Jeff Goessling

As the climate continues to warm at an unprecedented rate, much research attention has been focused on climate responses in organisms. Climate responses in the egg stage are restricted to the mother’s choice of nest site in oviparous species without parental care, but can mothers choose nest sites that compensate for climate change effects on developing embryos? We studied nest site choice in the gopher tortoise, Gopherus polyphemus, near the hot end of the species range. We found 25 nests, of which 16 (64%) were located outside burrows (in or near the aprons, the mound of excavated sand at the burrow entrance), as is usually the case for the species. Surprisingly, however, we found nine nests (36%) inside burrows, a novel finding for the species. There was marked variation in the canopy openness of selected nest sites (mean = 42.0%; range 24–62%); openness values of nest sites generally fell between those of potential nest sites in the sunniest (mean =61%) and shadiest (15%) locations. Canopy openness and incident radiation intensity (IRI) were highly, significantly positively related for nest sites and potential nest sites and changed little over the incubation period. Collectively, our data reveal that mothers can reduce mean nest temperatures by ∼2.5–3 °C by nesting 1.5 m down the burrow, or by nesting in the shadiest locations within 50 m of their burrows. Wide variation in openness and IRI and their effects on nest temperatures suggests that, among generations, tortoise mothers have some scope to buffer their developing embryos against climate warming, provided that nest site choice behaviour is heritable and can evolve fast enough to keep pace with future warming. Our novel finding of nests inside burrows suggests that gopher tortoises may have a greater capacity to offset climate warming than most turtles, which do not excavate and inhabit burrows.
•Climate change exposes eggs of oviparous species to hotter temperatures.•Nest site choice is thus a key climate response in oviparous animals.•We found that gopher tortoises can nest in their burrows, not just near them.•Tortoises can depress nest temperatures by 2–3 °C by nesting in shade or in burrows.•Thus, they may be more resilient to climate change than most other turtles.

Studies concerning the social behaviours of non-avian reptiles have generally lagged behind other taxa, yet many reptiles are among the most globally threatened animal groups, and their behaviours are key to conservation successes. Herein, we utilized a captive-reared cohort of headstart Gopher Tortoises (Gopherus polyphemus) to test if these animals first discern soil type by social familiarity and/or tortoise exposure and then we tested how social familiarity and sibling status affected social behaviours between individuals. We found that headstart Gopher Tortoises preferentially chose familiar soil over soil that had never been in contact with a Gopher Tortoise, but they also preferred soil that had been in contact with non-familiar individuals over familiar soil. Tortoises displayed the social behaviour of sniffing disproportionately to non-familiar individuals, regardless of sibling status, over familiar individuals. Other social behaviours of nipping, chasing, headbobbing, and colliding were performed independently of social familiarity or sibling status. Taken together, this set of experiments demonstrates that Gopher Tortoises have a high degree of social nuance that is built upon familiarity, and these results could have direct effects on how to optimize headstarting protocols for restoring wild populations.

Studies concerning the social behaviours of non-avian reptiles have generally lagged behind other taxa, yet many reptiles are among the most globally threatened animal groups, and their behaviours are key to conservation successes. Herein, we utilized a captive-reared cohort of headstart Gopher Tortoises (Gopherus polyphemus) to test if these animals first discern soil type by social familiarity and/or tortoise exposure and then we tested how social familiarity and sibling status affected social behaviours between individuals. We found that headstart Gopher Tortoises preferentially chose familiar soil over soil that had never been in contact with a Gopher Tortoise, but they also preferred soil that had been in contact with non-familiar individuals over familiar soil. Tortoises displayed the social behaviour of sniffing disproportionately to non-familiar individuals, regardless of sibling status, over familiar individuals. Other social behaviours of nipping, chasing, headbobbing, and colliding were performed independently of social familiarity or sibling status. Taken together, this set of experiments demonstrates that Gopher Tortoises have a high degree of social nuance that is built upon familiarity, and these results could have direct effects on how to optimize headstarting protocols for restoring wild populations.
•Using a cohort of Gopher Tortoises temporarily raised in captivity for conservation, we found that individual tortoises preferentially chose to be on soil from non-familiar tortoises over their own soil and also tortoises avoided soil that had not come into contact with any Gopher Tortoise.•By separating clutch-mates at hatching, we isolated effects of social familiarity from maternal sibling status and found that Gopher Tortoises disproportionately displayed the social behaviour of sniffing non-familiar individuals, regardless of sibling status.•We found that non-familiar sibling pairs did not display any social behaviours differently than non-familiar non-sibling pairs, suggesting that sibling status is not a key social metric that assorts wild Gopher Tortoises into social groups.•Together, these results suggest that Gopher tortoises are both spatially and socially curious yet cautious in both navigating new environments (e.g., novel soil) and interacting with new individuals (e.g., non-familiar members of the same cohort).

Wildlife biologists choose monitoring techniques for threatened and endangered species that optimize time, resources, data quantity, and data quality. We compared 3 commonly used methods of assessing population size in gopher tortoises (Gopherus polyphemus), including burrow censuses, line-transect distance sampling (LTDS) surveys, and mark-recapture surveys. To test how season and year might affect the inferences from surveys, we conducted surveys across multiple seasons during a 2-year continuous interval. We found that mark-recapture estimates yielded tight and consistent estimates of population size, regardless of the statistical model used to analyze the mark-recapture data. Then, we compared results from the mark-recapture study to burrow censuses and LTDS surveys. Our comparison indicated that LTDS surveys had lower variation when the estimates from 2 consecutive years were pooled within each season. Burrow censuses consistently underestimated population size by approximately 19-35%, depending on the sampling year, and did not produce results with confidence intervals. Line-transect distance sampling surveys resulted in mean population size estimates that were consistently lower than mark-recapture results by approximately 9%, though LTDS 95% confidence intervals consistently included the mark-recapture estimate. Our results underscore how not all studies are optimized by using the same survey method. Our results also demonstrate the risk that single-visit population surveys likely underestimate population size, which has implications for the mitigation and translocation management of Gopherus tortoises as well as efforts to quantify the current status of Gopherus species.

Social network analyses are sparse, despite having great potential to illuminate intricate details of wildlife behavioral ecology and to inform basic conservation practices. Using social interactions recorded during 1 year of 5-second interval photography, we conducted social network analyses of Gopher Tortoises (Gopherus polyphemus). G. polyphemus are charismatic and declining mid-sized tortoises that are habitat specialists endemic to the southeastern United States. We also conducted a simultaneous radio-telemetric study of tortoises contained within our study population to ascertain whether home range location is consistent with membership in distinct tortoise social network communities. We found strong statistical support for the presence of nonrandom social networks that were derived from male-female mating relationships. The most parsimonious social network included two distinct “cliques” that were spatially segregated. Each clique contained a similar number of males and females. Understanding this basic aspect of tortoise behavior should be key in basic population biology, not only of turtles but also other reptiles. Our results should influence protocols for successful conservation of this keystone species.

The overlap between spatial and physiological ecology is generally understudied, yet both fields are fundamentally related in assessing how individuals balance limited resources. Herein, we quantified the relationships between spatial ecology using two parameters of home range (annual home range area and number of burrows used in one year) and four measures of physiology that integrate stress and immunity (baseline plasma corticosterone concentration [CORT], plasma lactate concentration, heterophil:lymphocyte ratio [H:L], and bactericidal ability [BA]) in a wild free-ranging population of the gopher tortoise (Gopherus polyphemus) to test the hypothesis that space-usage is correlated with physiological state. We also used structural equation modeling (SEM) to test for causative relationships between the spatial and physiological parameters. We predicted that larger home ranges would be negatively correlated to traditional biomarkers of stress and positively correlated with immunity, consistent with our hypothesis that home ranges are determined based on individual condition. Males had larger home ranges, used more burrows, and higher baseline CORT than females. We found significant negative correlations between lactate and home range (r = -0.456, df = 21, P = 0.029). CORT was negatively correlated with number of burrows used in both sexes (F = 7.322, df = 2,20, P = 0.003, Adjusted R² = 0.383). No correlations were observed between space use and BA or, notably, H:L. SEM models suggested that variation in number of burrows used was a result of variation in baseline corticosterone. The lack of a relationship between H:L and home range suggests that home range differences are not associated with differences in chronic stress, despite the pattern between baseline CORT and number of burrows used. Rather, this study indicates that animals balance tradeoffs in energetics, likely by way of baseline corticosteroid, in such a way as to maintain function across continuously variable home range strategies.