Developing bird indicators
Indicator Update – January 2011
The latest wild bird indicators were published this week, based largely on the updated population trends of birds monitored through the BTO’s major schemes such as BBS and WeBS. Two sets were published simultaneously: the UK Biodiversity Indicators and the England Biodiversity Strategy indicators which are based solely on English trends. All indicators for terrestrial habitats (farmland, woodland, wetlands and waterways) showed a marked downward drop in 2009, reflecting in part the effects of the cold 2008-09 winter, its effects most evident for species such as Stonechat and Goldcrest. However, individual species within these indicators show variable patterns, with farmland specialists such as Turtle Dove and Starling, and woodland specialists such as Willow Tit continuing to decline, while species such as Goldfinch and Blackcap increased. Overall, numbers of wintering waders and wildfowl also fell between 2007/08 and 2008/09, continuing a decline evident since their peak numbers in the early 1990s. Amongst this group, species such as European White-fronted Geese, Pochard, Dunlin and Ringed Plover show marked declines, whereas numbers of wintering Whooper Swan, Pink-footed Goose and Avocet have increased dramatically. The breeding seabird index increased slightly in 2009, but remains below its peak value in the late 1990s, due to continuing declines in species such as Kittiwake and Arctic Skua.
Figure 1. UK Biodiversity Indicator: populations of wild birds, 1970 to 2009
Figure 2. UK Biodiversity Indicator: populations of wintering waterbirds, 1975/6 to 2008/9
Developing bird indicators
UK Bird Indicator
In the UK, there has been considerable development in the use of wild bird indicators as proxies for the health of wildlife in the wider countryside, most using the approach of a composite indicator composed of population trends of species grouped by geographic region or ecological associations. The best example is the UK Sustainable Development Strategy indicator reported annually showing patterns of change in farmland, woodland, wetland and marine/coastal birds, but similar indicators are produced annually for England and its regions, Scotland and Wales. The concept behind using populations of common birds as indicators of the state of the environment is based on the assumption that there will be commonalities in the spatial and temporal patterns of abundance among different taxa and in their responses to major environmental drivers. Birds are considered to be particularly useful because they occupy a wide range of habitats, tend to be near the top of the food chain, have a high public profile, their ecology is relatively well understood, and long-term data are readily available. However, despite some evidence of correlations, the extent to which birds can be used as proxies for other taxa is an interesting issue, currently being further explored under a number of research initiatives at the BTO.
Wild bird indicators in the UK were first developed by the BTO and RSPB in 1999, using an approach of combining measures of population change for as many species as possible in a composite index, categorised by broad habitat groupings (e.g. farmland, woodland, coastal, urban). Sources of data varied, but most are generated from two of the BTO’s major monitoring schemes – the Breeding Bird Survey for terrestrial species, and the Wetland Bird Survey for wintering waterbirds.
The original bird indicator, was adopted and published by Defra in 2000, as part of a suite of 15 headline Quality of Life indicators alongside measures of human health, education standards and housing, and continues to be used today. Importantly, the UK government adopted a Public Service Agreement (PSA) target in 2002 to reverse the long-term decline in farmland birds by 2020, as measured by this index, and to be assessed in annual updates. Secondly, the woodland index was adopted by the Forestry Commission as an index of sustainable forestry. Since then, there has been a proliferation of indicators developed for geographical regions within the UK. In Scotland, there are three annually updated Scottish Natural Heritage biodiversity indicators based on bird populations: one for terrestrial breeding birds that shows trends in farmland, woodland and upland bird populations, one for wintering waterbirds, and one for seabirds. In England, indicators for the England Biodiversity Strategy are produced annually for five landscape themes; farmland, woodland, urban, wetlands and waterways, coastal and marine, based on population trends since 1970. We also analyse BBS data since 1994 to produce shorter-term largely terrestrial regional bird indicators for England’s nine government office regions (North West, North East, Yorkshire and Humberside, East Midlands, West Midlands, East of England, South East, South West and London) which illustrate a south-north gradient in the magnitude of declines in both farmland and woodland species over this period.