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Accelerating declines
revealed by new BTO report

The latest report of trends from the BTO's monitoring schemes has just been published - but this time on the Web www.bto.org/birdtrends. It brings together information from BBS, CBC, WBS, NRS and CES to provide a detailed picture for over 100 species of landbirds.

A new system of Alerts has also been introduced, to highlight where population declines of greater than 25% or greater than 50% have occurred over the past 5, 10, 25 and 30 years. This is the new standard system that has been widely discussed with those concerned with bird population monitoring and that we hope will be extended to other bird monitoring schemes in due course.

Winners and losers

While many species show relatively small long-term trends or may vary up-and-down with changes in the weather, for example, there are a substantial proportion that have shown large long-term trends (Table1). Thus 12 species have more than doubled in population size over the past 25 years, while 22 have halved.

The "winners" include species such as the raptors, which have benefited from conservation action to curb the use of damaging pesticides.

Mute Swan has benefited substantially from banning the use of lead weights by fishermen.

The pigeons appear to have taken advantage of various changes in agricultural practice, including the increase in brassicas such as oilseed rape and may be benefiting from climate warming through increased breeding season length and perhaps decreases in over-wintering mortality.

The reasons for increases in the warblers, Redstart and Nuthatch are currently unknown, but the last has been spreading northwards into Scotland at a remarkable rate.

The species that have declined by greater than 50% or 25% over the past 25 years are largely unchanged since the previous reports (Table 1). The only differences are that Yellow Wagtail, Marsh Tit, Starling and Linnet have now moved onto the higher level of decline, and the declines for Kestrel and Cuckoo are now greater than 25%.

Little Grebe is a new species to the list of declining species and needs further investigation. Although winter surveys show no trend over the past 15 years, the decline measured by the Waterways Bird Survey occurred mainly before this period and represents changes only in the numbers of grebes using rivers and canals, not lakes, gravel pits or reservoirs.

Declining faster and faster

What is most worrying about the new report is that eight of the species in Table 1 appear to have declined faster than ever over the last 5 years on CBC plots. They show declines greater than 25% between just 1993 and 1998: Grey Partridge, Lesser Spotted Woodpecker, Tree Pipit, Yellow Wagtail, Willow Tit, Starling, Tree Sparrow and Lesser Redpoll.

The quality of information for some of these species is often unsatisfactory because they now occur on very few CBC plots, although the recent declines are confirmed by significant BBS results for Grey Partridge, Tree Pipit in England, Yellow Wagtail and Willow Tit. The general lack of information on these species combined with evidence of rapid declines means that they surely warrant urgent conservation attention. For two other species on Table 1, Bullfinch and Corn Bunting, BBS shows significant declines of greater than 25% between 1994 and 1999 - see BTO News 230: 12-14.

Conservation planning

BTO data have been very important in helping government draw up lists of priority species needing conservation action. Under the International Convention on Biodiversity, the government has produced a series of Biodiversity Action Plans for individual species and habitats. These plans list the main factors that may be causing population declines in each species, suggest policies to halt and reverse declines and outline what further research is still required. Following their publication, there has been much new action at national and local levels to conserve the UK's biodiversity.

Grey Partridge was one of the first species with an Action Plan and has been the subject of intense research work for many years by the Game Conservancy Trust. Based on all available evidence, GCT has made strong recommendations about how the species' fortunes can be turned around, principally to do with the provision of chick food - insect larvae - that have all but disappeared with the use of insecticides and of herbicides that kill the weeds the insects feed on. However, it looks as though there is still a great deal of work to do to achieve the stated aim of halting its population decline by 2005.

Tree Sparrow, Bullfinch and Corn Bunting are also the subjects of Biodiversity Action Plans as well as of a number of research projects and conservation initiatives by BTO, GCT, RSPB and others. These have highlighted the potential importance of investigating the impact of providing extra seed in winter, to make up for the loss of natural food supplies due to widespread changes in farming practice. All three Action Plans aim to achieve at least a 50% increase in the BBS index of each species between 1996 and 2008.

The UK government, through the Department of the Environment, Transport & the Regions, has recently funded a consortium led by the BTO (including Central Science Laboratory, RSPB and Wildwings Consultants) to investigate the causes of the long-term declines of Starling (and House Sparrow).

Also the BTO, through its Nightingale Appeal and with support under the BTO/JNCC Partnership has funded an investigation of the BTO's data on Willow and Marsh Tits.

However, there is now an obvious need for research to begin on the declines of Lesser Spotted Woodpecker, Tree Pipit, Yellow Wagtail and Lesser Redpoll before they disappear from large parts of the country.

Table 1: Species showing population declines of greater than 50% or 25% over the past 25 years (1973-1998); the percentage declines for each species is given in parentheses), each decline is statistically significant. Please note that although we use data from the most recently processed year, 1999, in the analysis, statistical considerations requires the changes to be measured only up to 1998.

N.B. It should be emphasised that these alerts do not result in any immediate changes to existing lists, such as the Biodiversity Steering Group and Birds of Conservation Concern lists, but they flag up those species that are most in trouble and that may warrant redesignation (currently under way).

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