When a Duck Initiates Movement , Do Others Follow ? Testing Preference in Groups

Choice tests have been widely used to assess animal preferences. In the case of group-living species, these tests are commonly presented to animals in groups, because isolation can have strong effects on behaviour and motivation. However, assessing preference at the group level could be misleading if strong control of movement, through influential individuals, and group cohesion were present. The needs of majority of the population might not be properly represented by the test results. The current study investigated whether or not groups of ducks (four ducklings per group) have individuals that consistently initiate movement and considered the implications for group cohesion, synchronisation and a measure of preference during a choice test. In all groups included in the analyses, there were ducks that initiated more movements than the rest, and this trend was stronger when leading towards areas providing resources such as pools. Also, more ducks preferentially followed the first initiator (birds initiating most movements within a group) into the bathing area. Group cohesion was higher in groups that frequently had the same individual initiating movement. The number of followers following the ducks that initiated most movements was associated with the measure of preference (time spent at preferred area, as a proportion of total time spent at any area) but the number of movements initiated by these individuals was not. These results highlight the need to consider the effects of initiators and group-cohesive forces when conducting choice tests in groups of animals.