#Behaviour

Relationship between “naturalistic enclosures” and lizard welfare not so simple

/ gtattersall

Bearded dragons (Pogona vitticeps) have become one of the most popular pet reptiles and in many cases are contributing to research as well. But as their popularity has soared, so too has the need to better understand what these lizards actually need to live well in captivity. Our latest study, recently published in PLOS ONE, examines whether giving bearded dragons more “naturalistic” resources within their enclosures actually improves their well-being. These enclosures included features like climbing structures, loose substrate, and multiple hiding spots, compared to standard setups with only basic furnishings. We expected these more complex spaces to help the lizards behave more naturally and experience less stress. While the naturalistic enclosures did offer better thermal variety (important for ectothermic animals like reptiles), we were surprised to find that they did not have a clear effect on how active the lizards were, how they used their space, or how often they showed signs of stress or relaxation. 

Interestingly, only female lizards housed long-term in naturalistic enclosures showed lower levels of physiological stress (measured through ratios of white blood cells), suggesting that any benefits might be subtle or sex-specific. 

Overall, our findings show that simply adding complexity to an enclosure isn’t enough to guarantee better welfare. It may be that lizards don’t perceive naturalistic and standard enclosures as very different, or that enclosure size matters more than what’s in it. For reptile owners and researchers alike, the take-home message is this: meaningful welfare improvements require us to think beyond aesthetics or what human caretakers assume is “good” or “natural”—we need to constantly evaluate our efforts and ask the animals themselves what they think. 

The study is open access and available at the following link: https://doi.org/10.1371/journal.pone.0322682

Citation

Denommé, M and Tattersall, GJ. 2025. Influence of enclosure design on the behaviour and welfare of Pogona vitticeps. PLoS One 20(6): e0322682 https://doi.org/10.1371/journal.pone.0322682

A bearded dragon on top of cork bark. Photo credit Dr. Danilo Giacometti.

Dragons like to face the heat

/ gtattersall

At long last, my former MSc student, Ian Black’s first paper has been published!  (Citation below)  Ian graduated last year and moved to Ottawa, but has been maintaining contact and working with me to write his work up (so far, we have a book chapter in review and a second manuscript being edited now).

To many that keep lizards as pets, the results of this study might not be so surprising, as articulated by this meme:

 

From a scientific perspective, however, these results might not have been predicted.  So, what did we show? In a nutshell, we demonstrated that bearded dragons prefer to keep their heads facing toward the heat when given a choice.

To thermoregulatory biologists, this is intriguing.  Why? It is often stated in the herpetology literature that lizards are either heliothermic (i.e. they bask in the sun) or thigmothermic (i.e. they warm up via contact with the substrate), and an implicit corollary is that if a species is known to be heliothermic, it cannot respond to contact based thermal cues (i.e. they cannot sense heat via the skin).  Thus one might not expect them to orient toward or away from this kind of heat source or thermal gradient if they are heliothermic/baskers.

We conducted this study by creating an artificial thermal gradient to allow the lizards the chance to move and select different temperatures throughout the day.

Banner in gradient

Thermal image of a bearded dragon in a temperature gradient (~15C on left, ~42C on right) orienting toward the warm end.

Our paper clearly demonstrates that bearded dragons are very capable of orienting their body along a gradient of temperature, and thus are quite thermally “aware” of the environment around them.  We also demonstrate that both adults and neonates show this behaviour.  Finally, as the lizards choose warmer temperatures later in the day (i.e. move up the gradient), they orient less and less toward the heat, suggesting that they are capable of using their orientation to keep their heads from getting too warm.  Therefore, orientation behaviour is used to fine-tune their thermoregulatory control.  This is analogous to how Galapagos marine iguanas use sky-pointing orientation to maximise solar absorption int he early morning and maximise convective cooling later in the day to prevent overheating (Bartholomew, 1966. Copeia. p 241-250).

 

Please find links to the study below and consider sharing our findings.

Citation and Links

Black, IRG and Tattersall, GJ. 2017.  Thermoregulatory behavior and orientation preference in bearded dragons.  Journal of Thermal Biology. 69: 171-177. doi:doi:​10.​1016/​j.​jtherbio.​2017.​07.​009

For a limited time (until Sept 13, 2017) the paper is available for free for anyone that does not have a subscription here:

https://authors.elsevier.com/a/1VRVT15hXtsbUW

but I will provide permanent links to the pre-print version: Post Review Version or from the Brock University Respository.