A note on overdispersion as an index of behavioural synchrony: a pilot study in dairy cows

Abstract

We developed a method for studying the synchrony of behaviour based on calculations of overdispersion of a binomial process. The lying behaviour of cows was investigated under two different housing units inside the same barn. The first unit housed 30 cows undergoing conventional milking and the second unit housed 27 cows undergoing automatic milking. The lying behaviour of the cows was observed over 3 weeks in 12 periods of 6 h each. Every 5 min, we counted the number of cows lying down in the cubicles. As external cues, like feeding and conventional milking, can promote synchrony in dairy cows, we expected that cows conventionally milked would show more behavioural synchrony than automatically milked cows. Cows lied down synchronously in both units (overdispersion 1.67, P , 0.01). Lying synchrony tended to be slightly bigger in automatically than in conventionally milked cows (overdispersion 1.76 v. 1.58, P 5 0.09), although the proportion of cows lying down was on average greater in conventionally than in automatically milked cows (60.7% v. 45.6%). This suggests that synchronized lying behaviour in cows is a constant phenomenon that depends on social facilitation rather than on external cues. The overdispersion index appears to be a useful tool for studying the synchrony of animal behaviour when observations are made at the group level.

Black-headed gulls synchronise their activity with their nearest neighbours

“…We could attempt to pick apart these mechanisms by tracking the spread of a behaviour within the group using continuous sampling techniques, and we could record the spatial position and orientation of individuals along with their proximity of potentially influencing environmental factors. However, without intentional experimental manipulation, it is unclear whether there are predictable differences that separate the possible mechanisms causing the synchronisation behaviour that we observed, and we call for more sophisticated experiments and analytical techniques (such as those described in 44 – 49 ) that would allow us to tease apart the mechanisms causing spatial synchronisation in groups. Any experimental manipulation of either wild resting groups or their environment is not a trivial task: the effects of social composition could be investigated using managed groups where individuals are identifiable and can be removed, whilst the effects of perceived predation risk and disturbance could be investigated by manipulating cover or cues that indicate predator presence.…”

Ontogenetic shift from aposematism and gregariousness to crypsis in a Romaleid grasshopper

“…Aggregation: Active aggregation of nymphs was evaluated as synchronization of movement by testing for overdispersion relative to a binomial process [ 48 ]. For each replicate observation, the frequency distribution of the number of nymphs engaged in moving was compared with a binomial distribution around the mean number of moving individuals over the course of that observation.…”