first proposed by Peter Ward and Israeli biologist Amotz Zahavi (1973). They stated that birds join assemblages in order to gain information about food resources and increase foraging efficiency. Using this strategy would allow unsuccessful birds to return to the population and gain information, often by observing behavioural differences in successful birds. Following the exchange of knowledge, the unsuccessful individuals then follow those deemed successful back to the resource location. The hypothesis has been studied and experimentally supported in many different types of communally roosting birds, notably crows and vultures. This strategy is regarded as evolutionarily adaptive, because it would prevent the unsuccessful bird from having to start the search for food over in a random method. By the early 1980s, the information centre hypothesis was widely accepted and used to explain communal roosting behaviour, however this popularity also led to substantial criticism. One criticism of the theory is the multiple assumptions required to fulfill the criteria to support the hypothesis. Another criticism of the theory is its narrow scope, as it pertains strictly to food information sharing. Additional criticism questions whether the information centre hypothesis is an evolutionarily stable strategy.
Theory The information centre hypothesis was first described by Peter Ward and Amotz Zahavi in 1973. They theorized that communal roosts evolved and were maintained as a result of the advantage obtained by unsuccessful individuals in locating food resources from information provided by successful individuals. The information centre hypothesis requires that two conditions be met; first, that successful individuals return to the communal roost after feeding, and second, birds without the knowledge of the food source must recognize these individuals as successful and then follow them back to the food source. In their primary work, Ward and Zahavi studied red-billed quelea and cattle egret birds, noting that individuals who were unsuccessful in the morning would return to the communal roost and follow other birds away from the roost in the afternoon. Mock et al. (1988) provide seven requirements which must be fulfilled in a species for the information centre hypothesis to be supported. First, birds who are successful in foraging must return to rewarding locations. Second, while some individuals discover these rewarding locations, others remain unaware of these locations. Third, previously unsuccessful individuals must be able to recognize others as successful or unsuccessful. Fourth, unsuccessful individuals must leave the communal roost when the successful individuals leave the roost. Fifth, the previously unsuccessful individuals must follow the successful individuals to the feeding location. Sixth, previously unsuccessful individuals must be permitted to share the food source by successful individuals. Seventh, the overall net benefit of receiving information and following, must be greater than an individual searching for food on their own. While it may seem counterproductive for a successful individual to share resource knowledge, the information centre hypothesis argues that this behaviour is adaptive. The information centre hypothesis argues this behaviour is a defensive mechanism so that in the event of a sudden resource devaluation which destroys the food source, the bird would be able to obtain new resource information from other roosting individuals. This idea has been supported in studies which show that individuals in areas with a recent heavy snowfall searched longer for a communal roost compared to individuals in non-snowy areas. This is potentially so the bird would be able to upgrade their resource knowledge with others' information. Support for the information centre hypothesis includes the idea that individuals living in groups have more resource information available, at a lower cost than finding it themselves. In addition, multiple studies have made note that food sources for flock-living birds are typically consumed quickly by other predators, such as mammals or decomposers. Therefore, individuals likely do not suffer from sharing knowledge with conspecifics due to the short-lived nature of the resource. Currently, there is only speculation as to how the information is conveyed. It has been suggested that the successful members first convey their knowledge through displays and the unsuccessful members then follow, or that the unsuccessful members circle in the air or slowly fly out and proceed to join the successful members when they take off. Ward and Zahavi approached the explanation for the ICH in several different ways, but each explanation is related to the ability to distribute knowledge of resources. In this case, roosting can be divided into several components: advertisement, synchronized breeding, seasonality, mood, and predation.
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