Background information and definitions
Natural dens can reduce the vulnerability of animals to attack. Providing artificial dens and refuges may mimic natural dens, thereby reducing mortality as a result of predation. Refuges and dens may also provide protection from extreme weather conditions.
This intervention specifically covers situations where refuges or breeding sites are provided for existing wild mammal populations. For provision of refuges for translocated mammals, see Species Management - Release translocated/captive-bred mammals into area with artificial refuges/breeding sites. See also Provide artificial dens or nest boxes on trees for the specific intervention of providing boxes attached to trees.
Supporting evidence from individual studies
A replicated, randomized, controlled, before-and-after study in 1995 in a sunflower field in Buenos Aires Province, Argentina (Hodara et al. 2000) found that providing artificial refuges did not increase abundances of small vesper mice Calomys laucha or Azara's grass mice Akodon azarae. The number of small vesper mice one to two months after refuges were placed did not differ significantly between plots with (4) and without refuges (5–8), and had not differed before refuges were placed (refuge plots: 14; no refuges: 18). Similarly, the number of Azara's grass mice did not differ between plots with (9–30) and without refuges (5–20) one to two months after refuges were placed, and had not differed before they were placed (refuge plots: 37; no refuges: 34). In July 1995, 60 artificial shelters (12 cm long, 10 cm diameter tins with one entrance hole, provided with cottonwool and wrapped in paper and nylon bags) were half-buried at each of three randomly selected plots. Three other plots received no shelters. Mice were live-trapped for three consecutive nights in all six plots, one week before shelters were provided (late-July) and twice after (mid-August and early-September) using Sherman traps baited with peanut butter, laid 10 m apart in grids of 15 × 4 traps.Study and other actions tested
A study in 2000–2001 in a grassland and woodland reserve in Victoria, Australia (Michael et al. 2004) found that artificial log refuges were used by fat-tailed dunnarts Sminthopsis crassicaudata. Fat-tailed dunnarts were found beneath both recently placed (20 of 408 refuges) and old refuges (9 of 271 refuges) in grassland. However, introduced house mice Mus musculus were more often found beneath recently placed (10 of 408 refuges) than old refuges (1 of 271 refuges) in grassland. Fat-tailed dunnarts preferred Eucalyptus (34 of 447 refuges) to cypress-pine (9 of 684 refuges) posts, and preferred wider, more decayed posts with more holes (see paper for details). In May 2000, between 12 and 20 old white cypress-pine Callitris glaucophylla and Eucalyptus Eucalyptus sp. fence posts were placed in each of 91 quadrats (total 1,131 new refuges) throughout a 3,780-ha national park in grassland and woodland. Mammals were surveyed monthly, beneath both new refuges and beneath 271 old fence posts which had lain in the same grassland sites for more than 15 years. Surveys were conducted from June 2000 to January 2001 and between 08:00 h and 20:00 h.Study and other actions tested
A study in 2002–2004 in a grassland site in Texas, USA (McGee et al. 2006) found that artificial escape dens increased swift fox Vulpes velox survival rates. Average annual survival in plots with artificial escape dens (81%) was higher than in areas without such dens (52%). Six of 11 confirmed mortalities were due to predation by coyotes Canis latrans, three were of unknown causes, one died of natural causes and one was predated by a raptor. All mortalities were outside artificial den plots. Thirty-six artificial escape dens were installed 322 m apart in each of three 2.6-km2 plots within a 100-km2 study area. Two plots had established swift fox populations while the third did not. Each den was a covered, 4-m long, 20-cm diameter corrugated-plastic pipe with open ends. Fifty-five foxes were radio-collared and tracked, 2–4 times/week, for up to two years, between January 2002 and August 2004. Survival was estimated from 41 adult foxes (28 in artificial burrow plots, 13 in the study area but outside artificial burrow plots).Study and other actions tested
A controlled study in 2005–2007 in an open forest and scrubland site in Córdoba province, Spain (Catalán et al. 2008) found that a plot with artificial warrens, water provision and fencing to excluding ungulate herbivores had more European rabbits Oryctolagus cuniculus than did a plot without these interventions. The three interventions were all carried out in the same plot, so their relative effects could not be determined. Average rabbit pellet counts were higher in the plot where the interventions were deployed (first year: 0.33 pellets/m2/day; second year: 1.08 pellets/m2/day) than in the plot without these interventions (first year: 0.02 pellets/m2/day; second year: 0.03 pellets/m2/day). A 2-ha plot was fenced to exclude ungulates in March 2005. Rabbits and predators could pass through the fence. Five artificial warrens were installed and water was provided at one place. No interventions were deployed in a second, otherwise similar, plot. Rabbit density was determined by monthly counts of pellets, from March 2005 to March 2007, in 0.5-m2 circles, every 100 m, along a 1-km transect in each plot.Study and other actions tested
A replicated, site comparison study in 2007 of pasture and scrubland on 14 estates in central Spain (Fernández-Olalla et al. 2010) found higher usage of artificial warrens where rabbit Oryctolagus cuniculus abundance was highest and that occupancy of tube warrens was higher than of stone warrens or pallet warrens. In grid squares where artificial warrens were used by rabbits, more rabbit latrines were found (13.5 latrines/km) than in squares where artificial warrens were not used (3.2 latrines/km). Authors report that it is unclear if artificial warrens boosted populations or if warren usage reflected pre-existing population levels. Occupancy of tube warrens (67% occupied) was greater than of stone or pallet warrens (54% occupied). Tube warrens (120 installed) comprised a labyrinth of concrete tubes 1 m underground. Stone warrens (207) were c.5 m diameter, with stones arranged to leave galleries and holes. Pallet warrens (198) were at least four wooden pallets, covered with soil. Rabbit latrines were surveyed along fixed routes within 98 squares in a 500 × 500 m grid, spread across 14 estates, in February–March 2007.Study and other actions tested
A replicated study in 2007–2009 in six agroforestry sites in Alentejo and Algarve, Portugal (Loureiro et al. 2011) found that European rabbits Oryctolagus cuniculus used most available artificial shelters. European rabbits used 65 out of 100 artificial shelters. Rabbit numbers were higher in areas where a higher percentage of artificial shelters were used (data presented as correlation). Between 2007 and 2009, a total of 100 artificial shelters were constructed across six agroforestry estates dominated by cork oak Quercus suber. Artificial shelters were clustered in groups of 6–8. Each shelter had six entrance points but no more details about shelters were provided. Shelters were surveyed once every three months during the first year after construction and once every six months thereafter. Shelters were considered in use if pellets were detected near their entrances. Rabbit relative abundance was assessed by the density of pellets within a 300-m radius around the shelter.Study and other actions tested
A study in 2007–2009 of a mixed woodland, scrub and agricultural area in southern Portugal (Godinho et al. 2013) found that installing artificial warrens, along with other habitat management, increased presence and abundance of European rabbits Oryctolagus cuniculus. Rabbit presence and abundance were each higher within 100 m of artificial warrens than at greater distances (data reported as statistical model results). Rabbit numbers increased steadily through the study and artificial warrens achieved a 64% occupancy rate by 2009. A range of habitat management actions for rabbits was carried out from 2006 to 2009. These comprised managing scrubland, creating pastures and building 28 artificial warrens (constructed from wood pallets and vegetation remains, covered with soil). Rabbit presence and relative abundance were determined through latrine counts in 45 plots, located around two areas of rabbit activity. Counts were carried out in most months from July 2007 to June 2009.Study and other actions tested
A study in 2004–2013 in a forest reserve in Florida, USA (Cove et al. 2017) found that Key Largo woodrats Neotoma floridana smalli and Key Largo cotton mice Peromyscus gossypinus allapaticola used artificial nest structures. Out of 284 artificial nests, Key Largo woodrats were detected at 65 (23%) and Key Largo cotton mice at 175 (62%). Between 2004 and 2013, over 760 artificial nest structures for woodrats and cotton mice were built in the Crocodile Lake National Wildlife Refuge. Artificial nest structures ranged from boulders and rubble piles to recycled jet-ski structures, cinder blocks with PVC pipes, tin, and natural materials, and 1–2 m segments of plastic culvert pipes cut in half longitudinally and covered in natural materials. In April–May 2013, two hundred and eighty-four artificial nests were monitored using camera traps. One camera trap was set 0.5–3.0 m away from each nest. Cameras recorded for 5–6 nights/nest.Study and other actions tested