Collective decision-making in aquatic mammals

Collective decision-making is an essential part of day-to-day life for group-living animals. These decisions can be unshared (e.g. leadership) or shared (e.g. consensus). Aquatic mammals face particular challenges when making collective decisions, including a three-dimensional habitat that can make group coordination and collective navigation a challenge. We systematically reviewed literature on decision-making in non-human mammals by examining the types of collective decisions observed and hypotheses used to structure analyses. Most of the current literature was centred around terrestrial species, particularly within primates and artiodactyls. There are no collective decision-making studies on aquatic mammal species outside of cetaceans. Both unshared and shared decision-making have been reported in whales and dolphins, with leadership found in killer whales Orcinus orca and bottlenose dolphins Tursiops sp. and consensus decisions in sperm whales Physeter macrocephalus. Five recommendations for decision-making research include: 1) clearly delineating the temporal components of decision-making, 2) standardising research to allow for comparisons, 3) considering both shared and unshared decision-making, 4) analysing decision-making across behavioural contexts, and 5) avoiding anthropomorphic terminology. Future studies of collective decision-making will help us better understand how non-human mammals overcome environmental and contextual challenges - particularly in the case of aquatic species such as cetaceans, which face challenges related to their aquatic environment and exhibit phenomena such as mass strandings.