Abstract from BTO Research Report No 428:

Newson, S.E. & Noble, D.G.

The production of population trends for UK mammals using BBS mammal data: 1995-2004 update
ISBN No 1-904870-54-6

Executive summary

1. Since 1995, BTO/RSPB/JNCC Breeding Bird Survey (BBS) participants have been voluntarily recording mammals as well as birds on their 1-km squares, making it the first multi-species, annual mammal survey to be carried out in the UK. BBS mammal recording focuses on large-sized easily identifiable species, although observers record any species seen or for which evidence of its presence was found. In this report we update Newson & Noble (2005) to generate estimates of population change for 1995-2004.

2. Annual indices of relative abundance are produced at a national scale for nine mammal species – Brown Hare, Mountain/Irish Hare, Rabbit, Grey Squirrel, Red Fox, Red Deer, Fallow Deer, Roe Deer and Reeves’s Muntjac. Counts of Rabbit, Red Fox, Red Deer and Fallow Deer were significantly lower in 2004 than in 1995, whereas counts of Grey Squirrel were significantly greater. In new work, trends for Fallow and Red Deer are tested for reliability by exploring the effects of a small number of sites with particularly large counts. We recommend that counts from deer parks be excluded from future analyses of deer data.

3. Where data were sufficient, regional indices of relative abundance were produced for English Government Office Regions (GOR) and for the four countries that constitute the UK. Trends could be produced for five mammal species (Brown Hare, Rabbit, Grey Squirrel, Red Fox and Roe Deer) for two or more regions. Additionally, data were sufficient to produce separate trends for Red Deer in Scotland and for Fallow Deer and Reeves’s Muntjac in England.

4. Population trends are produced for Environmental Zones for the most commonly seen species. Environmental Zones are categories of landscapes found in Great Britain from the lowlands of the south and east, to the uplands and mountains of the north and west. The resolution of these analyses is at the 1 km square level, and hence this approach makes results comparable with other mammal surveys associated with the Tracking Mammals Partnership that use the same approach.

5. There are six mammal species (Badger, Mole, Hedgehog, Brown Rat, Stoat and Weasel) for which there were insufficient count data to produce indices of abundance, but for which evidence such as field signs, dead animals or gamekeeper knowledge could be used to record occurrence. These data were used to examine change in presence/absence on BBS squares between 1996 and 2004. We discuss reasons why these trends should be treated with caution. Since 2002 observers have recorded the criteria that they used for assessing presence (live animals, field signs, dead animals, local knowledge of presence from that season or live animals seen on additional visits), which should aid interpretation in the future.

6. Data for species seldom detected by sight or other evidence provide important information on their distribution. There is also the potential for combining these data with those from other surveys and with records in the National Biodiversity Network to provide a better understanding of changes in distribution over time.

Back to Research Reports 345 onwards