Every day, millions of people watch their pet reptiles run, dig, swim or climb up against the walls of their enclosure. Reptile keepers call this “glass surfing,” but among scientists, this conduct is typically considered to be a type of repetitive behaviour, akin to pacing in polar bears.
Repetitive interactions with the barriers of a tank or cage might initially be endearing — because it seems like the reptile is eager to explore — but can quickly become distressing if a reptile simply does not stop. Many people feel helpless as they watch their beloved pet rub the scales on their nose off, causing ulcerations or deformities, or dig at the walls of an enclosure until streaks of blood are left behind.
Why do they do this, and how can we stop them?
Our lab examined the behaviour of one of the most popular pet reptiles around the world — the bearded dragon — and discovered some interesting similarities between repetitive behaviours in reptiles and mammals.
A common desire to escape
Mammalian carnivores, such as mink, polar bears and lions, sometimes perform repetitive pacing in captivity. And while there may be multiple reasons for the behaviour, researchers have found that thwarted escape is a common motivation.
(Unsplash/Mike Gattorna)
In other words, mammalian carnivores may pace when they want to escape, and anything that increases their motivation to escape might elicit pacing.
We wanted to find out whether the same is true for reptiles. Inspired by a study of the repetitive behaviours of caged mice from the 1990s, we examined exactly where lizards directed their repetitive behaviours within their homes. After all, if this behaviour represents a motivation to escape, then it should be biased towards escape routes.
Our results supported the common theory: Lizards climbed up, dug at or walked against the only “door” in their enclosure more than any other barriers. When this door was partially obscured, their behaviour became even more focused on the remaining transparent portion.
Pooping away from home
But this raises the question: What are reptiles trying to escape from?
(Unsplash/ Crissta Ames-Walle)
Enclosures that are too hot, small or boring may be a common cause of wanderlust. As a result, increasing the size or complexity of a reptile’s home can often reduce rubbing on enclosure barriers. However, there are also cases where this hasn’t worked, suggesting we don’t yet have the full picture.
Remarkably, in our study, we found that defecation was 15 times more likely to occur within periods when bearded dragons were performing repetitive barrier interactions. This suggests that — like rodents and other lizards — bearded dragons may prefer to do their business away from where they sleep and eat. Though whether defecation results in repetitive behaviours, or repetitive behaviours cause defecation, is still unclear.
Wild females roam in spring
We also found that female bearded dragons rubbed incessantly against enclosure barriers more in the spring compared to the winter and compared to males.
This may reflect how, during springtime, female lizards in the wild tend to roam widely whereas male lizards typically patrol a territory. Captive females could be more motivated to escape in the spring compared to captive males, who can still patrol the inside of their tank.
There were also some interesting things we didn’t find. For example, although repetitive pacing in mammalian carnivores often correlates with feeding, the same was not true for our lizards. This may be because, compared to mammalian carnivores, bearded dragons are much less active foragers. As adults, they are primarily vegetarians and may wait for insects to come to them. Therefore, feeding may not influence their motivation to escape.
Furthermore, although our lizards sometimes performed a lot of repetitive rubbing, digging or scrambling, they never got stuck performing those behaviours, as can happen for many other vertebrates. Whether this holds true for all reptiles may provide valuable insight into how repetitive behaviours change and develop over time.
(Unsplash/ John Dobbs)
Owners must observe and adapt
Our research shows that reptiles may sometimes scrabble against the walls of their enclosures for relatively benign reasons, like the need to poop.
It also shows how important it is to understand a species’ natural habitat and behaviour. For example, if female bearded dragons want to explore new areas in the spring, regularly moving the items inside the lizards’ home may simulate this exploration, reducing their need to escape.
Resolving repetitive behaviours in reptiles will not have a one-size-fits-all solution — decades of research have examined repetitive pacing in mammals, and these behaviours are still troublesome. The motivation behind a reptile’s behaviour could even differ day-to-day.
Caring for reptiles means that we must learn and observe with an open and curious mind, accept when we are wrong and adapt. Large and naturalistic enclosures will often improve a reptile’s welfare, but are not a one-time cure-all. As reptile keepers, we have the unique privilege of rising to this challenge.
