GWCT National Gamebag Census & Tracking Mammals Partnership

Brown rat Rattus norvegicus

Taxonomy: Class: Mammalia; Order: Rodentia; Family: Muridae

Description

Brown rat photo
Brown rat © Peter Thompson

The brown rat, also known as the common or Norway rat, is thought to originate from central Asia. Highly adaptable and long associated with man's activities, it spread across Europe and into Britain in the 18th century, largely displacing the black rat (also called ship rat) that had been present since Roman times. It is a pest of stored food, a vector of human diseases and a predator of birds' eggs and chicks.

Rat control may take place at any time of year. Since the Second World War, poison became the favoured means of control, with the consequence that most rats die underground and their numbers are not reported. NGC returns are thus underestimates, and refer mainly to rats shot or caught in tunnel traps. They also do not include urban rats, so trends should be interpreted with caution.

Further information:
Mammal Society website brown rat page.

Conservation status and legislation

Status:
UK: Non-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 brown rat occurs throughout Britain and on all offshore islands except for a few of its smallest ones. It is least common in exposed upland areas. It also occupies the whole of Ireland, despite the paucity of records on the map.

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

United Kingdom 6,790,000
England 5,240,000
Scotland 870,000
Wales 680,000
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.

Brown rat trend United Kingdom

The bag index was broadly stable until the 1990s, when it began to increase. Overall, this means that the bag index has doubled between 1961 and 2009. The increase matches the widespread perception that rats have been much more numerous recently, and it is possible that a series of mild winters boosted survival.

Change in brown rat 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 940 1961 2009 95*
33 to 164
89*
46 to 150
112*
56 to 190

* 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.

Brown rat trend England

The bag index was broadly stable until the 1990s, when it began to increase. Overall, this means that the bag index has doubled between 1961 and 2009. The increase matches the widespread perception that rats have been much more numerous recently, and it is possible that a series of mild winters boosted survival.

Change in brown rat 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 720 1961 2009 104*
35 to 191
97*
50 to 174
130*
56 to 214

* 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.

Brown rat trend Scotland

The bag index has doubled between 1961 and 2009, but the error bars on the estimated values are so large that it is not possilbe to detect a significant change. The apparent increase matches the widespread perception that rats have been much more numerous recently, and it is possible that a series of mild winters boosted survival.

Change in brown rat 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 178 1961 2009 110
-26 to 511
36
-31 to 174
4
-39 to 76

* 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.

Brown rat trend Wales

Since the start of the series, the bag index declined steadily until the 1990s. As a result, there has been an overall significant decline between 1961 and 2009. It is not known why the trend is so different from that in other parts of the country.

Change in brown rat 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 30 1961 2009 -81*
-93 to -39
-51
-81 to 44
7
-60 to 61

* significant at P < 0.05

N Ireland

There are too few bag records of brown rat to produce an index graph. Brown rat trend N Ireland

 

There are too few bag records of brown rat 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 brown rat 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) 458 1961 2009 105*
37 to 197
91*
45 to 195
127*
47 to 228
Westerly lowlands (England/Wales) 191 1961 2009 33
-55 to 108
34
-45 to 170
56
-28 to 190
Uplands (England/Wales) 93 1995 2009 no data no data 318*
168 to 553
Lowlands (Scotland) 59 1961 2009 137
-51 to 1047
-11
-68 to 112
-35
-75 to 54
Intermediate uplands/islands (Scotland) 34 1961 2009 3
-43 to 75
11
-36 to 114
54
-16 to 172
True uplands (Scotland) 87 1961 2009 -13
-71 to 129
40
-46 to 298
16
-41 to 212

* significant at P < 0.05

Comparison with BBS mammal data

No comparison with the NGC trend is possible because too few brown rat 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 brown rat 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.
  • Hart,M. (1982). Rats. Allison & Busby, London.
  • Meehan,A.P. (1984). Rats and Mice: Their Biology and Control. Rentokil, East Grinstead.
  • Twigg,G.L. (1975). The Brown Rat. David & Charles, London.

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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