Noise helps understand group animal behaviour: IISc. paper

Researchers find that schooling of fish is noise-induced

Researchers often tend to filter out noise when studying animal behaviour in groups. However, a new study by the Indian Institute of Science, Bengaluru, finds that it may help them understand how complex group-level behaviours emerge from simple individual actions.

The study on cichlid fish (edible fish locally known askarimeen) movement finds that noise helps the understanding of group behaviour, such as swimming together in a synchronised manner to avoid predators and forage efficiently.

The paper, ‘Noise-induced schooling of fish’, was published in the journal Nature Physics. The researchers, who focussed on small to intermediate-sized groups, demonstrate that schooling — highly polarised and coherent motion — is noise-induced. “The fewer the fish, the greater the(multiplicative) noise and therefore the greater the likelihood of alignment,” the paper said.

Vishwesha Guttal, associate professor at the Centre for Ecological Sciences, IISc., and senior author of the paper, was quoted in an IISc. release terming the findings “counter-intuitive”, as we all usually think that noise reduces order.

The researchers tracked the cichlid fish swimming in large water tanks, studying both the direction in which the fish moved and the degree to which they were aligned towards each other. The researchers also tracked how these behaviours fluctuated over time.

“What we find is that when the fish are moving in a misaligned state, the fluctuations are actually high,” Danny Raj M., INSPIRE Faculty Fellow at the Department of Chemical Engineering, IISc., and a co-author on the paper, said in therelease.

The release also said when fluctuations were high, it had “surprising effects” on the behaviour of the group: they became more synchronised in their swimming because each member of the group was copying the direction of one of its neighbours, chosen randomly. “This is in contrast to classical models, which have suggested that each fish copied what the overall group was doing on average,” the release said.

“When they are ordered, copying the direction of a random individual from the group doesn’t change the overall behaviour very much. When they are highly disordered, this copying has a greater effect,” Prof. Guttal said.

When the fish are not well aligned with group members, the noise resulting from the fluctuation grows larger, eventually ‘kicking’ the group from one state (random swimming) to a different state (schooling), the release said.

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