Nearest-neighbour clusters as a novel technique for assessing group associations

2023

Ecology and Evolution

Self Cite

Most animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviors like active scanning or head lifting are usually used to quantify vigilance but may not be accurate measures of this. We suggest that measuring an animal's blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We describe an observational study of a captive population of red deer, where we measured the blinking rates of individual deer from groups of differing sizes (where mean group size ranged between 1 and 42.7 individuals). We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors.

Section: Methodsmentioning

confidence: 99%

Red deerCervus elaphusblink more in larger groups

Rowe

Robins

2023

Ecology and Evolution

Self Cite

“…The distance of five body-lengths was chosen following pilot testing, and was used because estimating individual separations beyond this length was logistically difficult for distant gulls. Choosing an arbitrary cut-off like this can have implications for generating larger association matrices 26 , but was sufficient for the simple relationships we consider here. Having identified a group, two observers waited at a maximum of 30 m from the birds for five minutes, to allow for habituation.…”

Section: Methodsmentioning

confidence: 99%

Black-headed gulls synchronise their activity with their nearest neighbours

Evans

Lihou

2018

Sci Rep

Self Cite

Animals in groups can benefit from synchronising their behaviour, where multiple individuals conduct similar activities at the same moment in time. Previous studies have demonstrated that some species show synchronisation of vigilance behaviour, but have not explored the mechanism driving this behaviour. Synchronisation could be driven by animals copying their closest neighbours, which would mean that close proximity should lead to increased synchronisation. We simultaneously observed the behaviour of multiple individual black-headed gulls (Chroicocephalus ridibundus) within resting groups, and compared the activity of a focal individual with its two closest neighbours and a randomly selected control individual. Focal individuals were more likely to be synchronised with their closest neighbour. Synchronisation became less likely if individuals were not the closest neighbour. This suggests that synchronisation seen within groups is dependent upon the spatial positions of its members, and black-headed gulls pay more attention to their closest neighbours.

“…A blink was defined as a rapid full closure of the eye. Group size was arbitrarily defined as the number of individuals aggregated no more than five body lengths away from at least one member of the group containing the focal deer, meaning a measured group was composed of individuals associated by a chain rule of association (see [37] for discussion of defining groups by associated neighbours within arbitrary distances). Before starting any set of observations, the observers waited 10 minutes at the site to habituate the deer.…”

Section: Methodsmentioning

confidence: 99%

Red deerCervus elaphusblink more in larger groups

Rowe

Robins

2020

Preprint

Self Cite

Most animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviours like active scanning or head lifting are usually used to quantify vigilance, but may not be accurate measures as the individual could be conducting them for other purposes. We suggest that measuring an animal’s blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure, and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors.