Why do dolphins carry sponges?

• Published in: PloS one 2008-12, Vol.3 (12), p.e3868-e3868
• Main Authors: Mann, Janet, Sargeant, Brooke L, Watson-Capps, Jana J, Gibson, Quincy A, Heithaus, Michael R, Connor, Richard C, Patterson, Eric
• Format: Article
• Language: English
• Subjects: Animal behavior; Animal cognition; Animal reproduction; Animals; Aquatic mammals; Australia; Biology; Bottle-Nosed Dolphin - physiology; Cetacea; Cognition; Comparative analysis; Cost benefit analysis; Costs; Deep water; Disease transmission; Diving - physiology; Dolphins; Dolphins & porpoises; Dolphins (Mammals); Ecology; Ecology/Behavioral Ecology; Ecosystem; Evolutionary Biology/Animal Behavior; Evolutionary Biology/Evolutionary Ecology; Feeding Behavior - physiology; Female; Females; Foraging habitats; Generalized linear models; Habitats; Innovations; Learning; Male; Marine mammals; Memory; Ontogeny; Parapercis clathrata; Population; Porifera - physiology; Social aspects; Social behavior; Social discrimination learning; Social factors; Social interactions; Specialization; Sponges; Success; Time allocation; Tool use; Tursiops; Tursiops truncatus; Wild animals
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0003868

Tool use is rare in wild animals, but of widespread interest because of its relationship to animal cognition, social learning and culture. Despite such attention, quantifying the costs and benefits of tool use has been difficult, largely because if tool use occurs, all population members typically exhibit the behavior. In Shark Bay, Australia, only a subset of the bottlenose dolphin population uses marine sponges as tools, providing an opportunity to assess both proximate and ultimate costs and benefits and document patterns of transmission. We compared sponge-carrying (sponger) females to non-sponge-carrying (non-sponger) females and show that spongers were more solitary, spent more time in deep water channel habitats, dived for longer durations, and devoted more time to foraging than non-spongers; and, even with these potential proximate costs, calving success of sponger females was not significantly different from non-spongers. We also show a clear female-bias in the ontogeny of sponging. With a solitary lifestyle, specialization, and high foraging demands, spongers used tools more than any non-human animal. We suggest that the ecological, social, and developmental mechanisms involved likely (1) help explain the high intrapopulation variation in female behaviour, (2) indicate tradeoffs (e.g., time allocation) between ecological and social factors and, (3) constrain the spread of this innovation to primarily vertical transmission.