Friday, November 5, 2010

Surfing Crocs

According to a study started by Steve Irwin and finished by researchers at the University of Queensland, salt water crocodiles body surf from island to island. The article states: “Despite being found on several islands across this range, different crocodile groups haven't evolved into completely unique species—the way Darwin's finches evolved on the Gal├ípagos Islands.” Therefore something must be happening in order to keep the gene pool mixed. These researches suggest it is because the crocodiles are hopping from island to island. But how? Crocodiles are excellent swimmers, but typically would not have the endurance to make it from island to island. The researchers tested their hypothesis that the saltwater crocodiles body surf on the tides.

The experiment was set up by tagging 27 crocodiles with acoustic transmitters, and then monitoring their movements through the rivers. They also were fitted with sensors that recorded water depth and temperature. The data was recorded for a year and then analyzed. It was found that crocodiles that were taking journeys of 10Km or more would wait and ride the tide out, riding on the surface currents. If the tides changed favor, the crocodiles would swim and rest on riverbeds or river banks. The crocodiles waited for the tides for every journey that was over 10Km. The longest journey was found to be 25 days and 590Km.

Currently the exact reason for travelling such distances is unknown. There doesn’t seem to be a pattern in their travels, so it isn’t thought to be migratory. These researchers suggest it is for food or mating, although they have no specific evidence on the matter. The fact that the crocodiles do not swim in a straight line on their long journey suggests they must have exceptional navigational instincts. Because they wait for the tides to go out, this suggests they have a specific destination in mind before they leave. One researcher states: “With a crocodile, they have to navigate all these features”—surfing from rivers to deltas and across the open ocean to various islands—“to get from A to B. It's not in a straight line, so they must have a very sophisticated navigational ability.”

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  1. Wow, a 25-day journey??? It is amazing how these crocodiles have changed their behavior to match the tides and currents to help them get where they need to go. Figuring all that out to do it right must have been quite the trial-and-error process, because I doubt they are born with that knowledge.

  2. I had just prepared my post using the same topic! Bummer! It is amazing that they are capable of traveling with the currents for so long and their avoidance techniques for avoiding unfavorable currents is very cool.

  3. Wow this is really interesting. I hadn't really thought about crocodiles making such a long journey. It is really neat that they have figured out a way to save some energy and still get to a different Island. I wonder why they choose to go so far. How do they "know" where they are headed?

  4. Vertebrates use all kinds of interesting tools for navigation - sensing the earths magnetic field, seeing polarized light, smell. I don't think this has been studied in crocodiles.

  5. This is a very interesting post. I'm with Rachael, I never thought about crocodiles traveling such far distances. It would be very interesting to see what the different mechanisms are that crocs use to navigate to different islands and how they know where they are going.