Ultraviolet Sensing Behaviour in Bearded Dragons

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.


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

Thermal adaptations best explain biogeographic rules in Australian shorebirds

Bergmann’s and Allen’s rules state that endotherms should be larger and have shorter appendages in cooler climates. However, the drivers of these rules are not clear. Both rules could be explained by adaptation for improved thermoregulation, including plastic responses to temperature in early life.

Our study has just been published in Nature Communications here:


Non-thermal explanations are also plausible as climate impacts other factors that influence size and shape, including starvation risk, predation risk, and foraging ecology. In this study, we assess the potential drivers of Bergmann’s and Allen’s rules in 30 shorebird species using extensive field data (>200,000 observations). We show birds in hot, tropical northern Australia have longer bills and smaller bodies than conspecifics in temperate, southern Australia, conforming with both ecogeographical rules.

Heat map of Australia, including the sample sites where morphological data from >30 species of shorebirds were used.

This pattern is consistent across ecologically diverse species, including migratory birds that spend early life in the Arctic. Our findings best support the hypothesis that thermoregulatory adaptation to warm climates drives latitudinal patterns in shorebird size and shape.


Dr. Alexandra McQueen (Post-Doc at Deakin University) did most of the work on this manuscript. The Victorian Wader Study Group and the Australasian Water Studies Group were responsible for the 46 years worth of data collected that made this study possible. My thanks to Matt Symonds and Marcel Dekker for including me in this study, a result made possible from an Australian Research Council Discovery Grant.


McQueen A, Klaassen M, Tattersall GJ, Atkinson R, Jessop R, Hassell CJ, Christie M; Victorian Wader Study Group; Australasian Wader Studies Group, Symonds MRE.  2022. Thermal adaptation best explains Bergmann’s and Allen’s Rules across ecologically diverse shorebirds. Nat Commun 13, 4727. https://doi.org/10.1038/s41467-022-32108-3