Relocate nests/eggs to a hatchery: Sea turtles
Overall effectiveness category Awaiting assessment
Number of studies: 22
Background information and definitions
Reptile nests may be relocated away from specific threats (e.g. egg collecting, flooding, erosion, predation, or being crushed on roads) and reburied in an organised ‘hatchery’. Hatcheries consist of a defined location on or near the nesting beach, well above the high tide line, that is often fenced and patrolled. Nests/eggs collected from the beach are then reburied within the hatchery, where they can be closely monitored.
Burying a potentially large number of nests/eggs within a relatively small area may present a number of risks, and the consequences of disturbances such as flooding or poaching could be particularly severe. Other environmental variables at the hatchery location (e.g. temperature and humidity) may also impact on the sex, size, shape, colour, behaviour, movement ability and post-hatching growth of the hatchlings (Warner & Andrews 2002, Booth et al. 2006), and should be carefully considered when selecting the location.
Due to the number of studies found, this action has been split by species group, though no studies were found for amphisbaenians. See here for: Tortoises, terrapins, side-necked & softshell turtles; Snakes & lizards; Crocodilians; Tuatara.
For studies that discuss moving nests/eggs to other locations on the beach, but not to a hatchery, see Relocate nests/eggs to a nearby natural setting (not including hatcheries), and for those that discuss the effects of relocating eggs into artificial settings, including into polystyrene boxes and other containers, see Relocate nests/eggs for artificial incubation.
Booth D.T. (2006) Influence of incubation temperature on hatchling phenotype in reptiles. Physiological and Biochemical Zoology, 79, 274–281.
Warner D.A. & Andrews R.M. (2002) Laboratory and field experiments identify sources of variation in phenotypes and survival of hatchling lizards. Biological Journal of the Linnean Society, 76, 105–124.
Supporting evidence from individual studies
A replicated study in 1983 on a sandy beach in Georgia, USA (Wyneken et al. 1988) found that relocating loggerhead turtle Caretta caretta nests to a hatchery resulted in similar hatching success compared to eggs relocated for artificial incubation. Hatching success was similar for eggs relocated to a hatchery (3,608 of 5,100, 71% of eggs hatched) and artificially incubated eggs (135 of 163, 83% of eggs hatched). Nine of 50 relocated clutches (18%) were partially destroyed by ghost crab Ocypode quadrata predation, cold weather or drifting sand. In 1983, all loggerhead turtle nests on one beach (53 nests) were relocated due to risk of total failure (due to predators, storm tides or poachers). Fifty clutches were reburied in hand-dug nests in a fenced area on a nearby dune and three clutches were placed in glass-fronted polystyrene incubators (38 x 38 x 19 cm). Hatching success was assessed after hatchlings emerged.Study and other actions tested
A replicated, randomized, study 1986 on a sandy beach in Rantau Abang, Malaysia (Chan 1989; same experimental set-up as Chan & Liew 1995) found that relocating leatherback turtle Dermochelys coriacea eggs to an on-beach hatchery resulted in similar hatching success compared to eggs that were incubated artificially in Styrofoam boxes. Hatching success was similar for eggs from the hatchery (13–92% of 23–25 eggs) and eggs from Styrofoam boxes (52–100% of 23–25 eggs). In addition, careful handling of eggs during the first five days of incubation did not affect hatching success (handled eggs: 70–100%; non-handled eggs: 52–100%). Eggs were collected from four natural nests (only yolked eggs of normal size) and four groups of eggs (23–25 eggs/group) were incubated in one of three treatments: an on-beach hatchery; in Styrofoam boxes with egg handling during the first five days; or in Styrofoam boxes with no handling (98 eggs/treatment). Eggs in the on-beach hatchery were buried 60 cm deep, and the nests were surrounded with chicken mesh after 50 days. Half of the Styrofoam boxes were kept in a well-ventilated shed, and the others were kept in an enclosed laboratory. Hatching success was measured by counting the number of hatchlings that emerged.Study and other actions tested
A replicated, randomized study in 1986 on a sandy beach in Rantau Abang, Malaysia (Chan & Liew 1995; same experimental set-up as Chan 1989) found that moving leatherback turtle Dermochelys coriacea eggs to an on-beach hatchery resulted in almost all female hatchlings, and that hatching success did not vary due to the number of eggs buried together in the hatchery. In total, 168 of 169 (99%) hatchlings were female, and the sex of one hatchling could not be determined. Hatching success was similar across all nest sizes (23–25 eggs: 13–48%; 48–50 eggs: 22–44%; 72–75 eggs: 9–51%; 96–100 eggs: 15–47%). In 1986, eggs were collected from a total of 13 natural nests and buried in groups of 23–25 (7 nests), 48–50 (3 nests), 72–75 (3 nests) or 96–100 eggs/nest (3 nests). From each nest, 2–20 hatchlings were selected for sexing. These hatchlings were euthanised in chloroform and sex was determined by removing and examining the gonads. Hatching success was determined by counting the number of hatchlings to emerge from each nest.Study and other actions tested
A replicated, controlled study in 1987–1993 on a beach in Bahia, Brazil (Marcovaldi & Laurent 1996), found that relocating sea turtle nests to an on-beach hatchery resulted in lower hatching success compared to nests left in situ (though some of these nests were protected or moved) for one of two species. Hatching success was lower for loggerhead turtle Caretta caretta nests in the hatchery (63%) than for nests left in situ (73%), though there was no significant difference for hawksbill turtles Eretmochelys imbricata (hatchery: 52%; left in situ: 61%). Hatching success was higher for loggerhead nests relocated within six hours of laying (69%) than for nests relocated more slowly (6–12 hours: 63%; >12 hours: 63%), but there was no significant difference for hawksbills (within six hours: 57%; 6–12 hours: 53%; >12 hours: 56%). In September–May 1987–1993, three sections of a beach were patrolled daily to record nesting events. Eggs from 1,659 nests on two sections of the beach (19 and 10 km long) were brought to a fenced hatchery located on a third section of the beach (14 km), where they were reburied (15 cm deep) and surrounded by plastic mesh cylinders (35 cm high, 60 cm wide). A further 514 nests were left in situ, but those at risk from predation were covered with a plastic mesh (100 x 100 cm), and those at risk from tidal flooding or human activity were relocated to another natural setting on the beach (number of nests not reported).Study and other actions tested
A replicated study in 1988–1997 on a sandy beach in Jalisco, Mexico (Garcıía et al. 2003) found that relocating olive ridley turtle Lepidochelys olivacea nests to an on-beach hatchery resulted in fewer nests being lost to erosion or predation, and similar hatching success compared to nests left in situ. None of 65 relocated nests were lost to erosion or predation, whereas only 36 of 65 (56%) nests left in situ survived. Hatching success was similar in relocated (59%) and in situ nests (66%). In August 1990, July 1991 and October 1994, a 3 km stretch of beach was patrolled for nesting turtles. Half of the nests discovered were relocated to the hatchery and half were left in situ (total of 18, 32 and 80 nests/year). The hatchery (10 x 35 m) was enclosed with a fence made of wire mesh and mosquito mesh (2.5 m high, 0.5 m deep). Hatchlings were counted and released on the beach, and nests were excavated to assess hatching success.Study and other actions tested
A replicated, controlled study in 2000–2002 on three sandy beaches in southwest Turkey (Başkale & Kaska 2005) found that relocating sea turtle nests to an on-beach hatchery may have resulted in higher hatching success compared to nests left in situ. Results were not statistically tested. Hatching success tended to be higher for relocated nests (89, 85 and 71% hatching success for 5, 37 and 6 nests respectively) compared to nests left in situ (68, 19 and 64% for 67, 40 and 97 nests respectively). For relocated nests, hatching success was not affected by time after laying that relocation took place (0–6 h: 89%; 6–12 h: 79%; 12–18 h: 70%). Nests considered to be in vulnerable locations were relocated to a hatchery. The hatchery (10 x 15 m) was enclosed by a plastic fence (2 cm mesh) that extended 0.5 m below and 2 m above the sand surface. Hatchlings were released manually from near original nest sites. Nests were monitored from June–September 2000–2002.Study and other actions tested
A replicated, controlled study in 1987–1995 on a sandy beach on Zakynthos Island, Greece (Kornaraki et al. 2006) found that relocating loggerhead turtles Caretta caretta nests to an on-beach hatchery resulted in variable hatching success compared to both nests left in situ and nests left in situ and covered with metal cages. Average hatching success in the on-beach hatchery varied from 51–75%, compared with 56–68% for in situ nests and 44–72% for in situ nests covered with cages. Hatching success in the hatchery was lower in one of eight years and higher in two of eight years compared to in situ nests. From 1988, nests located within 7 m of the sea and in danger of inundation were moved to a beach hatchery (77 nests) as were nests located near to invasive plants with root systems that may have grown into nests. From 1990, nests located in beach areas with tourists were protected by 50 cm circular metal mesh cages buried 15 cm in the sand (88 nests). A further 313 nests were left in situ. Nests were excavated following hatchling emergence to assess hatching success.Study and other actions tested
A replicated, controlled study in 2005 on Boavista Island, Republic of Cabo Verde, western Africa (Abella et al. 2007) found that relocating loggerhead turtle Caretta caretta eggs to an on-beach hatchery resulted in lower egg mortality than naturally incubated eggs from one of two beaches, and that delayed, careful relocations resulted in similar mortality compared to immediate egg relocations. Egg mortality was lower for hatchery nests (immediate non-careful relocation: 38%; delayed and/or careful relocation: 48%) compared to natural in situ nests on one other beach (79%), but similar to natural in situ nests on another beach (56%). Egg mortality was similar for immediate (38%) and delayed, careful (48%) relocation, and mortality was similar regardless of the length of the time delay (0–96 h after laying: 41–55% mortality). Eggs relocated to the on-beach came from nests laid in flood-prone or silty areas. Eggs from 50 nests were moved at 0, 12, 24, 84, and 96 post-laying (10 nests/treatment), and care was taken to keep eggs upright. Eggs from a further 134 nests were taken to the hatchery immediately after laying with no care taken to control egg vibration or orientation. Eggs from two other beaches (41 and 34 nests each) were left in the nests to incubate naturally. All nests were excavated five days after the last emergence to assess egg mortality.Study and other actions tested
A replicated, controlled study in 1990–2004 on one sandy beach on the Caribbean coast of Costa Rica (Chacón-Chaverri & Eckert 2007) reported that relocating leatherback turtle Dermochelys coriacea nests from areas at high-risk of erosion to an on-beach hatchery resulted in similar emergence success compared to nests in low-risk areas. Results were not statistically tested. Emergence success was similar for eggs in the hatchery (43%) compared to eggs from nests in low-risk areas of the beach (41%). In February–July 1990–2004, all nests laid in high-risk areas (within 100 m of a river mouth) were relocated to on-beach hatcheries. Hatcheries were fenced and staffed 24 h/day during the incubation period, and all reburied nests were surrounded by a metal mesh cylinder to exclude predators and a fine cloth mesh (1 mm) to exclude flies. In February–July 1990–2004, nest surveys were conducted every night between 20:00–04:00 h, and all nests were monitored four times/day.Study and other actions tested
A replicated, controlled study in 1991–2003 on eight sandy beach locations in Sergipe and Bahia, Brazil (Da Silva et al. 2007) found that relocating olive ridley turtle Lepidochelys olivacea eggs to a hatchery resulted in similar hatching success compared to nests left in situ in seven of 12 nesting seasons and lower hatching success in five of 12 seasons. In seven of 12 nesting seasons, hatching success was similar for nests in the hatchery (76–84%) and nests left in situ (76–85%). In five seasons hatching success was lower in on-beach hatcheries (73–80%) than in situ nests (81–85%; see original paper for details). Turtle nesting activity was monitored on eight stretches of beach (339 km total length) in 12 nesting seasons (September–March) from 1991/1992–2002/2003. Hired fishers surveyed the beaches every morning to locate, count and move nests at risk from a range of threats (including tidal inundation, predators, poaching, beach illumination or habitat alteration) to open beach hatcheries or other areas of beach. Nests not at risk were left in situ. Hatchery and in situ nests were excavated after emergence to determine clutch size and hatching success (hatchery: 160–969 olive ridley nests/year; in situ: 7–286 olive ridley nests/year).Study and other actions tested
A study in 1982–2005 on four beaches on the pacific coast of Mexico (Martínez et al. 2007) reported that after relocating leatherback turtle Dermochelys coriacea nests to an on-beach hatchery, some successfully hatched. Results were not statistically tested. Average hatching success/year was 35–53%. Over the course of the study, at least 639,000 eggs were moved to the hatchery, and at least 270,000 hatchlings were released in to the wild. Patrols of at least one of four beaches took place annually in 1982–2005. In 1997–2005, the survey protocol was standardized across all four beaches, and nightly patrols to search for nests took place in October–May at 20:00–05:00 h. Clutches of eggs were gathered as soon as possible after laying (normally within 1–2 hours) and reburied in a protected, fenced area. Hatchlings were released on emergence at a number of different locations on the beach.Study and other actions tested
A replicated, controlled, before-and-after study in 1999–2004 on a sandy beach in Guanacaste Province, Costa Rica (Piedra et al. 2007) found that relocating leatherback turtle Dermochelys coriacea nests to a hatchery or to other safe locations on the beach resulted in similar hatching and emergence success compared to nests left in situ. Results were not statistically tested, and no distinction made between nests relocated to the hatchery or to other locations on the beach. Hatching and emergence success were similar for relocated nests (hatching: 19–52%; emergence: 14–32%) and nests left in situ (hatching: 30–69%; emergence: 9–57%). In October–March 1999–2004, beaches were searched every night for nesting females. In 2001–2004, nests considered to be at high risk (within tidal zone, in areas of high pedestrian traffic, in vegetation, close to estuary) were relocated to a hatchery or to other safe places on the beach (86 nests), and other nests were left in situ (220 nests). Two days after emergence of the first hatchling, or 60 days after laying, nests were excavated to determine hatching and emergence success.Study and other actions tested
A replicated, controlled study in 2004–2011 along 100 km of sandy beach in Rio de Janeiro State, Brazil (Lima et al. 2012) found that relocating loggerhead turtles Caretta caretta nests to an on-beach hatchery resulted in lower hatching success compared to nests left in in situ. Hatching success was lower for hatchery nests than for nests left in situ in six of seven seasons (hatchery: 61–74%; in situ: 73–81%), and similar in one season (hatchery: 65%; in situ: 79%). In the nesting seasons of 2004–2011 beaches were patrolled daily, and nests were either moved to an on-beach hatchery (231–1,015 nests/season) or left in situ (8–316 nests/season). After hatchling emergence, nests were excavated to assess hatching success.Study and other actions tested
A randomized, controlled study in 2009–2010 on a sandy beach in East Java, Indonesia (Maulany et al. 2012) found that relocating olive ridley turtle Lepidochelys olivacea nests to an on-beach hatchery resulted in higher hatching success than for nests left in situ. The hatching success of nests moved to an on-beach hatchery was 54–73% of nests laid (2009: 39 of 53 nests; 2010: 30 of 56), whereas all nests left in place (11–19 nests/year) were lost to predation within one week of being laid and no eggs hatched. Olive ridley turtle nests laid in May–July 2009–2010 along an 18 km stretch of sandy beach in a national park were randomly selected to be moved to an on-beach hatchery (2009: 53 nests; 2010: 56 nests) or left in place (2009: 11; 2010: 19) within 200 m of the hatchery. Nests moved to the hatchery were buried 30 cm apart in artificially dug nests (40 cm deep). Nests left in place were excavated to count the number of eggs and re-buried. Some nests left in place were also protected using artificial nest covers (see original paper for details). All nests were temporarily covered prior to hatching to enable hatchlings to be counted. After emergence, all nests were dug up and unhatched eggs counted.Study and other actions tested
A replicated, randomized study in 2004 on a sandy beach in Terengganu, Peninsular Malaysia (van de Merwe et al 2013) found that green turtle Chelonia mydas hatchlings from hatcheries released immediately after emerging moved almost twice as fast and had better body condition than hatchlings that were held for 3–6 hours prior to release. Green turtle hatchling running speeds were higher when released immediately (0.12 m/s) compared to when they were held in the hatchery for 1 h (0.11 m/s), 3 h (0.8 m/s), or 6 h (0.7 m/s) before release. Hatchling body condition was similar for newly emerged hatchlings (4.67 g/mm) and hatchlings held for 1 h (4.66 g/mm), but lower for those held for 3 h (4.61 g/mm) or 6 h (4.55 g/mm). In July–October 2004, two hundred hatchlings from 10 hatchery nests (20 hatchlings/nest) were measured for running speed (time to run over a 1.6 m plastic gutter lined with sand, repeated three times/hatchling; see original paper for details) and body condition (ratio of hatchling mass to body length). Hatchlings were measured immediately following emergence or at 1 h, 3 h and 6 h following emergence (5 hatchlings/nest/time held).Study and other actions tested
A replicated study in 2004 on a sandy beach in Terengganu, Peninsular Malaysia (van de Merwe et al 2013) found that green turtle Chelonia mydas hatchlings excavated from hatchery nests immediately after most hatchlings in the nest emerged moved faster and had higher body condition than hatchlings excavated five days after most hatchlings emerged. Hatchlings excavated from nests immediately after the main clutch emergence (0.10 m/s) were faster than hatchlings excavated five days later (0.60 m/s) and had similar running speeds compared to hatchlings that emerged naturally within five days of the main emergence (0.11 m/s). Hatchlings that emerged with the main emergence were the fastest (0.12 m/s). Body condition of hatchlings excavated immediately (4.73 g/mm) was greater than hatchlings that were excavated five days later (4.39 g/mm) or that emerged naturally within five days (4.60 g/mm), and was similar to hatchlings from the main emergence (4.70 g/mm). In July–October 2004, hatchling running speed (time to run over a 1.6 m plastic gutter lined with sand, repeated three times/hatchling; see original paper for details) and body condition (ratio of hatchling mass to body length) was compared between hatchlings excavated immediately after the main emergence (124 live hatchlings from 19 nests); hatchlings excavated five days after main emergence (56 live hatchlings from 13 nests); hatchlings that emerged naturally within five days of the main emergence (16 hatchlings from 6 nests); and hatchlings from the main emergence (200 hatchlings, number of nests not provided). Up to 10 hatchlings were measured/category/nest.Study and other actions tested
A controlled, before-and-after study in 2005–2012 on a beach in Costa Rica (James & Melero 2015) found that relocating olive ridley turtle Lepidochelys olivacea nests to an on-beach hatchery with 24-hour monitoring resulted in similar hatching rates to nests that were left in situ but camouflaged. Results were not statistically tested. The emergence rate of hatchlings from hatchery nests was 77%, compared to 71% of hatchlings from camouflaged in situ nests. The authors reported that egg poaching reduced from 85% in 2005 to 10% of eggs in 2005–2012. Nesting activity was monitored by nightly beach patrols (four 4 h long patrols) in July or August–December in 2006–2012 (98–177 nests laid/year). Nests were either relocated to an on-beach hatchery (363 nests, 40% of total), or camouflaged and left in situ (595 nests, 61% of total) to discourage illegal collecting. Relocated nests were randomly allocated a 1 m2 plot in the hatchery and dug into the sand. The hatchery was monitored 24 hours a day during the nesting season. Hatchlings were monitored on emergence and nests were excavated after hatching due dates to check hatching success.Study and other actions tested
A controlled study in 2008 on a sandy beach in Boa Viste, Cape Verde (Marco et al. 2015) found that loggerhead turtle Caretta caretta nests relocated to beach hatcheries without ghost crabs Ocypode cursor had higher hatching success and lower predation rates compared to nests left in situ. Hatching success was higher in nests that were relocated to hatcheries (65% success) compared to nests that were left in situ (33% success). Ghost crab predation rates were lower in nests that were relocated to hatcheries (2%) compared to those that were left in situ (55%). Turtle nests were excavated to count the eggs and reburied in either a hatchery (20 nests) or in the same place without any protection (20 nests). Nests were monitored daily until emergence. Hatchlings were counted and released from hatchery on emergence. Hatchling tracks were counted from other nests. All nests were excavated after last emergence and remaining eggs counted for analysis.Study and other actions tested
A study in 1996–2011 on a sandy beach in Costa Rica (Munoz & Arauz 2015) found that the majority of olive ridley turtle Lepidochelys olivacea eggs relocated to a fenced on-beach hatchery hatched and most hatchlings made it to the sea. Of 1,703 olive ridley turtle nests relocated to a beach hatchery, 78% of eggs hatched (120,015 eggs) and 22% did not (33,986). Of the eggs that hatched, 77% (117,886) emerged successfully and made it to water and 1% (2,129) died. Of nests left in situ, 8 were predated and 566 experienced egg looting. In July–December 1996–2011, nesting activity was monitored by nightly beach patrols (two 3 h patrols/night, 2,401 nights and 2,535 successful nesting events). Turtles were individually marked when encountered (1,239 olive ridleys) and 1,703 (67%) nests (154,001 eggs) were moved to an on-beach hatchery on the beach behind the tide line within 6 h of being laid. The remaining nests (832, 33%) were left in situ. The hatchery was protected by a 2 m high fence buried 40 cm into the sand. Sand in the hatchery was replaced annually. Nests were excavated after hatching due dates to check hatching success.Study and other actions tested
Referenced paperMunoz S.V. & Arauz R. (2015) Conservation and reproductive activity of olive ridley sea turtles (Lepidochelys olivacea) in Punta Banco, a solitary nesting beach in south Pacific Costa Rica: Management recommendations after sixteen years of monitoring. Revista de Biología Tropical, 63, 383-394.
A randomized study in 2012–2013 on sandy beaches on the pacific coast of Mexico (Hart et al. 2016) found that relocating olive ridley turtle Lepidochelys olivacea nests to an on-beach hatchery resulted in similar hatching success compared to artificially incubating eggs in polystyrene boxes, although turtles from the hatchery had longer shells and faster crawl speeds. Hatching success was similar for nests in the hatchery (82%) and for those incubated in polystyrene-boxes (89% success). Hatchlings relocated to an on-beach hatchery had longer shells (41 mm straight carapace length) and faster crawl speeds (0.018 m/second) than those incubated in polystyrene boxes (length: 39 mm; crawl speed: 0.011 m/second). Carapace width, hatchling weight and righting response time were similar between hatchlings from the hatchery and polystyrene boxes (see original paper for details). In 2012–2013, eggs from 49 nests were moved to one of two treatments: buried in an on-beach hatchery (33 nests) or embedded in sand in polystyrene boxes (16 nests). Upon emergence and movement, ten hatchlings (489 individuals in total) were randomly chosen from each nest to measure size, weight, crawl speed and righting response.Study and other actions tested
A replicated, randomized, controlled, before-and-after study in 2013 on a sandy beach in Michoacán, Mexico (Herrera-Vargas et al. 2017) found that olive ridley turtle Lepidochelys olivacea hatchlings incubated in an on-beach hatchery weighed less and had elevated stress hormone levels on emergence compared to hatchlings from natural nests. Hatchery hatchlings weighed less (16 g) than natural nest hatchlings (17 g), although other measures of body size such as body length were similar between hatchlings (see paper for details). On emergence, hatchery hatchlings had higher stress hormone levels (corticosterone serum: 31 ng/mL) compared to natural nest hatchlings (27 ng/mL). On arrival at sea, hatchery hatchlings stress hormone levels did not increase compared to the levels at emergence (at sea: 32 ng/mL; emergence: 31 ng/mL), whereas natural nest hatchlings stress hormone levels did increase (at sea: 33 ng/mL; emergence: 27 ng/mL). In 2013, olive ridley turtle nests were relocated to an on-beach hatchery and reburied. Natural nests were located near the hatchery. Seventeen hatchlings each from three hatchery and three natural nests were captured randomly on emergence for to measure size and levels of stress hormones (corticosterone serum) (see original paper for details). A further 10 hatchlings from two hatchery nests and 18 from three natural nests were sampled for stress hormone levels on arrival at sea. These hatchlings were taken to a location 20 m from the sea and set free, and hormone levels were measured when they arrived at the sea.Study and other actions tested
Referenced paperHerrera-Vargas M.A., Meléndez-Herrera E., Gutiérrez-Ospina G., Bucio-Piña F.E., Báez-Saldaña A., Siliceo-Cantero H.H. & Fuentes-Farías A.L. (2017) Hatchlings of the marine turtle Lepidochelys olivacea display signs of prenatal stress at emergence after being incubated in man-made nests: a preliminary report. Frontiers in Marine Science, 4, 400.
A study in 2011 on a sandy beach in Mauritius (Hama et al. 2018) found that moving a green turtle Chelonia mydas nest to an on-beach fenced enclosure resulted in most eggs hatching and hatchlings reaching the sea. In total, 26 turtles hatched from 36 eggs, of which 23 were released and reached the sea (three hatchlings were predated by ghost crabs Ocypode cursor). The nest was located as part of a survey and eggs were placed into a 3 x 3 m fenced enclosure in the same formation as they had been found in.Study and other actions tested