As a partner in the Wetland Bird Survey we husband data from what is probably the longest running, most complete waterbird monitoring scheme in the world. This puts us in an enviable position and enables the unit to develop new methods that help gain scientific understanding of waterbird population dynamics, and improve the monitoring and reporting of population trends.

Indexing waterbird numbers

The widely used Underhill Indexing method was originally developed in collaboration with Prof. Les Underhill from the University of Cape Town. This indexing method forms the basis for all routine reporting of waterbird numbers in the UK and elsewhere including The Republic of Ireland and The Netherlands (Underhill & Prys-Jones1994).

Future developments will seek to incorporate habitat stratification to WeBS indices. Habitat stratification is important, as it will ensure that the indices are weighted by the relative frequency of occurrence of the habitats in the UK, rather than the present situation where a very completely counted habitat can contribute more to the index than a much more common but less completely counted habitat. This can lead to unrepresentative country-wide species trends for those species that inhabit a broad spectrum of habitats. We are currently compiling an inventory of water bodies throughout the UK. Once completed this will enable us to better understand how WeBS survey coverage relates to available habitat across the wider countryside and stratify our index computations accordingly.

Waterbird Alerts System

In collaboration with our counterparts from SOVON based in the Netherlands and Prof. Les Underhill from the University of Cape Town we have developed the WeBS Alerts system used to report back on alarming national and local (typically at the site level) waterbird trends to the UK Government (Atkinson et al. 2006, Austin et al. 2007). Smoothed trends, based on Generalized Additive Models, are used to reveal long-term trends underlying the population indices. Alerts are triggered when the numbers of a species declines by at least 25% (medium-alerts) or at least 50% (high-alert) over short-, medium- and long-term timeframes (5, 10 and 25 years). At the site level, in order to determine whether a decline is specific to the site (as if caused by habitat loss for example) or is occurring more widely (as if caused by climate change for example), comparisons are made to regional and national trends.

The purpose of these alerts is to focus attention towards the population trends that may give cause for concern to conservationists; such alerts are intended to precipitate focused investigation and subsequent conservation action where appropriate. (Click here to view the WeBS alerts online report)

This resource is establishing itself as the first port of call for those with an interest in waterbird trends, with over 80 SPAs and 50 SSSIs considered in detail. The alerts help meet the UK Government’s legal obligation to monitor these sites designated as being of conservation importance and to trigger any action needed to ensure that they remain in favourable status.

The current WeBS Alerts system is species orientated. In the future we plan to develop Site Indicators as a complementary assessment of a site’s overall ‘state of health’.

Waterbird Indicators

In addition to feeding waterbird indices into broad indicators that incorporate species from a variety of habitats (Wild Bird Indicators), we also produce national waterbird indicators for ‘The State of the UK’s Birds’.

Current methodological research is aimed towards developing indicators that will make use of stratified waterbird indices (see Indexing waterbird numbers), and we are developing and promoting the concept of a complementary, alternative indicator, in which the contributions from individual species are weighted according to their relative conservation importance in a wider geographical context. The latter aims to give a more outward looking indicator of waterbird trends than the introspective approach of traditional indicators - if the region / country of focus holds a relatively large proportion of a country / flyway population of a species then the species in question will have a relatively large influence on the overall indicator even if it is numerically much less common than an abundant but widely distributed species.

References

Atkinson P.W., Austin, G.E., Rehfisch, M.M., Baker, H., Cranswick, P., Kershaw, M., Robinson, J., Langston, R.H.W., Stroud, D.A., van Turnhout, C. & Maclean, I.M.D. 2006. Identifying declines in waterbirds: the effects of missing data, population variability and count period on the interpretation of long-term survey data. Biol. Conserv., 130, 549-559.

Austin, G.E., Maclean, I.M.D., Atkinson, P.W. & Rehfisch, M.M. 2007. The UK Waterbirds Alerts System. Waterbirds around the world. Eds. G.C. Boere, C.A. Galbraith & D.A. Stroud. The Stationery Office, Edinburgh, UK. Pp. 705-710.

Underhill, L.G. & Prys-Jones, R. 1994. Index numbers for waterbird populations. I. Review and methodology. J. Appl. Ecol., 31, 463-480.