#Lizard

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.

Unlocking the Motivations of Repetitive Behaviours in Reptiles

/ gtattersall

Our latest study (https://doi.org/10.1016/j.applanim.2024.106484) sheds light on a perplexing behaviour seen in captive reptiles, namely their interactions with barriers (IWB), a form of repetitive behaviour akin to pacing in mammals. As part of her PhD research, Melanie Denommé investigated the motivations behind IWB in bearded dragons (Pogona vitticeps; Figure 1) over a three year period, and formally tested whether it stems from a “desire” to escape their enclosures.

Figure 1. Photo of a bearded dragon interacting with a barrier (called glass surfing sometimes if the lizard moves back and forth across the transparent barrier, although reptiles may do this on non-transparent barriers as well).

Our findings revealed a strong preference for performing IWB near the front barrier of their environment (Figure 2), the only known escape route; even when half of it was obscured; they also direct more of their behaviour toward the transparent part of the front barrier. Interestingly, IWB was 15 times more likely to occur around the time when lizards defecated, supporting an argument that these behaviours may be driven by escape-related motivations, at least with respect the need to find suitable defecation areas.  However, no clear link was found between IWB and anticipation of feeding, suggesting species-specific differences in how repetitive behaviours are triggered. Despite these results, lizards would still exhibit IWB with non-transparent barriers (Figure 2), suggesting that escape is not the exclusive explanation for these repetitive behaviours.

Figure 2. Results from multiple rounds of home cage observations of barrier wall interaction (minutes per day). Bearded dragons interacted more with the front barrier (that is, the barrier from which escape could occur), although still exhibited IWB (interacting with barriers) along the other 3 walls of the enclosure.

Seasonal and sex-related patterns offered further nuance. Contrary to expectations, female lizards performed IWB more during spring, while males showed consistent levels year-round. This might reflect frustrated breeding-season motivations, as females in the wild often roam widely in search of mates, a behaviour restricted in captivity. These findings emphasize the complex interplay between natural instincts and captive conditions, highlighting the importance of tailoring environments to better meet the needs of individual animals. By understanding these behaviours and using an evidence-based approach, we can deepen insights into the diverse causes of repetitive behaviours across species and thereby improve captive reptile welfare.

Note that the actual levels of IWB seen were low throughout the study, with numerous animals never performing the behaviour. There appear to be individual differences in the expression of IWB.

Citation

Denommé, M and Tattersall, GJ. 2025. Investigating the motivations of repetitive barrier interactions in Pogona vitticeps. Applied Animal Behaviour Science, 283: 106484. https://doi.org/10.1016/j.applanim.2024.106484

Ultraviolet Sensing Behaviour in Bearded Dragons

/ gtattersall

Exposure to ultraviolet (UV) light has both physiological benefits as well as costs. Many lepidosaur reptiles can behaviourally self-regulate their exposure to UV light in order to take advantage of the benefits of UV light while minimizing the costs. Furthermore, lepidosaur scales have been conceptualized by some as a barrier to the penetration of UV light.

In a recently published study, we (Nick Sakich, recent graduate from the lab) examine regulation of self-exposure to UV light in three different phenotypes of Bearded Dragon (Pogona vitticeps): wild type, animals exhibiting scales of reduced prominence (‘Leatherback’), and scaleless animals (‘Silkback’). These scaleless mutants have arisen in the captive reptile husbandry industry. All phenotypes were tested in a 3 chamber system, offered 3 different intensity of standard basking lamps to assess how long they spent under each UV lamp.

Silkbacks on average chose to expose themselves to lower levels of UV light irradiation than Leatherbacks or wild types did, which suggests that the ability for UV to penetration through the skin is diminished in normal scaled phenotypes.

Simultaneously, we tested their self-exposure behaviour while they were able to choose cold or warm temperatures. Bearded Dragons of all scalation phenotypes received higher UV irradiation when they were in the cold section of a UV gradient apparatus compared to when they were in the hot section of the apparatus. This either demonstrates that Bearded Dragons under higher UV irradiances choose cooler temperatures or demonstrates that Bearded Dragons at cooler temperatures choose higher UV irradiances. The relationship between chosen temperature and chosen UV light irradiance was not affected by scalation phenotype.

This study highlights external influences on the mechanism that regulates UV self-exposure behavior in lepidosaur reptiles. Scales are apparently a barrier to UV absorbance, and thus scaleless lizards need to adjust their time exposed to UV light.

One logical interpretation the temperature sensitive UV seeking behaviour shows evidence that when cold, lizards may adopt UV seeking behaviour in an attempt to bask (i.e. an attempt to warm up) as would happen in the wild when basking in the sun. In our study, the UV bulbs were fluorescent bulbs and not radiant bulbs, and thus lizards may spend preferentially more time exposed to UV as part of their natural basking behaviour.

Figures and citation are provided below:

Wildtype Bearded Dragon (juvenile)
Leatherback phenotype of bearded dragon (juvenile)
Silkback phenotype of bearded dragon (juvenile)
Ultraviolet light test chamber involve 3 separate ‘basking’ sites partitioned within a circular chamber. Bearded dragons were free to move between the partitions due to gaps underneath the vertical baffles. The floor was kept at the preferred temperature (35°C) within the red zone, and allow to fall to room temperature (22-24°C) outside of that zone. This created allowed us to track the UV preferences while lizards were selecting warm or cool temperatures.

For those wishing to see a pdf of our article, for the next 50 days, free access is available at the following link: https://www.ichthyologyandherpetology.org/ihbjbb/ovh2020134ug688044yq

Alternatively, please request access to a pdf from Researchgate.

Citation

Sakich, N and Tattersall, GJ. 2022. Regulation of exposure to ultraviolet light in bearded dragons (Pogona vitticeps) in relation to temperature and scalation phenotype. Ichthyology and Herpetology, 110: 477-488. https://doi.org/10.1643/h2020134

Lizard Chapter Published

/ gtattersall

A book on the “Behavior of Lizards: Evolutionary and Mechanistic Perspectives” (Eds. Vincent Bels and Anthony Russell) has just been published with a chapter from my lab!

https://www.crcpress.com/Behavior-of-Lizards-Evolutionary-and-Mechanistic-Perspectives/Bels-Russell/p/book/9781498782722

Chapter 1: Behavioral thermoregulation in lizards: Strategies for achieving preferred temperature – Ian R.G. Black, Jacob M. Berman, Viviana Cadena, and Glenn J. Tattersall

This work was primarily the result of collaborative work of my former graduate students, Ian Black, Jacob Berman and Viviana Cadena. I am very grateful to have great graduate students willing to work on these projects.

If you are interested in accessing this chapter, contact me by email or on researchgate.