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Long‐term datasets are required to understand the response of long‐lived organisms (e.g., gopher tortoises [Gopherus polyphemus]) to management actions, such as prescribed burns. Our objective was to estimate the effects of prescribed burning on gopher tortoise population dynamics over decadal time frames at Fort Stewart Army Reserve, southeastern Georgia, USA. We captured and marked adult tortoises from 1994–2020. In addition, since the early 1990s, managers at Fort Stewart collected spatial records of prescribed burns; thus, we could compare demography of the population to prescribed burning. We used a Bayesian hierarchical model (open population Jolly‐Seber model) to estimate population parameters (emigration and survival, immigration and recruitment, and adult abundance) and their relationships with years since burn. We observed opposing responses to years since burn at 2 sites: abundance and the probability of staying (survival plus not emigrating) increased within 1 site when it had been more recently burned (F zones), but abundance and probability of staying in a second site increased when it had been longer since the site was burned (E zones). Some of these effects were weak but indicative of different responses to burning between the sites. Although the sites experienced similar burning regimes, they differed substantially in other habitat features: the F zones had almost twice the tree cover and lower soil sand composition, indicating that tortoise population responses to burning depend on habitat context. We inferred that the primary mechanism for demographic responses to years since burn was likely emigrating adults, which indicates the need for more detailed movement data. Our results demonstrate that gopher tortoise population responses to prescribed burning are complex, context dependent, and primarily influenced by tortoise movements. Therefore, prescribed burn plans may best accommodate spatially dynamic tortoise populations when they create spatial heterogeneity in burn ages within the range of typical tortoise movements. © 2021 The Wildlife Society. Gopher tortoises at 2 sites exhibited opposing population responses to prescribed burning, with differences likely attributable to habitat differences between the 2 sites. Tortoise populations likely responded to burning through increases or decreases in emigration; therefore, prescribed burn plans should be designed to accommodate spatially dynamic tortoise populations, allowing tortoises to select burn ages that are the most beneficial given other habitat conditions.

Plasma triacylglycerol, phospholipid, cholesterol, cholesterol esters, fatty acids, and total lipids were measured in 30 female and 20 male desert tortoises (Gopherus agassizii) during the annual reproductive cycle in the eastern Mojave desert, Nevada. Blood samples were collected at monthly intervals from April to October. All lipid fractions, with the exception of free fatty acids, were significantly higher in female plasma than in male plasma in all months of the year. In contrast, free fatty acids were higher in male plasma than in female plasma in all months. The seasonal pattern in estradiol secretion mirrored that of triacylglycerol, phospholipid, cholesterol, and total lipid, all of which showed a significant correlation with the hormone. Estradiol and the vitellogenesis-associated lipids were all significantly higher in August, September, October, and April than in June. The seasonal variation in cholesterol ester levels in females did not correlate with any of the reproductive events and did not appear to be involved in yolk precursor formation. Total lipid in males showed a negative correlation with testosterone and spermatogenesis. Individual fatty acids in the June and August samples (at the highest and lowest estradiol levels) were compared in male and female plasma. The percent of C18:3n3, C18:2n6, C18:1n9, C20:5n3, and C22:5 were significantly higher in the June female plasma sample than in the August sample. Docosahexanoic (C22:6n3) acid was barely detectable in female plasma in either month. J. Exp. Zool. 293:703–711, 2002. © 2002 Wiley-Liss, Inc.

The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied during the 1996–1997 and 1997–1998 nesting seasons at Los Baulas National Park, Playa Grande, Costa Rica. Blood samples were collected from nesting females throughout the season. Females were observed to nest up to 10 times during the nesting season. Plasma steroids were measured by radioimmunoassay and total plasma calcium was measured by flame atomic absorption spectrophotometry. Plasma testosterone and plasma estradiol levels declined throughout the nesting cycle of the female. Testosterone declined from a mean of 10.18 ± 0.77 ng/ml at the beginning of the nesting cycle to 1.73 ± 0.34 ng/ml at the end of the nesting cycle. Estradiol declined in a similar manner, ranging from a mean of 190.95 ± 16.80 pg/ml at the beginning of the nesting cycle to 76.52 ± 12.66 pg/ml at the end of the nesting cycle. Plasma progesterone and total calcium levels were relatively constant throughout the nesting cycle. Lack of fluctuation of total calcium levels, ranging from a mean high of 97.46 ± 11.37 μg/ml to a mean low of 64.85 ± 11.20 μg/ml, further suggests that vitellogenesis is complete prior to the arrival of the female at the nesting beach. Clutch size (both yolked and yolkless eggs) did not vary over the course of the nesting cycle.

Blood samples from 30 female and 20 male adult desert tortoises, Gopherus agassizii, were collected at monthly intervals during the annual reproductive cycle (April to October). Plasma corticosterone and the sex steroids in each of the samples were analyzed by radioimmunoassay. Mean corticosterone levels in males were significantly higher than in females (P < 0.001) in every month. Male tortoises showed a marked seasonal pattern in plasma corticosterone with a highly significant peak in July, August, September, and October that corresponded with a similar peak in plasma testosterone. Testosterone and corticosterone in the male showed a highly significant correlation (P < 0.0001). The pattern of corticosterone in the female was less marked, with a significant peak in May during the mating and nesting season, but no association with the peak in estradiol in late summer was apparent. The highest levels of corticosterone in the males were associated with the peak in spermatogenesis and intense male–male combat. These results support similar data from other reptiles that suggest increased glucocorticoid secretion during periods of increased activity and metabolism. J. Exp. Zool. 289:285–289, 2001. © 2001 Wiley-Liss, Inc.

To characterize seasonal changes in thyroid function in a terrestrial reptile, thyroid hormones were measured over a period of 2 years in desert tortoises, Gopherus agassizii, maintained at the Desert Tortoise Conservation Center in Las Vegas, Nevada. In all samples, triiodothyronine was nondetectable (less than 0.1 ng/ml). Thyroxine (T4) exhibited distinct cycles in both sexes, being lowest during hibernation and rising toward the time of emergence. Females exhibited only one peak in T4, during the early spring. In males, T4 levels peaked in early spring and again in late summer. The desert tortoise has distinct activity patterns that include increased feeding, mating, and locomotor activity in the early spring and increased mating and combat in the late summer. In an experiment to determine whether food intake influences T4, food was withheld for 2 weeks. Compared to continuously fed controls, T4 declined significantly in unfed tortoises, but increased significantly within 36 h of refeeding, indicating that thyroid activity is responsive to nutrient intake. The second seasonal peak of T4 only in males suggests that male reproductive activity in late summer is associated with thyroid activation. To evaluate this possibility, adult, subadult, and juvenile males were sampled during the months of the second seasonal peak in T4. Although all three age groups showed similar foraging and thermoregulatory behaviors, T4 peaked in July only in the reproductively active adults, which also exhibited significantly higher testosterone levels. Elevated T4 in desert tortoises is thus associated with periods of increased feeding and reproductive activity, supporting a role for thyroid hormones in these energy-demanding activities.

The seasonal reproductive cycle of the Kemp's ridley sea turtle (Lepidochelys kempi) was studied under semi-natural conditions at the Cayman Turtle Farm, Grand Cayman, British West Indies, from June 1987 to July 1988. MaleL. kempidisplayed a prenuptial rise in serum testosterone 4 to 5 months prior to the mating period (March). Male testosterone then declined sharply during the mating period. FemaleL. kempialso displayed a prenuptial rise in serum testosterone, estradiol, and total calcium 4 to 6 months prior to the mating period (March). Female testosterone and estradiol declined during the nesting period (April to July) immediately following the mating period (March). Elevated levels in female estradiol and total calcium corresponded with the period of vitellogenesis as determined from gel electrophoresis and ultrasonography. Serum thyroxine also fluctuated seasonally with elevated levels observed in females associated with the period of vitellogenesis.L. kempidisplayed a distinct seasonal reproductive cycle in captivity. Nesting in the captive study group corresponded with nesting in the wild population at Rancho Nuevo, Mexico (April to July). Female endocrine cycles during the nesting period were similar to those observed in the wild population.

The reproductive physiology of nine Galápagos tortoises (Geochelone nigra) was studied from February 1988 to May 1989. The study encompassed the annual reproductive cycle to include complete mating and nesting sequences. Male (n = 4) and female (n = 5) seasonal reproductive changes were determined throughout the study with endocrine analysis and ultrasonographic examinations. Males displayed a prenuptial rise in serum testosterone (x― ±SE = 6.62 ± 0.92 ng/ml in August) during which gonadal maturation and spermatogenesis are thought to occur. The male reproductive cycle appears consistent with the prenuptial spermatogenic pattern exhibited by other tropical turtles. In the females, testosterone rose during the mating period (x― ± SE = 499.3 ± 124.6 pg/ml in October) prior to ovulation and is probably related to receptivity in the females. Progesterone was more variable, but also peaked during the mating period (x― ± SE = 1,017.2 ± 220.6 pg/ml in October) and appears related to ovulation. Estradiol rose several months prior to mating (x― ± SE = 75.5 ± 11.9 pg/ml in July) and was correlated with increased serum calcium levels. This increase in estradiol is thought to stimulate vitellogenesis several months prior to mating. Nesting occurred from November 1988 to April 1989, during which six clutches were laid. Clutch size ranged from eight to 17 eggs. Both male and female Galápagos tortoises display seasonal physiological changes that function to regulate annual reproductive patterns. Zoo Biol 17:505–517, 1998. © 1998 Wiley‐Liss, Inc.