Movement Behavior of Manatees and Dugongs: II. Small-Scale Movements Reflect Adaptations to Dynamic Aquatic Environments

The coastal marine and inland freshwater environments inhabited by manatees and dugongs around the world are spatially heterogeneous and highly dynamic over a range of time scales, often aligned with predictable geophysical cycles (tidal, diel, seasonal). Central to sirenian adaptations for meeting these varied ecological challenges is plasticity in their movement behavior , which allows them to find and utilize resources that are key to their survival and reproduction, to escape risks posed by predators and humans, and to leave habitats that become inhospitable. The development and deployment of animal-borne GPS tags have tremendously advanced our knowledge in the domain of small spatio-temporal scales by providing highly accurate locations many times per day. The recent addition of multi-sensor biologgers is further deepening our understanding of the connections between fine-scale behavioral changes and environmental features experienced by the animal. Individual sirenians generally show strong site fidelity within a season to one or a small number of high-use core areas within their home range. Manatees and dugongs usually move at a leisurely pace within and between habitats that provide forage, shelter, thermal refuge, and (for coastal manatees) fresh water. As marathon swimmers, sirenians can sustain a cruising speed of ~2 to 4 km/h for lengthy periods, but when threatened, they can briefly sprint at speeds up to 30 km/h. A common theme across species, ecosystems, and spatio-temporal scales is that access to forage is often constrained due to environmental fluctuations, including tidal cycles in coastal systems, seasonal water level cycles in flood-pulse river systems, and seasonal temperature changes in higher-latitude regions. Sirenians negotiate trade-offs among key activities within these fluctuating environments while apparently minimizing exposure to predators and other threats through their movement behavior . There is an increasing body of evidence suggesting that many sirenian populations predominantly forage at night, plausibly as an adaptation to reduce risk of falling victim to hunters or, possibly, boat strikes. Sexual selection has also shaped the behavioral ecology of sirenian movements, as mature males are frequently on the move in search of estrous females during the breeding season . Mating and parturition can alter female movements and habitat selection for brief periods, but otherwise reproductive status does not appear to strongly affect female movement behavior over large or small scales. Further research is warranted on most sirenian populations to confirm these conclusions. Continued technological and analytical advancements promise to reveal more secrets of these fascinating and cryptic creatures.