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Effects of agricultural management on farmland birds - BD0901

Substantial declines in population abundance and distribution of farmland birds have been identified by the British Trust for Ornithology (BTO) from data collected in the Common Bird Census (CBC) and through reference to atlases of breeding bird distributions. This study will aim to investigate the effects of a range of farming practices on changes in population size and range for a selected range of bird species typical of farmland habitats. The study will be composed of 6 specific objectives outlined as follows, together with ways in which they might be achieved: 1. Analysis of CBC, atlas and BTO rook survey data sets to produce regional population indices and regional changes in distribution for 19 bird species (including kestrel, turtle dove, whitethroat, song thrush, yellowhammer and corn bunting) typical of farmland habitats over the past 20-30 years. This work will be largely focused on lowland agriculture in the lower half of mainland Britain; counties within this area will be classified as intensive or non-intensive lowland agriculture and multivariate analysis will be used to define different regions (probably counties) in terms of agricultural change over the last 20 years. Bird population statistics will be calculated for each region using appropriate statistical techniques and by assessing changes between 2 atlas periods (1968-72 and 1988-91); 2. Collection of regional agricultural practice data for the last 20 years for a range of activities likely to affect bird populations, such as spring vs. autumn sowing of cereals, simplification of crop rotation, intensified grassland management and use of pesticides. Results from the ITE Countryside Survey and other studies will be collated in order to identify trends that can be linked to bird population changes; 3. Collection of new breeding population data in 1996 and 1997 for approximately 50 farms previously monitored for bird populations (CBC) in the period 1965-1975. Where possible, data will be collected from volunteers who originally carried out the CBC for that particular farm; in other farms, contract fieldworkers will carry out the CBC. Territory mapping methods able to permit valid comparisons with the earlier censuses will be used; 4. Collection of broad agricultural practice data for at least the last 20 years from the study farms by means of farm visits and the use of questionnaires compiled by experienced farm data collectors; 5. Analysis of the databases collated in objectives 1-4 in order to investigate whether changes in agricultural practices coincide with changes in population size and distribution of the selected bird species at farm, regional and national scales. Formal statistical analyses will be used to identify changes in agricultural practices which individually, or in combination with others, best fit observed changes in bird populations. Relationships between CBC indices and annual agricultural statistics will be examined using appropriate time-series techniques in order to determine models providing the best fit to the data. Using farm questionnaire data, each farm will be classified in terms of the types of agricultural change that have occurred over the last 30 years, and population changes will be compared between different categories of farms; and 6. Assessment of whether changes in bird populations associated with pesticide use have been caused by direct toxicity or other mechanisms (such as reduced food availability or nesting sites). This will be conducted using an approach developed by CSL for a recent cost-benefit analysis of pesticide usage. Toxicity data and application rates for pesticides will be compared using established risk assessment methods to assess whether direct toxic effects on birds were likely to have occurred. Similar methods will be used to assess toxic effects on insects and plants. Simple ecological models will then be used to assess the relative contribution of direct and indirect toxicity effects to the decline in farmland bird populations.
Time-Scale and Cost
From: 1995

To: 1998

Cost: £228,556
Contractor / Funded Organisations
British Trust For Ornithology
Fields of Study
Environmental Stewardship