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. 2025 Jun 5;20(6):e0322682.
doi: 10.1371/journal.pone.0322682. eCollection 2025.

Influence of enclosure design on the behaviour and welfare of Pogona vitticeps

Affiliations

Influence of enclosure design on the behaviour and welfare of Pogona vitticeps

Melanie Denommé et al. PLoS One. .

Abstract

Complex or naturalistic enclosures have become increasingly accepted as those best-suited to improve an animal's welfare. However, designing such enclosures can be difficult if little is known about the animal in the wild, and enclosures that aim to replicate natural habitats must still be assessed to ensure their assumed benefits are realized. Therefore, this study examined the behaviour and physiology of captive-bred bearded dragons (Pogona vitticeps) living in naturalistic- and standard-style enclosures. First, we assessed whether naturalistic-style enclosures better accommodated a lizard's behaviour by examining if lizards in these enclosures were inactive for a similar amount of time as their wild counterparts, if they used their enclosures more evenly than standard-housed lizards, and if naturalistic enclosures provided better thermal heterogeneity than standard enclosures. Then, we examined if living in naturalistic-style enclosures improved the lizard's welfare by examining behaviours related to stress and relaxation as well as heterophil to lymphocyte (H:L) ratios. Although naturalistic enclosures did offer better thermal heterogeneity, evidence that they better accommodated a lizard's behaviour or improved their welfare was equivocal: lizards spent the majority of their day inactive, in one area of the enclosure, and performed similar amounts of behaviours related to stress and relaxation, regardless of enclosure style. Furthermore, H:L ratios were only lower for female lizards in naturalistic enclosures. Our results may have been influenced by the timeline of data collection but could also suggest that standard enclosures are sufficient for P. vitticeps, that P. vitticeps perceive standard- and naturalistic-style enclosures as similar, or that the potential benefits of naturalistic enclosures were hampered by the enclosure's size. Ultimately, it was apparent that structural complexity alone was insufficient to influence lizard welfare, highlighting the importance of considering the animal's motivations throughout their life and aspects other than enrichment for effective enclosure design.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Images of standard (A) and naturalistic (B) enclosures in which Pogona vitticeps were kept.
Standard enclosures included a paper substrate and paper hide (visible in the front left). Naturalistic enclosures included a loose substrate, cork bark (visible in the back left), paper hide (not visible; used to prop up cork bark) and a naturalistic hide (visible in front left). Both enclosure styles included a ceramic tile, food bowls, and water bowls. Images were taken from video recordings by TLC200 Pro Brinno cameras and therefore have a minor fisheye-lens distortion.
Fig 2
Fig 2. Demarcation of the 4 quadrants used to assess enclosure use in Pogona vitticeps.
In this figure, a standard-style enclosure is seen. Quadrants were based off the dimensions of the tile, which was almost exactly as large as ¼ of the area of the enclosure. A tile and basking lamp are present in the back right quadrant, a food bowl is present in the front right quadrant, a water bowl spans the front left and right quadrants, a paper hide is present in the front left quadrant, and the back left quadrant is empty.
Fig 3
Fig 3. Thermal image with the area that was used to assess substrate temperature highlighted in white.
In this figure, a naturalistic-style enclosure is seen. This region of interest excluded the tile, the lizard, any furnishings (i.e., cork bark, naturalistic hide) and the area at the front of the enclosure with the food and water bowl.
Fig 4
Fig 4. Percent time inactive in Pogona vitticeps was mostly independent of enclosure design or sex.
Percent of known time P. vitticeps were inactive in either naturalistic or standard enclosures (A – D) or between female and male lizards (E – F). Lightly-coloured dots represent individual values and colour-coded dashed lines represent mean values. A black dashed line at 80% is provided as a reference to the amount of inactivity typical of wild P. vitticeps estimated from [37]. Data in plots (A) and (E) were collected when lizards were sub-adults and had been in their enclosure style for at least 148 days (Naïve time point). Data in plots (B) and (F) were collected when lizards were adults (~365 days old) within a week of their swap to the opposite enclosure style (Swap time point). Data in plots (C) and (G) were collected when lizards were around 530 days old and had been in their enclosure style for at least 170 days (Experienced time point). Data in plots (D) and (F) were collected when lizards were over 2 years old and had been in their enclosure style for at least 418 days (Long-term response point). Timelapse cameras were used to record behaviour, and percent of known time inactive represents the amount of time lizards spent either immobile or hiding within the camera’s view. Wilcoxon one-sample tests found that inactivity was always greater than 80% (p < 0.001 for all groups). Generalized linear models found that inactivity only differed between enclosure styles (p = 0.04; B) and sexes at the swap time point (p = 0.03; F).
Fig 5
Fig 5. Performance of behaviours related to relaxation independent of enclosure design and sex in Pogona vitticeps.
Proportion of P. vitticeps that were inactive and leg stretched (ILS) for at least 5% of their observed day between naturalistic and standard enclosures (plots A – D) or between female and male lizards (plots E – H) at 4 different points in time. White boxes with numbers inside of coloured-in or lightly-coloured areas provide the count of lizards that either performed ILS for at least 5% of their day (coloured-in area) or did not (lightly-coloured area). Numbers above bars in each plot provide the total number of lizards in each group. Data in plots (A) and (E) were collected when lizards were sub-adults and had been in their enclosure style for at least 148 days (Naïve time point). Data in plots (B) and (F) were collected when lizards were adults (~365 days old) within a week of their swap to the opposite enclosure style (Swap time point). Data in plots (C) and (G) were collected when lizards were around 530 days old and had been in their enclosure style for at least 170 days (Experienced time point). Data in plots (D) and (F) were collected when lizards were over 2 years old and had been in their enclosure style for at least 418 days (Long-term response point). A logistic regression was performed to compare the number of lizards performing ILS between groups but found no influence of sex or enclosure style at any point in time (p > 0.05).
Fig 6
Fig 6. Performance of behaviours related to stress unaffected by enclosure design and mostly independent of sex.
Percent of known time Pogona vitticeps interacted with barriers (IWB) in either naturalistic or standard enclosures (A – D) or between female and male lizards (E – F) at 4 different time points. Lighter-coloured dots represent individual values and colour-coded dashed lines represent mean values. Data in plots (A) and (E) were collected when lizards were sub-adults and had been in their enclosure style for at least 148 days (Naïve time point). Data in plots (B) and (F) were collected when lizards were adults (~365 days old) within a week of their swap to the opposite enclosure style (Swap time point). Data in plots (C) and (G) were collected when lizards were around 530 days old and had been in their enclosure style for at least 170 days (Experienced time point). Data in plots (D) and (F) were collected when lizards were over 2 years old and had been in their enclosure style for at least 418 days (Long-term response point). Generalized linear models were used to compare data between groups within each plot; only an influence of sex was detected at the swap time point (F). At this time point (F), compared to female lizards, male lizards performed IWB for less time (p = 0.04).
Fig 7
Fig 7. Enclosure use patterns in Pogona vitticeps housed in naturalistic- or standard-style enclosures.
Percent of a 12-hour day that Pogona vitticeps spent in one of four quadrants in either naturalistic (orange) or standard (blue) enclosures at 4 different points in time. Filled-in dots with lines above and below represent transformed model estimates and 97.5% confidence intervals. Lighter-coloured dots represent individual data points. Images below the x-axis highlight the main or only feature in that quadrant and are colour-coded based on enclosure style where relevant (i.e., in the front left quadrant, only naturalistic enclosures had the leftmost/orange hide; only standard enclosures were empty in the back left quadrant). A dotted horizontal line at 25% is included to visualize the amount of time lizards would spend in each quadrant if their behaviour was evenly distributed. Generalized linear mixed models were used to assess time in each quadrant between enclosure styles and included a random intercept for lizard ID. Enclosure style did not influence time in any quadrants at any time points (p > 0.025). At each time point, lizards spent the majority of their time in the back right quadrant (colour-coded ***p < 0.001).
Fig 8
Fig 8. Naturalistic-style enclosures provide greater variability in substrate temperatures compared to standard-style enclosures.
Standard deviation of substrate temperatures in either naturalistic (orange) or standard (blue) enclosures at 4 different times of day. Filled-in dots with lines above and below represent model estimates and 95% confidence intervals; lighter-coloured dots represent individual data points from enclosures. At each time of day, the substrate from 12 enclosures of each type were measured. Regardless of the time of day, the standard deviation of substrate temperatures was lower in standard enclosures compared to naturalistic enclosures (Linear mixed model, p < 0.001). Although the standard deviation of substrate temperatures tended to increase over time, a significant difference was only detected between 0900 and 1500 (p = 0.006).
Fig 9
Fig 9. Average temperature of the tile (basking area) throughout the day in naturalistic- and standard-style enclosures.
Temperatures were measured using thermal imaging and at each time of day, 11 enclosures of each style were measured. Solid dots represent the mean temperature of all enclosures of that style for that time of day. Lines above and below this point represent the 95% confidence interval of this mean. Lighter-coloured dots represent individual within each enclosure.
Fig 10
Fig 10. Heterophil to lymphocyte (H:L) ratios of male or female Pogona vitticeps in naturalistic- or standard-style enclosures.
Filled-in dots with lines above and below represent transformed model estimates and 95% confidence intervals. Lighter-coloured dots represent individual data points. Colour-coded text above the x-axis provides sample sizes for each group. Blood cells were counted by an individual blind to the lizard’s sex and enclosure style, and lizards had lived in a particular enclosure style for at least 600 days (~19 months) prior to collection of blood samples. Ratios were analyzed using a generalized linear model with an interaction between enclosure style and sex. Within female lizards, those living in naturalistic enclosures had lower H:L ratios than those in standard enclosures (p = 0.032). Within standard enclosures, male lizards had lower H:L ratios than females (p = 0.011).

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