Saturday, January 31, 2015

Sensory Navigation

Reoccurring patterns of long-distance travel by migratory animals is a compelling mystery of sensory and behavioral biology.

US Fish & Wildlife Service
Salmon, sharks, elephant seals, and sea turtles traverse oceans swimming thousands of miles before returning to their natal home to breed.

Sea turtle hatchlings emerge from nests in soft coastal sand to begin their fateful trek to the ocean.

Avoiding predators, the waddling hatchlings wade into the ocean.

Beyond the roiling shore break, our intrepid new swimmers set a course toward the open sea. They establish and maintain their bearings long after the sight of land recedes in the distance.
How do turtles navigate with such exactitude?
Damien du Toit
Sea turtles like the loggerhead propel themselves over great expanses of ocean. Young loggerheads navigate more than 9,000 miles in the North Atlantic before returning to their origin.

Year after year, loggerheads follow reoccurring travel patterns seemingly without the aid of navigational reckoning over vast stretches of featureless water.

Following years in the open sea, juveniles find their way to familiar feeding grounds:
... juvenile turtles take up residence in coastal feeding grounds and show great fidelity to their feeding sites, homing back to specific locations after long migrations and experimental displacements. Similar navigational abilities exist in adult turtles, which migrate considerable distances between specific feeding areas and nesting beaches.
Lohmann Lab, University of North Carolina, Chapel Hill
Marine biologists postulate that sea turtles use Earth's magnetic field as a navigational aid. Two magnetic elements, inclination angle and intensity, vary across the globe creating geomagnetic signatures for geographic areas.

Lohmann, et al hypothesize that loggerhead hatchlings remember the signature of the magnetic field of their breeding ground then use this geomagnetic imprinting as a homing cue.

Brothers and Lohmann analyzed 19 years of loggerhead nesting data on Florida's east coast.
"We reasoned that if turtles use the magnetic field to find their natal beaches, then naturally occurring changes in the Earth's field might influence where turtles nest."
— J. Roger Brothers
Brothers and Lohmann found correlation between the locations of loggerhead nests over time and known shifts in the geomagnetic field.
"People have been on earth in our present form for only about 100,000 years, and in so many ways we’re still ironing out our kinks. These turtles we’ve been traveling with, they outrank us in longevity, having earned three more zeros than we. They’ve got one hundred million years of success on their resume, and they’ve learned something about how to survive in the world.
...What turtles could learn from us, I can’t quite imagine.”

― Carl Safina, Voyage of the Turtle