Weasel Mustela nivalis

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

Description

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)

© 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

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.

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.

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.

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.

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.

 

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):

* 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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