In the Disney film Homeward Bound, two dogs and a cat undertake a perilous journey through the American wilderness to try and find their way home.
This story is the same but instead of pets, we have six giant snakes.
The Burmese python can grow up to 5.7 metres in length, making it one of the world’s largest snakes. As its name suggests, it hails from south-east Asia, but the exotic pet trade unleashed it upon the USA. Since 2000, these giants have spread across 1,000 square kilometres of Florida’s wetlands, suffocating local mammals and birds (and the odd alligator) along the way.
In 2006, Shannon Pittman from the University of Missouri-Columbia travelled to the Everglades National Park and implanted a dozen pythons with radio transmitters to track their movements. As part of that study, she put six of the snakes in sealed plastic containers, and drove them to locations 21 to 36 kilometres away before releasing them.
Pittman expected the snakes to randomly wander about their new environment. That is not what happened.
Instead, the pythons slithered home.
All of the them started moving towards the places where Pittman had originally captured them. Their accuracy was incredible. They stayed within 22 degrees of the right homeward bearing, and within 3 to 10 months, five of them had ended up within five kilometres of their original position.
This map shows their movements. Each colour represents a different snake. They were captured at the circles, taken to the triangles, and ended up at the diamonds. They all did spectacularly well. Even the blue snake seems to have headed in mostly the right direction before veering off for whatever reason.
Many animals, from pigeons to salmon to spiny lobsters, have incredible navigational skills, but this is the first time that any snake has demonstrated a similar acumen. They must have some sort of compass sense because they kept the right bearing, and they must have an internal map because they knew when they had reached the right destination.
For a compass, they could be picking up on the position of the sun or stars, the smell of home, or changes in the Earth’s magnetic field. As for the map, the snakes were always transported in sealed containers so they couldn’t memorise cues about their journeys as some animals do. They must be using some cues in their environment to work out their position but, again, we have no idea what those cues might be. (I would personally love it if they turned out to have a magnetic sense because I’ve written about such senses extensively—but really, who knows?)
Pittman suspects that this navigational prowess may have contributed to the Burmese python’s skill as an invader, allowing them to explore new terrain in confidence and expand their range more quickly. The discovery may also help scientists to better predict and control the snakes’ movements.
Reference: Pittman, Hart, Cherkiss, Snow, Fujisaki, Smith, Mazzott & Dorcas. 2014. Homing of invasive Burmese pythons in South Florida: evidence for a map and compass senses in snakes. Proc Roy Soc B http://dx.doi.org/10.1098/rsbl.2014.0040