Study

The Galápagos giant tortoises (Geochelone elephantopus) Part II: Conservation methods

  • Published source details MacFarland C.G., Villa J. & Toro B. (1974) The Galápagos giant tortoises (Geochelone elephantopus) Part II: Conservation methods. Biological Conservation, 6, 198-212.

Actions

This study is summarised as evidence for the following.

Action Category

Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation

Breed reptiles in captivity: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation

Head-start wild-caught reptiles for release: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation

Protect nests and nesting sites from predation using artificial nest covers: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation

Create artificial nests or nesting sites

Action Link
Reptile Conservation

Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation
  1. Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles

    A replicated study in 1966–1971 in an artificial incubating facility in Galápagos, Ecuador (MacFarland et al. 1974) found that eggs from five subspecies of Galápagos giant tortoise hatched successfully after artificial incubation. Results were not statistically tested. Hatching success of artificially incubated Geochelone elephantopus ephippium eggs was 51% (158 of 312 eggs), G. e. darwini eggs was 37% (44 of 118 eggs hatched, 83 embryos died, 71 infertile eggs), G. e. hoodensis eggs was 63% (20 of 32 eggs hatched, 28 embryos died, 46 infertile eggs), G. e. porteri eggs was 35% (6 of 17 eggs hatched, 11 eggs infertile), and G. e. chathamensis eggs was 100% (3 of 3 eggs hatched). Hatching success of G. e. ephippium and G. e. porteri eggs incubated in undisturbed natural nests in the wild was 82% (103 of 133 eggs hatched, 4 embyros died, 18 infertile eggs) and 76% (391 of 520 eggs hatched, 21 embryos died, 101 infertile eggs) respectively. In the 1969/1970–1970/1971 nesting seasons, giant tortoise eggs laid by G. e. ephippium (312 total eggs), G. e. darwini (118 total eggs), G. e. hoodensis (32 total eggs), G. e. porteri (17 total eggs) and G. e. chathamensis (3 total eggs) were transported to an artificial incubation facility (1–2 hours on foot and 5–6 hours by boat). Eggs were incubated in wooden boxes with a soil substrate (see original paper). Hatching success and egg fertility was compared between subspecies and to naturally incubated, undisturbed G. e. ephippium and G. e. porteri eggs laid in the same seasons.

    (Summarised by: Katie Sainsbury)

  2. Breed reptiles in captivity: Tortoises, terrapins, side-necked & softshell turtles

    A replicated study in 1965–1971 in a captive breeding facility in the Galápagos, Ecuador (MacFarland et al. 1974) found that Galápagos giant tortoise Geochelone elephantopus hoodensis bred in captivity. Over five nesting seasons, captive Galápagos giant tortoise females laid 19 nests in artificial nesting sites, two in natural nesting sites, and six clutches were laid on the surface of their enclosure (tortoises were unable to construct nests). For eggs that were collected and artificially incubated, 75% (24 of 32) were fertile and 63% (20 of 32) hatched successfully. In comparison, 80–86% (519 of 653 total eggs) of eggs from wild, undisturbed nests (of two other giant tortoise subspecies) were fertile, and hatching success was 76–82% (494 of 653 eggs) (results were not statistically tested). One male and ten female Galápagos giant tortoises were brought into a captive breeding enclosure to mate and nest from the 1967/1968 nesting season. In 1969/1970, 1970/1971 and 1971/1972 nesting seasons, artificial nest sites were provided (fine soil, minimum 3 m2 and 35–40 cm deep). Nests were excavated the day after being laid and moved for artificial incubation. Hatching success was evaluated for six clutches in the 1970/1971 nesting season (1–7 eggs/clutch) and compared to 81 clutches of Geochelone elephantopus porteri (520 total eggs) and Geochelone elephantopus ephippium (133 total eggs) laid in 1969/1970–1970/1971.

    (Summarised by: Katie Sainsbury)

  3. Head-start wild-caught reptiles for release: Tortoises, terrapins, side-necked & softshell turtles

    A replicated study in 1965–1972 in a captive rearing facility and on an island in Galápagos, Ecuador (MacFarland et al. 1974) found that around two thirds of head-started Galápagos giant tortoise Geochelone elephantopus of five subspecies survived captive rearing and that over half of released juvenile Geochelone elephantopus ephippium survived at least 8 months in the wild after release. Results were not statistically tested. At least 41% (51 of 124) of head-started hatchlings kept in outdoor seaside pens died within the first 18 months compared to 18% (31 of 172) reared indoors or in a bespoke rearing facility. From two releases of head-started individuals, 20 of 20 (100%) and 25 of 51 (50%) tortoises survived 8–10 month, and 12 of 20 (60%) survived at least 17 months. Authors reported no instances of ill health; that all recaptured tortoises had increased in size and weight; and that individuals from the first release were heavier five and 10 months after release than equivalent captive animals (see paper for details). In 1965–1971, giant tortoise hatchlings were reared in captivity (including some captive-bred and some wild caught hatchlings; see paper for subspecies). The 1965/1966–1967/1968 cohorts (124 hatchlings) were reared in outdoor fenced seaside pens. The 1968/1969 cohort (50 hatchlings) were reared indoors. From 1970 onwards all cohorts were reared in a bespoke facility (122 hatchlings). Twenty tortoises were released in December 1970, and 51 were released in May 1972, and all were monitored for up to 19–17 months.

    (Summarised by: Katie Sainsbury)

  4. Protect nests and nesting sites from predation using artificial nest covers: Tortoises, terrapins, side-necked & softshell turtles

    A replicated, site comparison study in 1964–1972 on three islands in the Galápagos, Ecuador (MacFarland et al. 1974) found that protecting Galápagos giant tortoise Geochelone elephantopus nests with rock-walled corrals reduced predation by feral pigs Sus scrofa. In 1964–1970, none of the giant tortoise nests (10–25/year) on one island protected using corrals were predated by pigs. In 1970–1972, one of 262 protected nests were predated by pigs compared to 23 of 29 unprotected nests. The authors reported that corrals did not prevent dogs Canis lupus familiaris accessing and destroying nests elsewhere. In the 1964/1965–1969/1970 nesting seasons, 10–25 giant tortoise Geochelone elephantopus porteri nests/year were protected from pig predation on Santa Cruz using corrals built with lava-rock walls (1.5–2 m diameter, 1 m high). Corral use was extended in the 1970/1971 and 1971/1972 nesting seasons to protect 262 nests of three subspecies of giant tortoise (G. e. porteri, G. e. vicina, G. e. darwini) on three islands (Santa Cruz, San Salvador and Isabela). In 1970, twenty-nine nests were not protected with corrals on Santa Cruz and hatching outcomes monitored. In 1971–1972, introduced mammals (pigs and goats Capra hircus) were also controlled by shooting.

    (Summarised by: Katie Sainsbury)

  5. Create artificial nests or nesting sites

    A replicated, before-and-after study in 1965–1971 in a captive breeding facility in the Galápagos, Ecuador (MacFarland et al. 1974) found that Galápagos giant tortoise Geochelone elephantopus hoodensis females successfully laid eggs when artificial nesting sites mimicking natural conditions were provided. Results were not statistically compared. During the first two nesting seasons, when no artificial nests were provided, females attempted to nest on successive evenings (approximately 20–30 nights attempted nesting/clutch) but eventually dropped eggs on the rocky surface (four clutches). After artificial nests without ideal substrate were provided, females attempted to nest on successive evenings (10–30 nights/clutch) and some eggs were deposited in artificial nesting sites (artificial sites: 2 nests; on rocky substrate: 2 nests). After provision of ideal soil substrate, nesting attempts were shorter (1–4 nights/clutch, rarely up to 12) and all eggs were deposited in artificial (17 nests) or natural sites (2 nests). One male and 10 female Galápagos giant tortoises were brought into a captive breeding enclosure to mate and nest from the 1967/1968 nesting season. In 1969/1970, three artificial nesting sites were built (coarse soil, minimum 3 m2 and 35–40 cm deep). These were removed in the 1970/1971 and 1971/1972 nesting seasons, and replaced with four artificial nest sites with fine soil identical to that found in the natural nesting area (all other dimensions the same).

    (Summarised by: Katie Sainsbury)

  6. Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles

    A replicated study in 1969–1971 in an artificial incubating facility in Galápagos, Ecuador (MacFarland et al. 1974) reported that Galápagos giant tortoise Geochelone elephantopus ephippium egg hatching success was higher when eggs were left longer in natural nests before being relocated for artificial incubation. Results were not statistically tested. Of artificially incubated giant tortoise eggs, 74% (43 of 71) moved at 10–15 weeks, 67% (4 of 6) moved at 7–9 weeks, 19% (5 of 29) moved at 4–6 weeks, and 19% (5 of 27) moved at 0–2 weeks hatched successfully. In undisturbed natural nests, 82% (103 of 133) of G. e. ephippium eggs and 76% (391 of 520) G. e. porteri eggs hatched. In the 1969/1970 and 1970/1971 nesting seasons, giant tortoise eggs were transported at 10–15 weeks (71 eggs from 16 clutches), 7–9 weeks (6 eggs from 2 clutches), 4–6 weeks (29 eggs from 6 clutches) and 0–2 weeks (27 eggs from 5 clutches) after laying to an artificial incubation facility. Eggs were incubated in wooden boxes with a soil substrate (see original paper). Hatching success was compared to clutches left undisturbed laid by G. e. ephippium (133 eggs from 26 clutches) and G. e. porteri (520 eggs from 55 clutches) in the same nesting seasons.

    (Summarised by: Katie Sainsbury)

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