Description:

This indicator describes changes in the numbers of breeding birds in Scotland. Birds can respond relatively quickly to variations in habitat extent and quality through changes in breeding output, survival or dispersal. Since most widespread and abundant bird species are relatively easy to identify and count, they are often used as indicators of environmental change.

With this indicator, it is used as a proxy measure of biodiversity, as biodiversity cannot be measured by a single indicator.

Source of Data:

Terrestrial breeding birds are recorded primarily through the Breeding Bird Survey (BBS).

Data are supplied by British Trust for Ornithology and Royal Society for Protection of Birds to Scottish Natural Heritage (SNH) under contract. This is an Official Statistic produced by SNH.

The Terrestrial Breeding Bird index is published by SNH, future updates are planned to be available annually every November (data are 11 months in arrears). The summarised data that are used to produce the index are available on SNH's website.
SNH's website.

Since 1994 the BBS has recorded population estimates of birds in Scotland based on a random sample of 1 km Ordnance Survey grid squares which are representative of the main terrestrial habitats. Two visits are made to each 1 km square during the breeding season (April to July). There are 66 species included in the indicator; 10 of these species are assessed using targeted surveys as they are too scarce to be monitored by the BBS or are better monitored through specialist surveys.

A further 46 scarce terrestrial species regularly breed in Scotland but insufficient data are available to permit inclusion in these indicators.

The methodology for constructing the index is to determine the species for which there are suitable data available (in this case species which are present in 30 or more 1 km squares). The geometric mean index of change is calculated based on all of the individual species trends. 

The methods are described fully in SNH Commissioned Research Report 245 (which can be found here) and also from information on methodology..

Definitions:

Index of abundance is an index which combines information on the numbers of selected species, rather than their spatial coverage.

Terrestrial breeding birds in Scotland comprise of resident and migratory species. They include familiar garden species such as blackbird (Turdus merula) and robin (Erithacus rubecula), woodland species such as willow warbler (Phylloscopus trochilus) and goldcrest (Regulus regulus), farmland species such as linnet (Carduelis cannabina) and goldfinch (Carduelis carduelis), and bird species found in the uplands such as raven (Corvus corax) and black grouse (Tetrao tetrix).

Criteria for Change:

This evaluation is based on: any difference in the index within +/- 3 points of last year's figure suggests that the position is more likely to be maintaining than showing any change. An increase of 3 index points or more suggests the position is improving; whereas a decrease of 3 index points or more suggests the position is worsening.