Release translocated/captive-bred mammals at a specific time (e.g. season, day/night)

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Seven studies evaluated the effects of releasing translocated or captive-bred mammals at a specific time (season or day/night). Three studies were in the USA and one each was in the UK, Canada, Ireland and Hungary.



  • Survival (7 studies): Four of five studies in the UK, Canada and the USA found that translocated common dormice, black bears and Canadian lynx and captive-bred swift foxes released in a specific season had higher survival rates than those released during another season. The other study found that red squirrels translocated in autumn and winter had similar survival rates. A randomised, replicated, controlled study in Hungary found that translocated European ground squirrels released during the morning had higher recapture rates than those released during the afternoon. A study in the USA found that most translocated kangaroo rats released at dusk in artificial burrows supplied with food died within five days of release.
  • Condition (1 study): A study in the UK found that common dormice translocated during summer lost less weight than those translocated during spring.


  • Behaviour change (2 studies): Two studies in the UK and USA found that common dormice translocated during spring and black bears translocated during winter travelled shorter distances or settled closer to the release site than those translocated during summer.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A study in 1991–1992 in a woodland reserve in Somerset, UK (Bright & Morris 1994) found that common dormice Muscardinus avellanarius translocated during spring had lower survival rates, lost more weight and travelled shorter distances than dormice translocated during summer. Overall, five of seven dormice (57%) released in spring survived the first 10 days post release compared to seven of eight (80%) dormice released in summer. Common dormice translocated in spring lost more weight (0.30 g/day) than did dormice translocated in summer (0.14 g/day). However, they moved shorter daily distances from their release site (spring translocation: 119 m/day; summer translocation: 292 m/day). Seven dormice were translocated in spring (between 30 May and 28 June 1991) and 10 in summer (between 24 August and 30 September 1992) to a 9-ha strip of woodland and scrub. Dormice were caught during the morning, moved to the release site and placed there by early afternoon, in the nestbox in which they had been captured. Individuals were fitted with radio-transmitters and followed for 10–20 nights. Dormice were weighed until 10–14 days after release.

    Study and other actions tested
  2. A replicated, controlled study in 1987–1991 in three grassland sites in Alberta, Canada (Carbyn et al. 1994) found that, after one year, survival of captive-bred swift foxes Vulpes velox released in autumn was greater than that of captive-bred swift foxes released in spring. No statistical analyses were performed. At least 10 out of 71 (14%) swift foxes released in autumn survived over one year post-release, compared with at least one out of 27 (4%) of those released in spring. Eighty-one captive-born swift foxes were released in autumn and 41 were released in spring. They were provided with supplementary food for 1–8 months. Swift foxes were radio-collared and 98 were monitored from the ground and air for over one year.

    Study and other actions tested
  3. A study in 1995–1999 in a forested area of Kentucky and Tennessee, USA (Eastridge & Clark 2001) found that black bears Ursus americanus translocated during winter had higher survival rates and settled closer to the release area than did bears translocated in summer. First-year post-release survival of winter-released bears (88%) was higher than that of summer-released bears (20%). Winter-released bears remained closer to release sites during the two weeks after emergence from dens (0.4–3.6 km) than did summer-released bears during the two weeks after release (1.1–15.8 km). Eight adult female bears (five with 13 cubs in total and three assumed to be pregnant) were translocated to artificial dens in a 780-km2 study area in January–March 1996 and March 1997. Six adult female bears were released in June–August 1996, following two weeks in acclimation pens at release sites. Bears were radio-tracked daily on release, reducing gradually to twice/week, until December 1999. Post-release survival was calculated with emigration included within mortality.

    Study and other actions tested
  4. A study in 2005–2007 in a mixed conifer forest in Galway, Ireland (Poole & Lawton 2009) found that red squirrels Sciurus vulgaris translocated in September and October had similar survival rates compared to squirrels translocated in December. The survival rate to the following May of red squirrels translocated in September and October (78%, 7/9 individuals) was not statistically different to that of squirrels released in December (50%, 5/10 individuals). In August 2006, seven juvenile squirrels were caught and at least one squirrel was still alive in the release location two years after the original release. Nineteen squirrels were translocated to a nature reserve (19 ha) in the middle of a 789-ha commercial pine plantation, 112 km from the capture site. Squirrels were kept for an average of 46 days in one of two pre-release enclosures (3.6 × 3.6 × 3.9 m high). Enclosures contained branches, platforms, nest boxes, and supplementary feeders. Food and nest boxes were also provided in the periphery of the release site. Nine squirrels were released in September or October 2005 and 10 in December 2005. Squirrels were radio-tracked in September and November 2005 and February and May 2006, and were trapped in February, May and August 2006 and observed once in October 2007.

    Study and other actions tested
  5. A study in 2001 in a grassland and shrubland site in California, USA (Germano 2010) found that most translocated Tipton kangaroo rats Dipodomys nitratoides nitratoides and Heermann’s kangaroo rats Dipodomys heermanni ssp. released at dusk in artificial burrows supplied with food died within five days of release. All four Tipton kangaroo rats were predated within five days of translocation, and only one out of seven Heermann’s kangaroo rats survived over 45 days. Three Heermann’s kangaroo rats were predated, two died as a result of aggression from other kangaroo rats, and the fate of one was unknown. In September 2001, four juvenile Tipton kangaroo rats and three Heermann’s kangaroo rats were captured and held in captivity for two months before release at a protected site in November. In December 2001, a further four Heermann’s kangaroo rats were caught and translocated to the same site. All 11 animals were fitted with a radio-transmitter and ear tags, and monitored for seven days in captivity prior to release. The release site was already occupied by Heermann’s kangaroo rats. Animals were released into individual artificial burrows (two 90-cm-long cardboard tubes with a chamber about 30 cm below the surface), dug 10–15 m apart and provided with a paper towel and seeds. Burrows were plugged with paper towels until dusk. Animals were radio-tracked every 1–8 days for 18–45 days after release.

    Study and other actions tested
  6. A study in 1999-2007 in montane forest in Colorado, USA (Devineau et al. 2011) found that translocated Canadian lynx Lynx canadensis held in captivity and released in spring had higher survival rates in the first year than those released at other times of year. Lynx released in spring after >45 days in captivity near the release location had lower monthly mortality rates (0.4-2.8% in 2000-2006) than lynx held for up to seven days in captivity near the release location (20.5% in 1999) and not released in spring. Overall, 117 of 218 released lynxes (53%) survived to at least 1–8 years after release. From 1999 to 2006, two hundred and eighteen lynx were translocated to Colorado from Canada and USA. Lynx were held in captivity near their source location (for 3-68 days) prior to transfer to a holding facility (with 40 x 2.4 x 1.2 m pens with ceilings) in Colorado (100 km from release site). Time in the Colorado holding facility varied (5-137 days): release within seven days following veterinary inspection (4 individuals in 1999); release after 3 weeks (9 individuals in 2000); release after >3 weeks in the spring (1 April-31 May; 28 individuals in 2000); release in spring after >3 weeks in captivity but excluding any juvenile females or pregnant females (177 individuals in 2000-2006). Lynx were fed a diet of rabbit and commercial carnivore food while in captivity. Lynx were monitored for the first year following release using radio-telemetry (1,878 locations/month recorded).

    Study and other actions tested
  7. A randomised, replicated, controlled study in 2000 in a grassland site in central Hungary (Gedeon et al. 2011) found that translocated European ground squirrels Spermophilus citellus released during the morning had higher recapture rates than ground squirrels released during the afternoon. From four to 10 days after release, a higher proportion of ground squirrels that had been released in the morning were recaptured (18 out of 58, 29%) than those released in the afternoon (7 out of 59, 12%). The highest recapture rate came from the group released in the morning in to plugged burrows (15 out of 30, 50%). From 22–24 April 2000, one hundred and seventeen wild-caught European ground squirrels were translocated to a fenced 40-ha protected grassland. Four 40 × 40-m grid cells were established, each containing vertical, artificial burrows (50 cm long, 4.5 cm diameter) spaced 4.5 m apart. Fifty-nine animals were released into burrows in two grid cells during the afternoon on the day of capture and 58 into burrows in the other two grid cells the morning after capture. Animals to be released in the morning were kept in individual wire cages (10 × 10 × 40 cm) for one night and provided with fresh apple slices prior to release. One individual was released/burrow. Approximately half the burrows for each release group were plugged with wood caps so that squirrels could only exit by digging out. From 28 April–2 May, squirrels were recaptured with snares.

    Study and other actions tested
Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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Terrestrial Mammal Conservation

This Action forms part of the Action Synopsis:

Terrestrial Mammal Conservation
Terrestrial Mammal Conservation

Terrestrial Mammal Conservation - Published 2020

Terrestrial Mammal Conservation

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