Kenneth J. Lohmann, Ph.D. - US grants

NONTECHNICAL SUMMARY Lohmann, K., IBN 94-19993 Mechanisms of Orientation and Navigation Sea turtle hatchlings begin an amazing long-distance migration as soon as they emerge from their underground nests on oceanic beaches. They scramble to the sea and swim through the surf, then quickly establish a course towards the open ocean, Maintaining their direction after swimming beyond sight of land.. Little is known about how hatchling sea turtles maintain their course through a vast ocean that contains no obvious landmarks. Near the beach, wave direction provides a reliable cue, Which the hatchlings seem to use initially. But farther from land, where waves no longer reliably indicate direction, the hatchlings appear to depend on the magnetic field of the earth. Recent experiments have demonstrated that sea turtles have a well- developed magnetic compass that allows them to maintain a specific heading, even in total darkness. For long-distance migrants such as sea turtles, the geomagnetic field not only provides a possible cue for compass orientation, but a potential source for worldwide positional information. Several parameters of the earth s magnetic field vary predictably with latitude and it appears that hatchling sea turtles can sense these parameters. The research that Dr. Lohmann will carry out is designed to investigate: (1) how hatchlings may use these geomagnetic parameters in global position finding; (2) how young sea turtles may acquire a directional preference and how the preference influences orientation; and (3) the mechanism hatchlings use to detect wave direction and how this information interacts with the information from the magnetic compass. All species of sea turtles are now either threatened or endangered. Thus this research will provide information useful to conservation workers trying to save these animals from extinction. In addition it will provide valuable information about how animals (including turtles, fis h and whales) navigate using information from the magnetic field of the earth. .

Animal Behavior Program
Nontechnical Abstract


Proposal #: 9816065
PI: Lohmann, Kenneth
Title: MAGNETIC POSITION-FINDING AND NAVIGATION IN SEA TURTLES

How sea turtles navigate across vast expanses of seemingly featureless ocean has remained a mystery for decades. Recent experiments have revealed that hatchling loggerhead turtles can sense two different features of the earth's magnetic field that may provide information on global position. These results suggest that the key to the sea turtle navigational system may be an ability to determine location using magnetic field features. The proposed research has three major objectives. The first is to investigate how hatchling loggerheads respond to magnetic features marking various locations throughout the North Atlantic. A second is to examine whether turtles can distinguish between the magnetic features that mark different coastal regions that are contiguous and relatively close together, as adults would presumably need to do if they use magnetic features to navigate into the vicinity of their natal beaches. A final set of experiments investigates what specific feature or features of the earth's field the turtles detect and respond to.

Results of the research are likely to reveal previously undiscovered mechanisms of position-finding and navigation that are used not only by sea turtles, but by diverse animals such as migratory birds, commercially important fishes (e.g., salmon), and marine mammals. In addition, understanding how sea turtles navigate, and how they find their natal regions as adults, may benefit conservation efforts to save these threatened and endangered species from extinction. Results may also reveal new navigational methods relevant to human guidance systems.

GEOMAGNETIC GUIDANCE MECHANISMS IN SEA TURTLES

PI: Kenneth J. Lohmann
Co-PI: Catherine M. F. Lohmann

The long-distance migrations of sea turtles involve some of the most extraordinary feats of orientation and navigation in the animal kingdom. Hatchling turtles entering the ocean for the first time immediately establish courses toward the open sea and steadfastly maintain them long after swimming beyond sight of land. As the turtles mature, they often follow complex migratory pathways across vast distances that sometimes span entire ocean basins. Older turtles take up residence in feeding grounds but periodically migrate long distances to particular mating and nesting sites, after which many navigate back to the same feeding sites that they inhabited previously. How sea turtles guide themselves across vast expanses of seemingly featureless ocean has remained an enduring mystery of animal behavior.
Although sea turtles, like other animals, exploit multiple cues in orientation and navigation, growing evidence suggests that the Earth's magnetic field provides turtles with an important source of both directional and positional information that can be used in different ways at different life history stages. As hatchlings, turtles may first use the Earth's field as a directional cue that enables them to maintain headings as they migrate out to sea. Later, in the open ocean, regional magnetic fields apparently function as navigational markers that elicit changes in swimming direction at crucial geographic boundaries, thus helping young turtles remain within favorable oceanic regions and progress along the migratory route. Turtles at this life history stage, however, do not navigate to specific geographic locations. In contrast, older juveniles take up residence in coastal feeding grounds, and recent evidence suggests that they acquire a "magnetic map" that enables them to navigate to specific feeding sites. A similar navigational ability may explain how adult turtles locate nesting beaches.
The proposed research consists of field and laboratory experiments designed to investigate the role that magnetic cues play in guiding sea turtles at several different stages of their lives. The work has three major objectives. First, the researchers will conduct a pivotal field test to determine whether hatchling turtles that have migrated a few kilometers away from their natal beaches in Florida rely on magnetic compass orientation to maintain offshore headings, as has been hypothesized on the basis of extensive laboratory results. Second, the researchers will investigate how young loggerheads exploit regional magnetic fields as open-sea navigational markers during their trans-oceanic migration. Finally, the newly discovered magnetic map sense of juvenile green turtles will be studied with a view toward determining how turtles exploit magnetic fields to navigate to coastal locations used as feeding sites. An improved understanding of how sea turtles guide themselves during transoceanic migrations, and how they recognize and relocate specific geographic locations of importance to them, will benefit conservation efforts to save these jeopardized species from extinction. In addition, the results of the work may provide insights into possible new methodologies relevant to human navigation. The project will provide research experience for a number of undergraduate and graduate students.

ABSTRACT NOT PROVIDED

The long-distance migrations of sea turtles involve some of the most extraordinary feats of orientation and navigation in the animal kingdom. Hatchling turtles entering the ocean for the first time immediately establish courses toward the open sea and steadfastly maintain them long after swimming beyond sight of land. As the turtles mature, they often follow complex migratory pathways that span entire ocean basins. Older turtles take up residence in feeding grounds but regularly migrate long distances to particular mating and nesting sites, after which many navigate back to the same feeding sites that they inhabited previously. How sea turtles guide themselves across vast expanses of seemingly featureless ocean has remained an enduring mystery of animal behavior.
Growing evidence suggests that the Earth's magnetic field provides turtles with an important source of both directional and positional information that can be used in different ways at different times in their lives. As hatchlings, turtles may first use the Earth's field as a directional cue that enables them to maintain headings as they migrate out to sea. Later, in the open ocean, regional magnetic fields apparently function as navigational markers that elicit changes in swimming direction at crucial geographic boundaries, thus helping young turtles remain within favorable oceanic regions and progress along the migratory route. Turtles of this age, however, do not navigate to specific locations. In contrast, older juvenile turtles take up residence in coastal feeding grounds, and recent evidence indicates that they acquire a ?magnetic map? that enables them to navigate to specific feeding sites. A similar navigational ability may explain how adult turtles locate nesting beaches.
The proposed research is designed to investigate the role that magnetic cues play in guiding the migrations of sea turtles. The researchers will investigate how young loggerheads exploit regional magnetic fields as open-sea navigational markers during their first transoceanic migration. In addition, the researchers will study the newly discovered magnetic map sense of juvenile turtles to gain insight into how turtles use magnetic fields to navigate to specific feeding sites and to determine how the map is organized. An improved understanding of how sea turtles guide themselves during transoceanic migrations, and learn to find specific geographic locations, will benefit conservation efforts to save these jeopardized species from extinction. In addition, the results of the work may provide insights into new methodologies relevant to human navigation. The project will provide research experience for a number of undergraduate and graduate students.

The long-distance migrations of sea turtles involve some of the most extraordinary feats of navigation in the animal kingdom. Newly hatched turtles follow complex migratory pathways that span entire ocean basins. Older turtles regularly travel between feeding areas and nesting sites that can be more than a thousand miles apart. This study uses behavioral experiments to investigate the mystery of how sea turtles guide themselves across vast expanses of seemingly featureless ocean.

Growing evidence indicates that a sea turtle's navigational prowess depends in part on a sophisticated ability to perceive the Earth's magnetic field. Turtles are evidently able to detect the very slight differences in the Earth's magnetic field that exist in different geographic areas. One set of experiments investigates how young turtles use these differences as navigational markers during their first migration. Another set of experiments focuses on how older turtles learn the magnetic topography of the areas where they live and develop 'magnetic maps', which help them to navigate to specific destinations.
An improved understanding of how sea turtles guide themselves during transoceanic migrations will benefit conservation efforts to save these jeopardized species - and other ocean migrants - from extinction. In addition, the results of the work may provide insights into new guidance strategies that can be adapted to human navigation. Finally, the work attracts the interest of many undergraduate and graduate students and thus provides an excellent mechanism for teaching principles of scientific research, as well as giving students direct, hands-on experience with species of special concern.

The ability of animals to guide themselves unerringly during long-distance migrations has inspired both awe and envy in humans, who only recently, through global positioning technology, managed to equal the skills of elite animal navigators such as loggerhead sea turtles. These turtles leave their home beaches as hatchlings and migrate across entire ocean basins before returning years later to nest in the same coastal area where they originated. How adult turtles navigate to their natal beaches has remained enigmatic, but accumulating evidence suggests that turtles imprint on the unique geomagnetic signature of their natal beach and then use this information to return. The research will investigate the geomagnetic imprinting hypothesis using a multidisciplinary approach. Results will assist efforts to conserve animals such as sea turtles that undergo natal homing. For example, attempts to reintroduce sea turtles to geographic areas where they once nested have been largely unsuccessful because young turtles released in such areas seldom return as adults. An improved understanding of how turtles find their home beaches may help save these jeopardized species from extinction. Findings are also likely to reveal new modes of navigation that can be adapted for guidance systems of humans and autonomous vehicles. Broader impacts include providing research experience for undergraduate and graduate students, broadcasting findings into K12 classrooms through the North Carolina Museum of Natural History, and creating instructional web modules for K12 education, thereby enhancing both science education and public awareness of endangered sea turtles.

The long-term objective of the research is to determine the behavioral and sensory mechanisms that underlie natal homing in sea turtles and other long-distance marine migrants. The research will test several central predictions of the geomagnetic imprinting hypothesis: (1) behavioral experiments will investigate whether nesting adult female turtles locate their natal beaches using the unique magnetic signature of their natal area; (2) statistical analyses will be used to determine whether the spatial distribution of turtle nests along continental coastlines is affected by fluctuations in Earth's magnetic field, as the geomagnetic imprinting hypothesis predicts; and (3) magnetic orientation behavior of turtle embryos prior to hatching will be studied to determine if imprinting might occur during development. Results and data will be disseminated primarily in scientific journals; when possible, appropriate data and metadata files will be posted in online supplementary materials or with services such as Dryad, which many journals now support.