Create artificial burrows

Supporting evidence from individual studies

1. A replicated study in 1980–1982 in five areas of pine forest in Mississippi, USA (Lohoefener & Lohmeier 1986) found that providing artificial burrows inside release pens when translocating gopher tortoises Gopherus Polyphemus tended to result in more successful translocations than releasing tortoises directly into the wild. Results were not statistically tested. When translocated gopher tortoises were released into artificial burrows within release pens before being released into the wild, 17 of 21 translocations were successful. Zero of three translocations were successful when tortoises were released into artificial burrows with no pen; one of five when released into a natural burrow with no pen; and zero of 11 when no burrow or pen was provided. Forty individually-marked adult gopher tortoises (some may have been captive releases) were translocated in spring–summer 1980–1982 (one tortoise = one translocation). Tortoises were released directly into artificial burrows in the wild (1 m deep; 3 tortoises); into artificial burrows in circular release pens (4–7 m diameter pens; 21 tortoises, pen removed after 2–4 weeks); into abandoned natural burrows in the wild (5 tortoises); or were released directly into the wild with no specific management (11 tortoises). Tortoises were monitored until late summer or early autumn in the release year and translocations were judged successful if after release in to the wild, previously abandoned burrows became active and a translocated tortoise was found in them, or new tortoise burrows were dug in areas without pre-existing tortoise populations. 

   Study and other actions tested

   Referenced paper

   Lohoefener R. & Lohmeier L. (1986) Experiments with gopher tortoise (Gopherus polyphemus) relocation in southern Mississippi. Herpetological Review, 17, 37-40.

2. A replicated, controlled study in 1995–1998 in a grassland site in South Australia, Australia (Milne et al. 2003) found that female pygmy bluetongue lizards Tiliqua adelaidensis using artificial burrows had better body condition and produced larger offspring than female lizards using natural burrows. Females observed in artificial burrows had a higher body condition index than those in natural burrows (data reported as statistical model result). Females in artificial burrows also produced heavier offspring (artificial: 1.7 g; natural: 1.5 g) with a higher body condition index (artificial: 2.7; natural: 2.6) than females in natural burrows, though snout-vent length of offspring and females was similar for both groups (offspring: artificial: 44.5 mm; natural: 44.4 mm; females: artificial: 97.9 mm; natural: 96.5 mm). Body condition of males was similar in artificial and natural burrows. One-hundred artificial burrows (10 m apart in 10 x 10 grid, 30 cm deep and 1.7 cm in diameter) were added in August 1995 to a 1 ha plot adjacent to a natural population. They were made by hammering a metal rod into the ground and inserting a hollow wooden tube. Burrows were monitored weekly using a fibre optic camera from September to May over a three-year period. Lizards were lured out of natural burrows (147 females, 124 males) or removed in the tube from artificial burrows (40 females, 49 males). 

   Study and other actions tested

   Referenced paper

   Milne T., Bull C.M. & Hutchinson M.N. (2003) Fitness of the Endangered Pygmy Blue Tongue Lizard Tiliqua adelaidensis in Artificial Burrows. Journal of Herpetology, 37, 762-766.

3. A controlled, before-and-after study in 2000–2002 in grassland in South Australia, Australia (Souter et al. 2004) found that the addition of artificial burrows resulted in an increase in the number of pygmy blue tongue lizards Tiliqua adelaidensis. The average number of lizards in plots with artificial burrows increased following installation of burrows (before:  1 lizard/plot; 4 months after: 4 lizards/plot; 7 months after: 7 lizards/plot), while numbers on the plots without artificial burrows remained stable through the three surveys (1.4; 1.4 and 1.5 lizards/plot). In April 2002 (after new juveniles have left birth burrow), plots with artificial burrows had more juveniles (3.5 juveniles/plot) than those with natural burrows only (0.9 juveniles/plot). The average number of lizards in natural burrows did not change significantly with year or treatment (0.8–1.5 lizards/plot). The experiment was conducted in a 300 x 140 m area adjacent to a 1 h monitoring area. Twenty-four 20 x 20 m plots were established with an average of 3–5 natural burrows of 12 cm or deeper. After an initial survey in August 2001, eighteen small (13 mm diameter, 30 cm deep) and 18 large (17 mm diameter, 30 cm deep) artificial burrows were added to 12 experimental plots. Burrows were monitored using an optical fiber scope. 

   Study and other actions tested

   Referenced paper

   Souter N. J., Bull M. & Hutchinson M. N. (2004) Adding burrows to enhance a population of the endangered pygmy blue tongue lizard, Tiliqua adelaidensis. Biological Conservation, 116, 403-408.

4. A replicated, controlled, before-and-after study in 2009 in grass, bare ground and tilled soil enclosures in southern Australia (Ebrahimi & Bull 2012, same experimental set-up as Ebrahimi & Bull 2013) found that translocated pygmy bluetongue lizards Tiliqua adelaidensis used artificial burrows, and lizards given supplementary food spent less time in open habitat away from the burrows. Of 2,298 recorded lizard behaviours, 1,352 were of lizards basking in burrow entrances before re-entering; 708 were of lizards fully emerging and returning to the same burrow; and 238 were of lizards emerging and entering a different burrow. Lizards provided with supplementary food spent less time out in open habitat than lizards that were not fed (see paper for details). In November 2009, sixteen lizards were captured and moved to a trial site in a zoo and placed in four 15 m enclosed cages (four lizards/cage). Cages contained short grass, bare ground and tilled soil. Artificial burrows were built from hollowed wooden poles (30 cm long, 3 cm diameter) pushed into grassy or tilled soil (82 burrows/cage). No burrows were present in the bare ground habitat. Lizards in two of the cages were provided supplementary food for seven days, then after a two-day break, lizards in the other two cages were provided supplementary food for seven days. Lizards were monitored by four surveillance cameras/cage during daylight hours from the second to seventh days of the feeding regime (12 days total). 

   Study and other actions tested

   Referenced paper

   Ebrahimi M. & Bull C.M. (2012) Food supplementation reduces post-release dispersal during simulated translocation of the endangered pygmy bluetongue lizard Tiliqua adelaidensis. Endangered Species Research, 18, 169-178.

5. A replicated study in 2009 in a grassy enclosure in South Australia, Australia (Ebrahimi & Bull 2013, same experimental set-up as Ebrahimi & Bull 2012) found that translocated pygmy bluetongue lizards Tiliqua adelaidensis used artificial burrows, and burrow use was similar whether lizards were confined to holding pen for one or five days prior to release. Lizards were observed basking at artificial burrow entrances 85% of the time and exiting burrows 14% of the time. Of movements to and from artificial burrows, 62% were lizards returning to the same burrow, 29% were lizards moving to new burrows in the centre of the enclosure and 9% were lizards moving to new burrows at the edge of the enclosure. Lizard movements between artificial burrows was similar between translocated lizards confined to a holding area with burrows for one or five days (data reported as model outputs). In October 2009, sixteen translocated pygmy bluetongue lizards were released into one of four cages in a zoo enclosure (4 lizards/cage). Each cage included a central grassy circle (4 m diameter) with artificial burrows (made from hollowed wooden rods pushed into the ground), surrounded by a strip of bare ground (5 m wide), encircled by a strip of marginal habitat (0.5 m wide) with artificial burrows. When lizards were released, all cages had a holding pen around the central grass areas. The pen was removed after one (two cages) or five days (two cages). Lizard activity was monitored by video cameras over 10 days and analysis of lizard behaviour was based on observations from days 6–10 of the study (capturing 3,535 activity events and 504 lizard movements). 

   Study and other actions tested

   Referenced paper

   Ebrahimi M. & Bull C.M. (2013) Determining the success of varying short-term confinement time during simulated translocations of the endangered pygmy bluetongue lizard (Tiliqua adelaidensis). Amphibia-Reptilia, 34, 31-39.

6. A replicated study in 2011 in laboratory conditions in South Australia, Australia (Staugas et al. 2013) found that pygmy bluetongue lizards Tiliqua adelaidensis preferred to use artificial burrows with a chamber at the end, regardless of the size of the chamber. (All results were presented as model outputs unless otherwise stated). Lizards spent more time in artificial burrows with chambers attached (196–354 minutes in burrows with tennis-ball chambers) compared to burrows without chambers (6–97 minutes in burrows without chambers). Lizards spent similar amounts of time in artificial burrows with large and small chambers and also did not show any preference for whether the burrow was lined with sand or not (data reported as statistical model result). In June–July 2011, five different artificial burrows were tested (all surfaces lined with glued-on sand unless otherwise stated): plastic tube without a chamber; plastic tube with tennis ball chamber; plastic tube with large chamber; plastic tube with small chamber; and a plastic tube with large container and no sand lining (see paper for tube and container dimensions). Eight of 12 wild-caught lizards were used in each trial (3–4 trials/lizard). Lizard responses were videoed for 6 hours/day over two days.

   Study and other actions tested

   Referenced paper

   Staugas E.J., Fenner A.L., Ebrahimi M. & Bull C.M. (2013) Artificial burrows with basal chambers are preferred by pygmy bluetongue lizards, Tiliqua adelaidensis. Amphibia-Reptilia, 34, 114-118.