Abstract
The gopher tortoise (Gopherus polyphemus) is a long-lived terrestrial ectotherm that is native to the southeastern coastal plains from Louisiana to peninsular Florida. While this species has been well studied at higher latitudes above the freeze line, populations residing towards the southern edge of the species’ range remain understudied. To bridge this gap in knowledge, I documented year-round variation in gopher tortoise activity within a population in Southwest Florida. I hypothesized that gopher tortoises would remain active outside their burrows year-round, with their activity positively influenced by increases in temperature and solar illumination, and negatively affected by increased precipitation. Using carapace-mounted light sensors, I tested this by recording the intensity of solar light to which a tortoise was exposed in order to quantify its daily activity duration and burrow occupancy.Gopher tortoise activity patterns varied significantly throughout the year. During colder months, tortoises spent longer periods of time under direct sunlight outside of their burrows. In warmer months, tortoises visited their burrows nearly twice as often while residing partially within their burrow entrances for greater portions of the day. Interestingly, while the proportion of daylight hours spent above ground did not differ between the coolest months (winter) and the warmest months (summer), a significant decrease occurred during the spring. Notably, tortoises displayed consistent year-round activity, never remaining underground for more than five consecutive days. Temperature and solar illuminance were the strongest predictors of emergence, with a 3.7°C increase in temperature above the documented 15.8°C emergence threshold increasing the likelihood of departure by 72% (Harris et al., 2015). Likewise, an 11,343-lux rise in sunlight intensity increased departure likelihood by 38%, potentially serving as a cue for individuals as they detect subtle variations in reflected light near the burrow entrance. Temperature, light, and precipitation together explained for only 9.5% of the variance in daily activity duration, with a significant interaction suggesting their combined effects are more important than each factor independently. Other unmeasured variables, such as conspecific interactions or unique physiological needs, may better explain the remaining variation.
In contrast to northern populations within the species range that may undergo several months of extended brumation, gopher tortoises in Southwest Florida expressed continuous above-ground activity throughout the year. This supports the concept of extended breeding seasons and likely influences resources allocated for uninterrupted growth, potentially resulting in larger individuals on average in areas where forage remains consistently abundant year-round. These findings deepen our understanding of the distinct behavioral adaptations of southern populations compared to their northern counterparts and underscore the need for region-specific management strategies that account for the differing environmental influences shaping gopher tortoise populations across their range.