Scientists watched lizards navigate a maze to learn more about how lizards use their senses to find food.
Introduction
Have you ever seen a lizard or snake flick their tongue in and out? Why do you think they do that? These animals have an extra organ at the top of their mouths that helps them smell! This organ is called the vomeronasal organ. When a lizard sticks out their tongue, the tip of the tongue picks up molecules from the air. When they pull their tongue back in, they press the tips of their tongue to the roof of their mouth. This special ability lets them notice a bigger range of scents than they can with just their noses.
The Guatemalan beaded lizard is one of the rarest animals in the world. Only about 600 of them live in the wild! They only live in one place: the thornscrub ecosystem of the Motagua Valley in Guatemala. They are one of the only venomous lizard species. We know some things about their diet, but not what strategy they use to find their food. What senses do they rely on most? Are they following a plan when they search, or is it just random? That’s what we wanted to find out!
Methods
We carried out a series of maze experiments using an 8-armed maze. Our test subjects were five Guatemalan beaded lizards from Zoo Atlanta: Harvey, Sluggo, Domino, Lucky, and Spot. Each experiment involved placing one of the lizards’ favorite foods (mice or raw scrambled chicken eggs) in the maze for them to find. Before we started, we spent some time observing their behavior. We watched for signs of stress, like breathing hard or scratching a lot at the walls. We let them explore the maze before the experiment started.
We did three experiments (see Figure 1).
We placed treats at the end of all 8 passages.
We blocked all but 3 passages to make a T shape, and placed treats in just one passage so that the lizards only had to choose whether to go right or left.
We used the same T-shaped maze as number 2, but first we dragged the treat along the passage to leave a scent trail.
During the experiments, we recorded the lizards’ movement through the maze with a video camera. We counted how many times they flicked their tongues per second. Lizards use the tongue to deliver scent to the vomeronasal organ. That’s why we used counts of tongue flicks to determine if they were using their vomeronasal organs to locate food. If they stopped looking for food for long enough, we stopped the experiment.
Results
Most of the lizards did all three experiments. During Experiment 1, Sluggo stopped looking for food and sat around for a long time. So, we decided not to include him in Experiments 2 and 3.
Experiment 1
Q: Can the lizards keep track of where they have already looked?
A: Usually! We found that the lizards sometimes revisited a spot, but they did better than they would have if they were picking directions at random.
Experiment 2
Q: Can the lizards smell the food from a distance?
A: Surprisingly, no! Most of our test subjects did the same as they would have if they had flipped a coin. We even tried putting bigger piles of treats in the maze and it didn’t seem to make a difference!
Experiment 3
Q: Can they follow a scent trail?
A: It certainly helps! They didn’t always get it right, but they did a lot better than a random choice (see Figure 2).
Discussion
We were surprised that the Guatemalan beaded lizards had a hard time following a scent without a scent trail. In the wild, they often eat things like eggs. Eggs can’t walk, so they can’t leave a scent trail! It might be that the lizards follow related scents, like smelling the droppings below birds’ nests. They could use those as a clue to find the nest.
We noticed that when they took longer to decide, they were more likely to choose correctly. We saw that they flicked their tongues more when they were in the passage with no treat at the end. As they got closer to the treats, they flicked their tongues less. This is most likely because as they moved further away from their treat, they had to put more effort into detecting its scent. Tongue flicking is a clue that the lizards are using vomerolfaction.
We combined what we learned from all three experiments. We think that these lizards use a strategy of first exploring to find scent trails, then carefully following those trails.
There’s a lot we still want to figure out. It’s hard to measure whether an animal is sniffing the air, because it isn’t as obvious as tongue flicking. In the wild, there are many other scents to choose from. So, maybe the strategies the lizards use for hunting depend on the kind of foods that are nearby.
Conclusion
When you are facing a challenge, it can be easy to decide that it is too hard and just give up. It can help a lot to think about a strategy and patiently work through your plan. Next time that you play a game of hide-and-seek, think about what strategy you are using to find your friends. You may find that you get better and better as you try out new ideas, or, like our lizards, combine strategies!
