Collaborative Research: Geomagnetic Navigation by Weddell Seals Beneath Antarctic Ice

Abstract

The remarkable ability of many animals to navigate accurately over long distances has defied scientific explanation despite decades of research on species such as homing pigeons. Evidence that marine mammals use the Earth's magnetic field for navigation is less clear but numerous reports infer this sensory capability in a variety of marine mammals. Mistakes in this mechanism may be involved in mass strandings of whales and dolphins and a better understanding of marine mammal navigation ultimately may be useful in preventing or forecasting these events. Weddell seals precisely locate breathing holes in Antarctic sea ice after traveling hundreds of meters in darkness and a navigation mistake can result in death. In this project, the investigators will test a novel idea about marine mammal sub-ice navigation and orientation using geomagnetic fields by employing a custom-designed video and data recorder capable of monitoring fine-scale animal behaviors and movements when diving. The project will also further the NSF goals of making scientific discoveries available to the general public and of training new generations of scientists. The general public will be involved via web sites, a lecture series targeting underrepresented groups, and development of nationally disseminated K-12 teaching materials. A number of graduate and undergraduate students will be trained in the techniques of scientific discovery over the course of the project.

With limited oxygen stores during under-ice diving, Weddell seals are under strong selective pressure to navigate accurately and efficiently to locate breathing holes. The investigators hypothesize that geomagnetic navigation is both necessary and sufficient for Weddell seals to return to the vicinity of breathing holes. This project will be the first to rigorously field test geomagnetic navigation in a marine mammal as well as the first to measure the energetic cost of geomagnetic navigational behavior and evaluate how body oxygen stores and breath-hold duration influence spatial orientation and navigational strategies in a diving mammal. The investigators will measure changes in the behavioral and energetic responses of individual seals to different geomagnetic field properties and test those responses against precise predictions. By conducting tests during periods of high light intensity/long day length and low light intensity/reduced day length while simultaneously documenting sound sources and water currents, the experimental design provides a powerful technique for identifying a geomagnetic response as other sensory modalities are manipulated. These costs will be compared to those of other vertebrates to assess the evolutionary drivers for geomagnetic navigation. Demonstration of geomagnetic navigation in seals would also provide new insights into fine scale activities of other diving animals and the mechanisms that enable long distance migrations. Thus, the results have the potential to transform our understanding of navigation in all diving animals.