Do octopuses use projectiles in conspecific interactions? (#462)
Video data collected at a site at Jervis Bay, Australia, shows the apparently targeted throwing of debris during interactions between octopuses. This site has an unusually high density of Octopus tetricus, probably due to a local abundance of food and scarcity of dens. Along with mating, octopuses engage in a variety of interactions at this site, including a range of probing "reach" behaviors, displays, and occasional fights. Video collected over several years with divers mostly absent shows a number of cases where an octopus propels a clump of shells, algae, silt, and/or other debris towards another octopus nearby. Many of these are "direct hits" on the other octopus, whose behavior is apparently disrupted by the cloud of debris. The contexts in which the behavior is produced vary. In the majority of cases in which there is apparent targeting, a female octopus propels debris at a male octopus who has been probing or trying to mate with that female in the minutes before the debris is thrown. In other cases, the behavior is less clearly targeted on another octopus and, if targeted, its social role is unclear. Debris-throwing behaviors are also performed during den maintenance with no other octopus near the region where the debris is thrown. In order to establish targeting, it is necessary to exclude the hypothesis that cases where another octopus is hit by debris are accidental, perhaps due to a routine act of den-cleaning being performed in a context where a nearby octopus has the den-cleaner's attention. We discuss a range of observations that may discriminate the hypotheses of targeted and non-targeted throwing, including differences in the style of debris-removing behaviors seen in the presence and absence of another octopus. We also discuss the possibility that targeted throwing is an instrumentally conditioned learned behavior specific to a context of unusually high densities.