Slippery snakes sneaking up trees
Guam is a small island in the Western Pacific ocean whose native bird population has been decimated by invasive brown tree snakes accidentally introduced in the 1940s and 50s. The snakes readily climb the island’s trees to feast from birds’ nests. One particularly hard-hit victim is the Micronesian starling. Scientists have been trying to protect the birds by putting nesting boxes high up on poles which are surrounded by smooth baffles, like metal covers, to stop the snakes climbing up. But, as it turns out, these snakes are slippery customers, as Eva Higginbotham heard this week from Colorado State University’s Julie Savidge…
Julie - We had an outdoor arena where we would put maybe two to four snakes in during the night, this is a nocturnal snake and then we had cameras that would record their activity. Snakes couldn't defeat the baffle, but then all of a sudden, one of the snakes wrapped its body around the metal cylinder. This is an eight inch metal cylinder and formed a loop and then wiggled its way upwards.
Eva - You've actually sent me some videos of this. Honestly, it looks sort of like a cartoon. It doesn't look like a snake should be able to do this. Were you surprised when you saw this?
Julie - Oh, we were absolutely amazed. Tom, my colleague on the paper said that he watched the video probably a dozen times. He then sent it to me. I wasn't able to be on island at the time and I had never seen a snake doing anything like this. So yes, it appeared we are seeing a very unique form of movement. The snake first forms a loop around the cylinder with its body, and it creates a knot or some sort of interlocking region with the tail part of its body, and the anterior part of the body towards the head. And this loop - lasso, which we're calling it - squeezes the cylinder to generate friction and prevent the snake from slipping down this smooth surface. The snake has little bends of its body within the loop of the lasso, which it can then move upward, and it kind of looks like a wave moving along the body; and it gradually shifts these bends upward.
Eva - How many snakes did you see climb up the pole this way? Was this just a one hit wonder super snake, or do you think this is something this species can do in general?
Julie - We think this species can do it in general. For our studies we had a total of 15 snakes - that we had tested - that actually showed this type of locomotion, but undoubtedly more can do this as well. Brown tree snakes evolved in tropical regions where there are smooth barked trees, and it's possible that this form of locomotion helped them scale these sorts of trees and get to resources in those trees.
Eva - So now you've seen that these snakes can climb up to get to the birds this way - what's next?
Julie - Understanding this lasso locomotion, we can predict circular structures that brown tree snakes couldn't readily climb. So we know now that placing nest boxes for Micronesian starlings on relatively narrow utility poles is not such a smart idea. Placing them on larger diameter poles would probably be safe. We can also develop other baffles that we think brown tree snakes would have a much more difficult time using lasso locomotion on; for instance, my colleague and I developed an ice cream shaped cone where it's narrower at the bottom and wider at the top, and that makes the snakes have to adjust that loop that lasts as they climb, and that's pretty difficult for them.