Effects of husbandry practices on Komodo dragon (Varanus komodoensis) behavior and welfare: a multi-institutional evaluation

Habitat design plays a critical role in regulating overall welfare of ex situ populations. However, despite having a higher reliance on their environment, the role of habitat design and components has been largely understudied in reptiles. To address this, a study was designed to evaluate the behavioral response of Komodo dragons (Varanus komodoensis) to different light and heat provisioning within habitats. Twenty facilities participated in the study. Overall behavior was assessed from a filtered dataset of 35 Komodo dragons from 19 facilities, and habitat analysis used a subset from 15 facilities (26 Komodo dragons) that provided both husbandry and behavioral data. This analysis evaluated the effect of indoor and outdoor habitats, natural lighting, and access to artificial light and heat sources. Komodo dragons were grouped by maturity and sex to assess demographic-based variation in behavioral response to habitat type. Komodo dragon activity budgets were primarily composed of inactive behaviors across the study period and observations of undesirable behaviors were low. Outdoor habitats and habitats with natural light were associated with higher activity levels in immature Komodo dragons, while mature Komodo dragons were most active in indoor habitats and habitats without natural light. In indoor habitats, access to infrared light and heated surfaces both increased activity levels in females, but not males, and access to ultraviolet B light increased activity levels consistently across the study sample. The findings of this study establish a behavioral baseline for the human-managed population of Komodo dragons and demonstrate that simple habitat design components, namely whether they were indoors or outdoors, natural and artificial light access, and supplemental heat availability, exert a significant influence over their behavior. These results can be used to inform management practices to promote a high standard of welfare in this species.

Identifying the factors that shape animal welfare is a critical component of sustaining healthy populations in modern zoos and aquariums. Contemporary frameworks evaluate animal welfare on a continuum, prioritizing both the mitigation of negative stressors and the presence of quantifiable positive indicators (Broom, 1988; Mellor, 2016, Mellor, 2017). Achieving this requires a strong understanding of species-specific indicators and the husbandry conditions that drive them (Melfi, 2009; Yeates and Main, 2008). Although numerous factors are evaluated towards this goal, behavioral observations have emerged as a vital, non-invasive, and accessible tool for assessing welfare (Bacon, 2018; Dawkins, 2004; Silvestre Martínez, 2014; Warwick et al., 2013). Consequently, understanding the behavioral impacts of husbandry is essential to creating evidence-based practices that better support the welfare of animals in human care (Binding et al., 2020; Ward et al., 2018; Whitham and Wielebnowski, 2013).

Behavioral indicators of welfare have primarily been studied in mammals, leaving reptile welfare comparatively understudied (Benn et al., 2019). This gap reflects the historical reliance on anthropocentric and domestic mammal-based welfare models that often fail to capture the distinct biological needs of ectotherms (Benn et al., 2019; Melfi, 2009; Binding et al., 2020). Of the few studies, positive indicators of welfare include high rates of exploration and diverse thermoregulatory displays (Benn et al., 2019), and undesirable indicators include unproductive, repetitive interactions with habitat boundaries (Warwick et al., 2013; Whittaker et al., 2021). In reptiles, behavioral thermoregulation is critical to metabolic, immune, and digestive processes (Adkins et al., 2003; Baines et al., 2016; Kane et al., 2023). The expression and duration of thermoregulatory behaviors are influenced by external temperature and light wavelengths (Kane et al., 2023; Tosini and Avery, 1996), and may vary by sex and body size (Harlow et al., 2010a, Harlow et al., 2010b; Juri et al., 2018). Restricted or altered thermoregulatory behavior can limit the individuals ability to maintain appropriate temperatures and support a number of crucial physiological process including vitamin D synthesis and reproduction (Acierno et al., 2008; Baines et al., 2016; Chiaraviglio, 2006; Ferguson et al., 2010; Rodríguez-Díaz and Braña, 2011). As these behaviors are linked to environmental conditions, the method and frequency by which they are expressed can provide important information about the suitability of the habitat and resulting welfare status of managed reptiles (Melfi, 2009).

As an iconic, charismatic reptile, the Komodo dragon (Varanus komodoensis) presents an ideal opportunity to evaluate the effect of habitat design on reptile welfare. Komodo dragons are popular among zoos and private collections (Koch et al., 2013; Komodo Dragon SSP Sustainability Report, 2024). Internationally, 284 animals are held at Species360 participating institutions (Species360, 2026), yet their welfare in human care remains comparatively understudied (but see: Carbajal et al., 2018; Gillespie et al., 2000; Gyimesi and Bums, 2002; Waterman et al., 2021; Wood et al., 2023; Zimmerman et al., 2022), and the population exhibits low growth rates and survivorship (Laver et al., 2012; Mendyk, 2015; Zimmerman et al., 2022). Endemic to the Lesser Sunda Islands, this species is the world’s largest lizard by weight, exhibiting a size range from 0.1 kg hatchlings to adults exceeding 87 kg (Harlow et al., 2010b; Jessop et al., 2021). This species is described as a “mid-day open sun basker” and thermoregulator in the wild, with high UV requirements (UVI: 2.6 - 3.5, Max 4.5 - 9.5) (Baines et al., 2016; Ferguson et al., 2010). Consequently, Komodo dragons exhibit a range of behavioral and thermoregulatory adaptations as they transition from small, sun-shuttling arboreal lizards that occupy lower levels of the food web to terrestrial top predators that maintain body temperatures through basking and their high thermal inertia (Auffenberg, 1981; Harlow et al., 2010a; Imansyah et al., 2008; Purwandana et al., 2016).

These challenges underscore the need to understand how habitat design and husbandry protocols support thermoregulatory behavior and welfare across life stages. The specialized ecological requirements of Komodo dragons have led to substantial variation in habitat design across ex situ populations, providing a valuable opportunity to evaluate behavior across differing lighting and thermal conditions. Habitat design shapes the environmental conditions animals experience and should aim to approximate those of their native range (Arena and Warwick, 1995; Guillette et al., 1995; Lillywhite and Gatten, 1995). Despite recent advancements, artificial features are limited in their ability to meet this goal (Baines et al., 2016; Mendyk et al., 2014; Warwick et al., 2013). A growing body of literature identifies ultraviolet B (UVB) exposure (Gillespie et al., 2000; Wood et al., 2023; Zimmerman et al., 2022) and thermal gradients (Mendyk et al., 2013) as important regulators of behavior and health. However, few studies have examined how specific components of habitat design influence activity patterns across ex situ Komodo dragon populations, particularly across life stages (Baines et al., 2016).

This study investigates the relationship between habitat design, behavior, and welfare in Komodo dragons. Using a multi-institutional study design, we leveraged an expanded sample size to examine associations between activity patterns and specific habitat conditions. Specifically, we assessed the effects of habitat location (indoor vs outdoor) and the availability of supplemental light and heat on Komodo dragon activity across sex and age classes. Characterizing behavioral responses to these environmental features provides essential baseline data to support the development of evidence-based management protocols and improve outcomes for the ex situ Komodo dragon population.

This study was reviewed and approved by the North Carolina Zoo’s Research Review Committee and by institutional research review committees at participating facilities, as required.

Data collection

Multi-institutional behavior study

Using the ZooMonitor (Lincoln Park Zoo, 2022) application’s Community platform, behavioral data were collected between May and September 2025 by observers at 19 participating AZA facilities in the United States (response rate = 95%) (Supplementary Table 1). Behaviors were recorded based on an ethogram (Supplementary Table 2) modified from previous behavioral research on monitor lizards (Varanus) (Huo et al., 2024; Fauzia et al., 2024; Reh et al., 2021; Waterman et al., 2021; Wood et al., 2023). To ensure consistency of data collection across observers, we created and implemented a multi-step training and testing process prior to live data collection (see Wark et al., 2021, for details). Observers (n = 56) were required to score an average of 85% or higher across a series of video interobserver reliability tests before data collection began, and observers scored an average of 92% across all tests.

Observers recorded data every minute, for five minutes, relying on established behavioral focal sampling methods (Altmann, 1974). Observations were conducted 3 days per week across 3-time blocks: morning (8:00 - 11:00), afternoon (11:00 - 14:00), and evening (14:00 - 17:00), to adequately represent daily behavior across the week and control for management differences across time of day. Teams were asked to redo sessions where the focal individual was consistently watching the observer.

Multi-institutional husbandry survey

A Qualtrics-based survey (Qualtrics, Provo, UT) was used to collect husbandry data. Sixteen facilities completed the survey (response rate: 80%), providing detailed information for 34 Komodo dragons (77.3% of the sample) (Supplementary Table 1). Respondents were asked to provide information on habitat types and lighting schemes that play a critical role in reptile welfare (Supplementary Survey) (Kane et al., 2023; Fleming, 1977; Mendyk et al., 2013; Oonincx and van Leeuwen, 2017; Reh et al., 2021; Zimmerman et al., 2022).

Statistical analyses

All statistical analyses were performed using the software R (v 4.4.1; R Core Team, 2024). All visualizations were made with the package ggplot2 (Wickham and Chang, 2016). Across all analyses, age thresholds for maturity were set at seven years for females and eight years for males (Jessop et al., 2021; Jirik, 2026; Laver et al., 2012).

Descriptive behavior analyses

Nineteen zoos participated in our behavioral study, collecting data on 35 Komodo dragons. This group included 25 mature (Males, n = 14; Females, n = 11) and 10 immature animals (Males, n = 7; Females, n = 3). We removed behaviors scored as “not visible”, “other”, and “not recorded” from all analyses (3.8% of all intervals).

Our analyses grouped behaviors into three categories: inactive (n = 12,255), active (n = 4,414), and undesirable (n = 147). Inactivity encompasses basking, which, though stationary, is an intentional and vital thermoregulatory behavior. Although the behavior in the undesirable category, barrier-oriented behavior (see Supplementary Table 2), describes an animal in an active state, this behavior was important to evaluate separately, given its established association as potential negative indicator of welfare (Warwick et al., 2013; Whittaker et al., 2021). To quantify time budgets per individual, we calculated the proportion of each observation session spent in each behavioral category and then averaged these proportions across all recorded sessions (Wark and Cronin, 2024).

Habitat analyses

To explore links between habitat conditions and behavioral profiles, our study sample relied only on those individuals for which we have a complete set of both behavior observations and husbandry surveys (see Supplementary Table 3 for sample sizes).

We constructed generalized linear mixed models (GLMMs) with a binomial distribution using the ‘lme4’ package (Bates et al., 2015) because the dependent term, “Behavior Category”, was binary (active, n = 3068; inactive, n = 9008). Undesirable behaviors were rare (0.5% of habitat-linked observations) and were therefore excluded. We relied on the Akaike Information Criterion (AIC) (Arnold, 2010) to conduct model selection, comparing models including the individual terms of interest, interactions between the terms, single term models, and the null model (Bartoń, 2025). Individual zoo and Komodo dragon identity were tested as random effects in all models, where Komodo identity was determined to maintain the lowest AIC (ΔAIC > 116). To ensure the independence of variables, correlations between fixed effects were examined via the model’s variance-covariance matrix (Bates et al., 2015). If correlated (>0.5), terms were split into separate models for testing. Following model fitting, we utilized the emmeans package (Lenth, 2024) to calculate estimated marginal means back-transformed from the logit scale to the response scale (probability). We performed pairwise comparisons using the ‘ratio’ contrast method to calculate odds ratios and standard error (Hosmer et al., 2013).

Demographic models

To test the relationship between maturity, sex, and behavior, GLMMs with a binomial distribution were constructed, with our full model including maturity and sex as fixed effects. We assessed behavior independently of habitat in this model, so habitat was added as a random effect (along with focal ID) to control for its influence.

Indoor vs outdoor habitats

To assess the effect of indoor and outdoor habitats on behavior, we explored the impact of outdoor spaces vs. indoor spaces on behavioral profiles. Habitat location was evaluated to contrast the physiological impacts of stable, controlled indoor environments with the dynamic environmental conditions characteristic of outdoor settings, both of which have the capacity to alter thermoregulatory and behavioral profiles of the species (Walsh et al., 1999; Wood et al., 2023). Habitats with access to both indoor and outdoor spaces for >50% of the time were scored as “Both” (Supplementary Table 4). As animals in “Both” habitats consistently had access to an outdoor space, and the connection between these spaces would introduce heterogeneity to the indoor component that wouldn’t have been otherwise seen in habitats scored as “Indoors”, “Both” habitats (n = 3) were grouped with “Outdoors” for our analysis. Our full model included the following fixed terms: habitat location, maturity, and sex.

Natural light

To assess the effect of natural light availability within a habitat on behavior, we included the following fixed effects: no natural light, filtered natural light, or natural light. The “natural light” category includes both indoor and outdoor spaces, as long as direct natural light was accessible to the animal. Natural light provided through UV transmissible materials was included as natural light for analysis due to a limited sample. Filtered natural light included habitats that provided natural light through transparent materials that filter out UV light. “No natural light” included indoor habitats that did not let in natural light (Supplementary Table 4). This was important to explore because each condition provides different access to wavelengths of light that influence reptile welfare (Baines and Cusack, 2019; Baines et al., 2016). To explore the effect of natural light on activity, the full model included the following fixed terms: natural light, maturity, and sex.

Artificial light

To assess the effect of artificial light, we evaluated indoor habitats separately. Indoor habitats were provided with infrared light (IR), ultraviolet B light (UVB), or a combination of both (Supplementary Table 4). Artificial lighting controls the environmental conditions of indoor habitats that regulate reptile behavior when natural light is not accessible (Baines et al., 2016; Wood et al., 2023). The full model included the following terms: IR light, UV light, sex, and maturity.

Heated surfaces

To assess the effect of heated surfaces on behavior, indoor habitats were further characterized by the presence or absence of heated surfaces (Supplementary Table 4). Heated surfaces are an additional way to provide heat to habitats. It is important to understand how these features affect behavior, as these warming methods are not typical for heliothermic reptiles (Mendyk et al., 2014; Mendyk et al., 2013). The full model included heated surface, maturity, and sex as fixed effects.

Overall behavior

Overall, 3,459 focal observation sessions were collected from 35 Komodo dragons across 19 facilities. Inactive behaviors accounted for an average of 72% of behaviors across observations (min = 30.7%, max = 93.2%, SD = 15.1%). The remaining time was allocated to active (smean = 27.0%, min = 6.8%, max = 66.3%, SD = 14.4) and undesirable behaviors (mean = 1.1%, min = 0, max = 11.0%, SD = 2.0; Figure 1).

Within our inactive behavior groups, Komodo dragons laying down with their heads up (47.9%) or heads down (21.5%) were most frequently observed. Among active behaviors, standing (14.3%) and locomoting on the ground (6.7%) were the third and fourth most commonly observed behaviors, respectively (Figure 1). “Stand” was categorized as active due to the alert posture and muscle engagement required to maintain this position. The active behaviors, drink, feed, water locomotion, and visitor/keeper-oriented, comprised less than 1% of observations each. The undesirable behavior “barrier-oriented” was observed for approximately 1% of the overall observed time.

Demographics

To evaluate the relationship between demographic characteristics and activity levels, the final model included maturity only (estimate = -0.74, SE = 0.38, p = 0.0483). Post-hoc pairwise comparisons demonstrated that immature Komodo dragons were 2.09 times more likely to be active compared to mature individuals (OR = 2.09, SE = 0.771, p = 0.0447) (Figure 2).

Indoor vs outdoor habitats

To explore links between habitat location and activity, our final model included the term maturity × habitat interaction (estimate = -1.89, SE = 0.19, p < 0.001). Follow-up pairwise comparisons showed that among mature individuals, activity was higher in indoor than outdoor habitats (OR = 2.18, SE = 0.25, p < 0.001). In contrast, activity was lower in indoor habitats than outdoor habitats for immature individuals (OR = 0.33, SE = 0.05, p < 0.001). Consequently, immature dragons were 8.05 times more likely to be active than mature Komodo dragons in an outdoor habitat (OR = 8.05, SE = 3.1, p < 0.001), while activity in immature and mature dragons was not significantly different in indoor habitats (OR = 1.22, SE = 0.44, p = 0.584) (Figure 3).

Natural light

Our final model to evaluate the effect of natural light on activity included significant interactions for natural access × sex (estimate = -0.92, SE = 0.25, p < 0.001) and natural access × maturity (No Natural, estimate = 2.40, SE = 0.27, p < 0.001; Filtered, estimate = 2.17, SE = 0.28, p < 0.001). Post-hoc pairwise comparisons showed that the effect of natural light on activity levels varied significantly by maturity (Figure 4). Among immature Komodo dragons, individuals with natural light were 3.81 times more likely to be active compared to those with filtered natural light (OR = 3.81, SE = 0.88, p < 0.001), and 2.44 times as likely to be active compared to those without natural light (OR = 2.44, SE = 0.37, p < 0.001). Mature Komodo dragons without natural light were 1.96 times more likely to be active than those with filtered natural light (OR = 1.96, SE = 0.32, p < 0.001), and 4.50 times more likely to be active than those with natural light (OR = 4.50, SE = 0.97, p < 0.001). Consequently, in habitats with natural light, immature Komodo dragons were 6.52 times more likely to be active than mature Komodo dragons (OR = 6.52, SE = 2.40, p < 0.001), while activity levels between immature and mature individuals did not vary significantly in habitats with filtered natural light (OR = 0.74, SE = 0.28, p = 0.43), or without natural light (OR = 0.59, SE = 0.25, p = 0.212).

The effect of natural light on activity levels also varied by sex (Figure 4). Among female Komodo dragons, those without natural light access were 2.90 times more likely to be active than those with filtered natural light (OR = 2.90, SE = 0.57, p < 0.001), and 2.16 times more likely than those with natural light (OR = 2.16, SE = 0.39, p < 0.001). Probability of activity for male Komodo dragons were not significantly different in habitats with natural light than they were in habitats with filtered natural light (OR = 1.23, SE = 0.18, p = 0.34), or without natural light (OR = 1.17, SE = 0.21, p = 0.648). In habitats without natural light, female Komodo dragons were 2.46 times more likely to be active than males (OR = 2.46, SE = 0.94, p = 0.019), but there was not a significant difference in activity levels between habitats with filtered natural light (OR = 0.89, SE = 0.32, p = 0.751), or with natural light (OR = 0.97, SE = 0.33, p = 0.938).

Artificial light

Due to the high correlation (correlation = - 0.6) between IR and UVB light, the fixed effects from the full artificial light model were split into two models to evaluate the effect each condition had on Komodo dragon activity.

Infrared light

To evaluate the effect of infrared light on activity, our final model included the term sex × infrared light (estimate = -1.16, SE = 0.25, p < 0.001). Post-hoc pairwise comparisons showed that among females, activity was 4.25 times higher in habitats with Infrared light compared to those without (OR = 4.25, SE = 0.79, p < 0.001), whereas there was no significant difference among male Komodo dragons (OR = 1.34, SE = 0.24, p = 0.095). Activity levels did not vary significantly between females and males in habitats with infrared light (OR = 1.87, SE = 0.69, p = 0.091) or without (OR = 0.59, SE = 0.24, p = 0.185) (Figure 5).

Ultraviolet B light

In order to assess the effect of UVB light on activity, our final model only retained the UV light term (estimate = 1.04, SE = 0.16, p < 0.001). Post-hoc pairwise comparisons showed that among Komodo dragons in indoor habitats, those in habitats with UVB light were 2.82 times more likely to be active than those without (OR = 2.82, SE = 0.46, p < 0.001) (Figure 6).

Heated surfaces

To assess the relationship between heated surfaces and activity, our final model retained the term sex × heated surface (estimate = -0.75, SE = 0.25, p < 0.001). While the interaction was significant, these variables only improved the model fit by 3.3 units, as measured by AIC, compared to the null model. Post-hoc pairwise comparisons showed that among female Komodo dragons, activity was higher in habitats with heated surfaces compared to those without (OR = 1.69, SE = 0.34, p = 0.009). There was no significant difference between males with and without heated surfaces (OR = 0.80, SE = 0.12, p = 0.145) (Figure 7).

This study provides a baseline activity budget for zoo-managed Komodo dragons and suggests that habitat related management factors can influence behavior in measurable ways. Access to the outdoors, natural and artificial light, heat, maturity, and sex each played interacting roles in shaping Komodo dragon behavior. These findings can serve as guidance when designing habitats and managing Komodo dragons in human care.

Inactivity was the most frequently observed behavior. The main inactive behavior observed, laying down with head up, is described as a basking posture in the species (Auffenberg, 1981; Fauzia et al., 2024). While information on activity rates for wild Komodo dragons is lacking, observations of zoo housed monitors, including Komodo dragons, note they are less active compared to their wild counterparts (Gupta, 1997; Mendyk et al., 2013; Walsh et al., 1999). Compared to other reptiles, monitor lizards have a high metabolic rate that supports increased activity (Bartholomew and Tucker, 1964; Earll, 1982; Mendyk et al., 2014; Pough, 1983). If the ex situ population is showing higher inactivity rates, this could be driven by suboptimal lighting and heat which has been found to contribute to this trend in human managed reptiles as animals must dedicate more time to inactive basking to meet thermoregulatory requirements (Arena and Warwick, 1995; Auffenberg, 1981; Harlow et al., 2010b).

Observed active behaviors, including locomotion and exploration, accounted for 37.2% of overall activity and may indicate positive welfare states. While higher activity is not inherently indicative of improved welfare, wild Komodo dragons engage in high rates of these behaviors (Auffenberg, 1981; Imansyah et al., 2008); therefore, the expression of comparable behaviors under human care may indicate opportunities to perform species-specific behaviors, which may, in turn, reflect positive welfare (Benn et al., 2019; Melfi, 2009). The only behavior we categorized as undesirable behavior was barrier-oriented activity. When evaluating welfare, stereotypic behavior is generally considered detrimental when it makes up more than 10% of an activity budget (Clegg et al., 2015), so observing it at such a low frequency (~1%) across our sample indicates that its contribution to overall species welfare is likely minimal.

Immature Komodo dragons engaged in a higher percentage of activity compared to mature individuals. While daily activity rates are not available for the wild population, this difference has been established in the in situ populations, where age-related variation may be attributed to differences in body size, which influences predation risk, foraging strategies, and thermoregulatory needs (Auffenberg, 1981; Harlow et al., 2010a; Fauzia et al., 2024). With their smaller size and higher surface-area-to-volume ratio, immature Komodo dragons have lower thermal inertia and therefore experience rapid internal temperature fluctuations (Cecchetto and Naretto, 2015; Grigg et al., 1979; Harlow et al., 2010b; Schmidt-Nielsen, 1984). Immature individuals may compensate through frequent “sun-shuttling” between microclimates to maintain stable body temperatures (Harlow et al., 2010b). In contrast, we propose that mature Komodo dragons’ higher thermal inertia permits more sedentary thermoregulatory strategies, including prolonged basking, shade-seeking, mouth-gaping, and burrow use (Auffenberg, 1981; Harlow et al., 2010b; Walsh et al., 1999). While direct comparisons of activity between wild and captive populations are limited, the observed age-related differences suggest that managed environments can support natural thermoregulatory behavior across age groups.

Age-related differences in thermoregulatory behavior were especially apparent in outdoor habitats, where immature Komodo dragons exhibited higher activity and mature individuals were more inactive. This finding may be associated with to environmental variations (or lack thereof) experienced in each habitat type: outdoor habitats provide heterogeneous environments, dynamic lighting, and variable thermal conditions throughout the day (Walsh et al., 1999), whereas indoor habitats have stable, fixed light and heat (Baines and Cusack, 2019; Baines et al., 2016). Such differences can have a profound influence on locomotion and exploratory behavior (Nakamura et al., 2011; Razal et al., 2017; Ross et al., 2010; Wood et al., 2023). For immature Komodo dragons, which have lower thermal inertia, outdoor thermal heterogeneity and shifting light may encourage more frequent movement among basking sites, shaded areas, and other thermal zones to maintain suitable body temperatures (Auffenberg, 1981; Baines et al., 2016; Harlow et al., 2010a). In contrast, the greater thermal stability of mature Komodo dragons may allow them to remain inactive for longer periods while maintaining appropriate body temperatures, particularly when outdoor habitats provide broad thermal gradients and accessible cooling opportunities such as shade or burrows (Walsh et al., 1999).

This interpretation may also explain behavior patterns in indoor habitats, where mature individuals were more likely to be active and immature were less likely to be active compared to outdoors. Indoor systems provide essential heat and wavelengths, but may offer limited intensity variation, reduced coverage relative to body size, fewer combinations of light and heat, and less diverse cooling opportunities (Baines et al., 2016; Mendyk et al., 2014; Reh et al., 2021; Warwick and Steedman, 2023). For immature Komodo dragons, the absence of shifting light and thermal zones may reduce movement among basking sites, resulting in longer sedentary basking and lower overall activity. Mature dragons, however, may have fewer opportunities to cool after reaching preferred temperatures. Higher activity may therefore represent higher rates of compensatory activity as they seek suitable thermal conditions. Together, these opposing responses reduce age-related activity differences indoors, suggesting that more uniform indoor environments may not fully support the natural size-dependent thermoregulatory patterns observed under heterogeneous outdoor conditions.

Activity profiles of mature and immature individuals also differed with exposure to filtered natural light. There was no significant difference in activity of immature Komodo dragons in habitats with filtered and no natural light, while there was a change in mature individuals. Compared to habitats without natural light, habitats with filtered natural light have dynamic lighting characteristic of habitats with natural light. For mature Komodo dragons, this may create moving thermal zones, allowing sedentary thermoregulation similar to with natural light. Instead of following the light and increasing activity as would be expected of immature individuals, the stationary artificial UVB light provided in 100% of these habitats may be preferred and promote sedentary basking. Across age groups, no natural and filtered natural light did not supported the activity profiles observed in habitats with natural light, likely due to reduced intensity and wavelengths of light (Baines et al., 2016; Kane et al., 2023; Michael Burger et al., 2007).

In indoor habitats, the presence of artificial UVB light is correlated with increased activity levels. Access to UVB light facilitates vitamin D synthesis in reptiles (Acierno et al., 2008; Baines et al., 2016; Ferguson et al., 2010). In indoor habitats, access to artificial UVB may maintain vitamin D3 levels comparable to those in wild Komodo dragons (Gillespie et al., 2000), and promote activity levels similar to those in outdoor habitats (Wood et al., 2023). Providing UVB light indoors may increase basking efficiency, allowing individuals to reach adequate vitamin D levels faster and engage in higher rates of activity compared to individuals without UVB.

We also report a sex difference in activity with respect to heating opportunities in indoor habitats: females housed with infrared light or heated surfaces were more active than females without these features, whereas males showed no significant differences in activity between conditions. Although research into sex-based differences in this species is limited, we propose two potential, non-mutually exclusive explanations for this finding. First, though we do not have weight information on all individuals in this study, generally adult female Komodo dragons are smaller than males (Auffenberg, 1981; Laver et al., 2012). Such size differences may produce variation in thermoregulatory behavior similar to the maturity-related patterns described above. With increased temperatures and wider thermal gradients created by supplemental heat, the smaller females may reach optimal body temperatures faster, reducing basking time and supporting active heat-shuttling (Auffenberg, 1981; Cecchetto and Naretto, 2015; Grigg et al., 1979; Harlow et al., 2010b). Conversely, larger males with higher thermal inertia may be less dependent on environmental conditions and maintain consistent activity levels with or without these components (Auffenberg, 1981; Harlow et al., 2010b).

A second potential explanation may rely on reproductive requirements. Female oviparous reptiles often adjust thermoregulatory behavior during reproduction (Chiaraviglio, 2006; Rodríguez-Díaz and Braña, 2011), including shifts in preferred body temperature or reductions in the breadth of preferred thermal ranges (Juri et al., 2018; Mathies and Andrews, 1997; Stellatelli et al., 2024). If female Komodo dragons alter their preferred temperature range in a similar way, access to infrared light and heated surfaces may support these needs, allowing more efficient thermoregulation and increased activity while male behavior did not change. This may also explain increased female activity in habitats without natural light, where more stable artificial conditions may facilitate maintenance of a narrower preferred thermal range. Males did not differ across natural light conditions, suggesting a broader preferred thermal range. However, we need more detailed information about the weights of the animals in our sample, the reproductive status, and the body temperature of our sample individuals to further explore this effect.

We note several caveats when interpreting these results. Although multi-institutional studies allow access to larger sample sizes, we recognize potential observer drift and bias in sample size across conditions (Supplementary Table 3). While we had a large number of observers in our study, the extensive training process ensured they began collecting data the same way, and the relatively short 12 week data collection period for each team reduced the need for retesting. While uneven samples may influence results, it is also representative of the variety of ways this population is managed. To address this potential issue, we reduced potential bias by grouping individuals according to biologically meaningful and management-relevant criteria and by using statistical approaches designed to accommodate unbalanced data.

Our grouping of variables also limits interpretation of some specific components of these lighting features that can be important. The intensity and accessibility of artificial light features can impact the availability of the provided resources and the animals ability to use them. However, we favored the broader, but still biologically relevant, questions for our analysis due to their wider applicability to the diversity of management strategies we sampled and the low response rates to the more detailed questions. This also applies to our grouping of “Both” habitats with “Outdoor” habitats. While grouped to assess similarly heterogeneous conditions, it may alter the results from “Outdoor” habitats alone. To address this, models were re-rerun excluding “Both” habitats and all trends remained the same (estimate = -1.19, SE = 0.35, p < 0.001). Our data collection period and the availability of comparable wild behavioral assessments also restricts interpretation of overall behavior and seasonal changes. Teams collected data over the same season and interpretation of the baseline activity budget in relation to anecdotal behavioral profiles of other monitors and reptile welfare assessments is still a valuable addition to our knowledge of the ex situ population.

Based on our findings, we recommend that habitat design should consider the age class and sex of the occupant to most effectively support Komodo dragon welfare. Immature individuals should be provided with heterogeneous environments with dynamic lighting and complex thermal gradients with daily variety to support natural thermoregulatory strategies (Mendyk et al., 2014; Walsh et al., 1999). Mature Komodo dragons may benefit from more cooling opportunities created by wider thermal gradients or structural features like burrows (Auffenberg, 1981). Supplemental heat options may be particularly crucial for female Komodo dragons due to reproductive and size-based needs, though the mechanisms underlying this sex difference warrant further investigation (Mendyk et al., 2014).

Further research is required to uncover the specific mechanisms of these results and to fully assess drivers of welfare in this species. Prioritization of larger sample sizes and year-round observations to account for population-wide seasonal trends can help to fully understand Komodo dragon behavior in human care. Furthermore, integrating comparative data from wild activity budgets would provide a robust benchmark for connecting Komodo dragon behavior to welfare. Given that captive female Komodo dragons are prone to health complications (Laver et al., 2012; Zimmerman et al., 2022) that may be exacerbated by suboptimal thermal gradients (Mendyk et al., 2013), further research should assess sex-specific thermal requirements so husbandry protocols can be refined accordingly. While variables such as humidity, substrate, diet, and enrichment were beyond the scope of this study, investigation of these factors across a similar scale is necessary to develop evidence-based husbandry practices for the species. Overall, this study establishes a baseline activity budget for this species and provides valuable insights into how location, lighting, and heat influence Komodo dragon behavior, demonstrating the ability of multi-institutional projects to assess and refine current husbandry practices.