"Homing" Crocs Voyage Hundreds of Miles

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"Then all of a sudden it seemed to decide to return home.

"We don't know whether or not it used those several months to [orient itself]—to get clues and later use them to return home. But on the fourth of December it just made a beeline [for home] and moved 249 miles [400 kilometers] in 20 days.

"We say that it headed home for Christmas."

Reptiles on the Move

The study was not the first to document crocodiles' ability to travel great distances on their way back to their original habitat. (Related news: "Costa Rica's "Problem Crocs" Return After Removal" [September 26, 2003].)

However, most other studies have relied on radiotelemetry, a difficult technique for studying animals that live in remote locations, have huge geographic ranges, and are easily disturbed by human presence, the study authors wrote.

Satellite tracking allows data to be accessed continuously from the crocodiles without human interference, giving scientists a clearer picture of their habits.

Crocodiles are thought to live mostly within their home rivers, but scientists say not enough data exist to be sure.

"More studies may show that large animals go out of river systems naturally," Franklin said. "It's clear that they can undertake rather large voyages."

To Franklin's knowledge, the new study represented the first time satellite tracking was used to study the movements of wild crocs.

The technology allows researchers to continually gather movement data without disturbing the unpredictable animals or influencing their behavior.

Bird Cues?

No one knows how crocodiles are able to navigate.

"We can probably look to some of the well-known mechanisms of other organisms as a place to start," said Perran Ross, a crocodile biologist at the University of Florida (UF) who was not involved in the study.

"Whether crocodiles are different would be interesting to see."

Notable navigators in the animal world use visual cues such as the sun's position, familiar landmarks, a keen sense of smell, and the Earth's magnetic fields.

Pigeons, probably the best studied animal navigators, appear to rely on several methods, the first of which is recognizing landmarks.

After many years of flying around, pigeons know their way—much like humans can drive around their hometowns without using street signs.

"Crocodiles are long-lived and active," UF's Ross explained. "It's quite conceivable that over a 30-year lifetime, a crocodile would know a very large area around it. We know that they have the ability to learn."

Birds, lobsters, sharks, and other animals may also find their way by following the Earth's magnetic field. (Related news: "Lobsters Navigate by Magnetism, Study Says" [January 6, 2003].)

Whatever methods crocodiles use, their homing ability may highlight their distant relation to birds.

"Crocs are actually more closely related to birds than they are to all other reptiles," study lead author Franklin said.

"So ... they might be using similar cues to navigate."

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