Translocate mammals to reduce overpopulation

Overall effectiveness category Trade-off between benefit and harms
Number of studies: 3
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How is the evidence assessed?

Effectiveness

66%
Certainty

47%
Harms

20%

Calculating overall effectiveness category

Background information and definitions

Overpopulation can reduce the long-term persistence of a population, as competition for resources increases. Translocating individuals of the target species away from the area or predators into the area for example, to reduce population numbers may help reduce competition for resources and thus improve the fitness of the remaining population.

Study locations

Key messages

Three studies evaluated the effects of translocating mammals to reduce overpopulation. Two studies were in the USA and one was in Australia_.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (3 STUDIES)

Abundance (1 study): A before-and-after study in the USA found that adult elk numbers approximately halved after the translocation of wolves to the reserve.
Reproductive success (1 study): A before-and-after study in the USA found that elk calf:cow ratios approximately halved after the translocation of wolves to the reserve.
Survival (2 studies): A study in Australia found that koalas translocated to reduce overpopulation had lower survival than individuals in the source population. A study in the USA found that following translocation to reduce over-abundance, white-tailed deer had lower survival rates compared to non-translocated deer at the recipient site.
Occupancy/range (1 study): A study in the USA found that following translocation to reduce over-abundance at the source site, white-tailed deer had similar home range sizes compared to non-translocated deer at the recipient site.

BEHAVIOUR (0 STUDIES)

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

A study in 1993–1995 in a forest reserve in New York, USA (Jones et al. 1997) found that following translocation to reduce over-abundance at the source site, white-tailed deer Odocoileus virginianus had lower survival rates but similar home range sizes compared to non-translocated deer at the recipient site. One year after release, the annual survival rate for translocated deer (53%) was lower than that of non-translocated deer at the recipient site (75–88%). During the year after release, average home range sizes did not differ significantly between translocated deer (0.23 km²) and non-translocated deer at the recipient site (0.22 km²). In May–June 1994, seventeen female white-tailed deer were translocated from an over-populated site to a site 60 km away. In April–July of 1993–1995, twenty deer resident at the recipient site (16 females, 4 males) were captured. All deer were radio-collared. Before release, deer were held for 1–12 days in a 50-m² pen. Deer were monitored using radio-telemetry, 5–15 times/week, in April–August of 1993–1995, and less frequently at other times of the year.
Study and other actions tested
Referenced paper
Jones M.L., Mathews N.E. & Porter W.F. (1997) Influence of social organization on dispersal and survival of translocated female white-tailed deer. Wildlife Society Bulletin, 25, 272-278.
A before-and-after study in 1986–2004 in a grassland and forest reserve in Wyoming, USA (White & Garrott 2005) found that adult elk Cervus canadensis numbers and elk calf:cow ratios approximately halved after the translocation of wolves Canis lupus to the reserve. Results were not subject to statistical analysis. Nine years after wolves were translocated, there were fewer adult elk (8,335) and a lower calf:cow ratio (12 calves/100 female elk) than the average before wolf translocation (adult elk: 16,664; 25 calves/100 female elk). A similar number of elk that had migrated out of the park were killed by hunters before (1,148 elk/year) and after (1,297 elk/year) wolves were translocated. Wolves were translocated into Yellowstone National Park in 1995. Between 1996 and 2004 wolf numbers increased from 21 to 106. Elk adults and calves were counted from aeroplanes annually during December–January 1986–2004. No counts were conducted during the winters of 1996 and 1997.
Study and other actions tested
Referenced paper
White P.J. & Garrott R.A. (2005) Northern Yellowstone elk after wolf restoration. Wildlife Society Bulletin, 33, 942-955.
A study in 2007–2008 of forest sites on an island and the mainland of southeastern Australia (Whisson et al. 2012) found that koalas Phascolarctos cinereusi translocated to reduce overpopulation had higher mortality than individuals in the source population. Six of 16 koalas (38%) that were sterilized and translocated died within 12 months of release, whereas none of 13 koalas in the source population died within the same time period. In April–May 2007, sixteen koalas (eight females; eight males) were surgically sterilized and translocated from an overpopulated island to the mainland. Release sites were 10-ha forest blocks dominated by rough-barked manna gum Eucalyptus viminalis. Released koalas were radio-collared and tracked daily for one week followed by weekly for seven weeks and monthly until June 2008. Thirteen unsterilized koalas (eight females; five males) belonging to the source population were radio-collared and tracked over the same period in 2007–2008.
Study and other actions tested
Referenced paper
Whisson D.A., Holland G.J. & Carlyon K. (2012) Translocation of overabundant species: implications for translocated individuals. Journal of Wildlife Management, 76, 1661-1669.

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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This Action forms part of the Action Synopsis:

Terrestrial Mammal Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Airborne translocation of mammals using parachutes Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Use holding pens at release site prior to release of translocated mammals Action Link	Likely to be beneficial	35	Synopsis Link
Release translocated mammals into fenced areas Action Link	Beneficial	24	Synopsis Link