monitoring breeding birds in the united kingdom - European Bird ...

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The scope of monitoring A total of 215 bird species breed in the UK on a regular basis (Gibbons et al. 1993). Over 80 % of those species are censused or surveyed on an annual basis through a variety of surveys supported by government and non-government conservation organisations (Fig. 1: Greenwood et al. 1995). Specific surveys cover population changes of the Heron, wetland birds (10 species), seabirds (22 species), and rare breeding birds (56 species: being defined as having populations of fewer than 300 pairs). We envisage that a small number of birds (27 species) can be covered by improved collation of data collected by bird clubs, reserve wardens and raptor monitoring groups (Fig. 1). There is a group of ten species for which there is no specific survey at present. Figure 1. Monitoring of terrestrial breeding birds in the United Kingdom. The graph shows the approximate number of species monitored by various annual surveys and recording groups. The proposed monitoring of species covered by raptor and owls monitoring, and improved data collation, have yet to be implemented. Data from autumn Wetland Bird Survey counts would be used to monitor a small number of breeding waterfowl which are not covered by other schemes. The remaining breeding birds (89 species) represent the common and widerspread species of the countryside and these form the focus of BTO's annual monitoring programme. At this scale, it is not feasible nor efficient to count or estimate total population sizes as it is for the rarer species, and monitoring must be based on sample surveys. For the information to be of greatest use, it is crucial for the sample of sites to be representative of the countryside as a whole. The primary objective of bird monitoring, or more strictly surveillance, is to provide an index of population changes from year to year. Although the terms monitoring and surveillance tend to be interchanged in the literature, monitoring implies (1) the measurement of changes against predefined standards of targets, (2) the collection of supplementary data to help intepret and understand population changes, and (3) that there are clear objectives (Baillie 1990, Furness & Greenwood 1993). - 102 -
COMMON BIRD CENSUS The Common Bird Census (CBC) has been the main monitoring tool for common birds in the UK over the last 30 years. The CBC is based on territory mapping and is one of the longest running schemes of its kind in Europe, having been established in the early 1960s (Marchant et al. 1990). It has proved highly valuable in advancing our knowledge and understanding of population fluctuations among British birds (e.g. O'Connor & Shrubb 1986, Marchant et al. 1990, Baillie 1990, Greenwood & Baillie 1991, Peach et al. 1991, Fuller et al. 1995, Greenwood et al. 1995). There is general consensus that territory mapping provides a reasonable estimate of most territorial populations (Dawson 1981, Verner 1985, Verner & Ritter 1988, Bibby et al. 1992) and the aims and methods of the CBC have been reviewed on a periodic basis (O'Connor & Fuller 1984, Marchant et al. 1990, Baillie & Marchant 1992). Despite the considerable achievement of the CBC, the scheme has a number of limitations and the BTO has been exploring alternative methods for population monitoring for some time (Baillie & Marchant 1992, Gregory et al. 1994). The limitations of the CBC are as follows: 1. Survey sites are not chosen at random. In consequence, there is the potential for species, geographical and habitat bias. In fact, the CBC has been restricted to farmland and woodland, and other habitats have been excluded. The distribution of survey plots mirrors the distribution of the human population and is baised towards the south and east of the UK. 2. Fieldwork, data compilation and mapping analysis are extremely time consuming (Gregory et al. 1994). Fieldwork involves nine or ten visits to a census plot each breeding season and many hours in data collation. Note that in Britain territory analysis is carried out by BTO staff rather than by volunteers, as is the case in other countries (van Dijk 1992). The time required for territory mapping fieldwork and analysis is roughly seven times that of an equivalent technique, such as point counts (Gregory et al. 1994). Taken together, these factors have limited the expansion of CBC coverage in the UK and to some extent limited the use of the data, although much can be done at the analytical stage to alleviate problems (Greenwood et al. 1995). Over a number of years the BTO has tested a number of new approaches to population monitoring in a UK setting (Gregory & Baillie 2004). The aim is to develop a monitoring scheme based on a formal sampling strategy for volunteer birdwatchers which uses simple and efficient methods and thus allows large numbers of people to participate over a wide geographical area. ALTERNATIVES TO TERRITORY MAPPING Line and point-count transects The obvious alternatives to territory mapping are line or point count transects, both of which are relatively efficient and have been used widely in population monitoring in Europe and North America (Bibby et al. 1992). A number of field trials have tested the suitability of these methods (Gregory et al. 1994, Gregory & Baillie 2004). They showed the comparability of monitoring results derived from different counting methods, the efficiency of the methods, and the practicability of using randomly chosen survey sites in the UK. A line transect approach was recommended because it was preferred by volunteers and was slightly more precise. Furthermore, line transects can be applied effetively in a wider range of habitats than point counts (Bibby et al. 1992). - 103 -
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