GWCT National Gamebag Census & Tracking Mammals Partnership

Weasel Mustela nivalis

Taxonomy: Class: Mammalia; Order: Carnivora; Family: Mustelidae

Description

Weasel photo
Weasel © Laurie Campbell

The weasel is Britain's smallest native carnivore. It has a long slender body and a short tail that, unlike a stoat's tail, lacks a black tip. It feeds mainly on small rodents, and flourished when the arrival of myxomatosis led to a much reduced rabbit grazing pressure that benefited voles and mice. It also commonly eats birds and their eggs and chicks, including those of gamebirds. The weasel may be culled throughout the year.

Further information:
Mammal Society website weasel page.

Conservation status and legislation

Status:
UK: Native
World: Least Concern (IUCN Red List)

Legislation:
 
Logo NBN Gateway © Crown Copyright. All rights reserved NERC 100017897 2004
Source: National Biodiversity Network and its data providers, who bear
no responsibility for interpretation of the 10x10-km grid map
 

Distribution and abundance

The weasel lives throughout mainland Britain. It is present on the Isle of Sheppey, Isle of Wight, Anglesey and the Scottish islands of Skye and Bute. It is absent from Ireland, the Isle of Man and the Channel Islands.

Estimates of weasel abundance (numbers of individuals in the spring) across the UK, from Harris et al. (1995):

United Kingdom 450,000
England 308,000
Scotland 106,000
Wales 36,000
N Ireland no estimate

Recent trends from the National Gamebag Census

United Kingdom

Index of bag density from 1961 to 2009 (see statistical methods and interpretational considerations).
Error bars represent 95% confidence intervals.

Weasel trend United Kingdom

The bag index more than halved between 1961 and the late 1980s/early 1990s. Since then there has been a significant increase, resulting in an overall decline of about a third between 1961 and 2009. The pattern of change is the opposite of that for rabbit, so may be associated with the negative effect of rabbit grazing on vole abundance.

Change in weasel bags over time, with 95% confidence limits (see statistical methods):

Country Sites Start
year
End
year
Change (%)
1961-2009
Change (%)
1984-2009
Change (%)
1995-2009
United Kingdom 1006 1961 2009 -37*
-52 to -22
39*
9 to 70
51*
23 to 80

* significant at P < 0.05

England

Index of bag density from 1961 to 2009 (see statistical methods and interpretational considerations).
Error bars represent 95% confidence intervals.

Weasel trend England

The bag index more than halved between 1961 and the late 1980s/early 1990s. Since then there has been a significant increase, resulting in an overall decline of about a third between 1961 and 2009. The pattern of change is broadly the opposite of that for rabbit, so may be associated with the negative effect of rabbit grazing on vole abundance.

Change in weasel bags over time, with 95% confidence limits (see statistical methods):

Country Sites Start
year
End
year
Change (%)
1961-2009
Change (%)
1984-2009
Change (%)
1995-2009
England 735 1961 2009 -37*
-53 to -19
53*
9 to 104
73*
31 to 122

* significant at P < 0.05

Scotland

Index of bag density from 1961 to 2009 (see statistical methods and interpretational considerations).
Error bars represent 95% confidence intervals.

Weasel trend Scotland

There has been no detectable change in the bag index between 1961 and 2009.

Change in weasel bags over time, with 95% confidence limits (see statistical methods):

Country Sites Start
year
End
year
Change (%)
1961-2009
Change (%)
1984-2009
Change (%)
1995-2009
Scotland 242 1961 2009 -16
-43 to 32
17
-17 to 65
23
-4 to 55

* significant at P < 0.05

Wales

Index of bag density from 1961 to 2009 (see statistical methods and interpretational considerations).
Error bars represent 95% confidence intervals.

Weasel trend Wales

There has been an apparent decline in the bag index between 1961 and 2009, but it is not statistically significant. The apparent pattern is the opposite of that for rabbit, so may be associated with the negative effect of rabbit grazing on vole abundance.

Change in weasel bags over time, with 95% confidence limits (see statistical methods):

Country Sites Start
year
End
year
Change (%)
1961-2009
Change (%)
1984-2009
Change (%)
1995-2009
Wales 28 1961 2009 -93
-96 to 25
-75
-88 to 16
-67
-85 to 41

* significant at P < 0.05

N Ireland

There are too few bag records of weasel to produce an index graph. Weasel trend N Ireland

 

There are too few bag records of weasel to evaluate rates of change over time

Country Sites Start
year
End
year
Change (%)
1961-2009
Change (%)
1984-2009
Change (%)
1995-2009
N Ireland Too few sites

Environmental zones

Change in weasel bags over time, with 95% confidence limits (see statistical methods):

Environmental zone Sites Start
year
End
year
Change (%)
1961-2009
Change (%)
1984-2009
Change (%)
1995-2009
Easterly lowlands (England/Wales) 476 1961 2009 -70*
-80 to -59
-35*
-55 to -16
-18
-41 to 5
Westerly lowlands (England/Wales) 181 1961 2009 -67*
-81 to -45
-32
-58 to 6
-6
-40 to 37
Uplands (England/Wales) 102 1961 2009 16
-58 to 758
311*
166 to 537
204*
131 to 307
Lowlands (Scotland) 71 1961 2009 -64*
-86 to -7
-47
-72 to 3
-38
-67 to 9
Intermediate uplands/islands (Scotland) 34 1961 2009 -81*
-89 to -50
-40
-66 to 71
-26
-57 to 57
True uplands (Scotland) 137 1961 2009 37
-22 to 127
53*
3 to 168
52*
12 to 109

* significant at P < 0.05

Comparison with BBS mammal data

No comparison with the NGC trend is possible because too few weasel records are received through the Breeding Bird Survey (BBS) organised by the British Trust for Ornithology.

Long-term trend from the National Gamebag Census

There are too few bag records of weasel to produce a trend starting before 1961.

References and further reading

  • Battersby,J. (2005). UK Mammals: Species Status and Population Trends. Joint Nature Conservation Committee/Tracking Mammals Partnership, Peterborough (JNCC download page).
  • Harris,S., Morris,P., Wray,S. & Yalden,D.W. (1995). A Review of British Mammals: Population Estimates and Conservation Status of British Mammals Other than Cetaceans. Joint Nature Conservation Committee, Peterborough (JNCC download page).
  • Harris,S. & Yalden,D.W. (2008). Mammals of the British Isles: Handbook, 4th edition. Mammal Society, Southampton.
  • McDonald,R. & Harris,S. (2006). Stoats and Weasels. Mammal Society, Southampton.
  • Sheffield,S.R. & King,C.M. (1994). Mustela nivalis. Mammalian Species 454: 1-10.

This report should be cited as: Aebischer,N.J., Davey,P.D. & Kingdon,N.G. (2011). National Gamebag Census: Mammal Trends to 2009. Game & Wildlife Conservation Trust, Fordingbridge (http://www.gwct.org.uk/ngcmammals).

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