Abstract from BTO Research Report No 281:

Leech, D.I., Rehfisch, M.M. & Atkinson, P.W.

A guide to waterbird alerts
ISBN: 1-904870-68-6 31pp

Executive summary

1. The Alerts System provides a standardised technique with which to monitor changes in the population sizes of wintering waterbirds in the UK over a range of spatial scales and time periods using data collected as part of the Wetland Bird Survey (WeBS)

2. The total numbers of 37 species of wader and wildfowl observed during synchronised monthly counts are recorded at approximately 2000 wetland sites in the UK. Using these data, annual indices are calculated for each species.

3. During the Alerts process, the influence of short-term fluctuations and sampling errors on annual population indices is reduced using a smoothing process (Generalised Additive Model). This reduces the probability of categorising populations as declining in the long-term when observed decreases are in fact temporary, caused by factors such as harsh winters or disturbance.

4. Proportional population changes over a series of time periods (5-, 10- and 25-year and full data set periods) are calculated from the smoothed indices at a range of spatial scales. Population declines of between 25% and 50% are flagged as Medium Alerts and changes of greater than 50% as High Alerts. Equivalent increases in population size can also be flagged.

5. Alerts are intended as advisory measures triggering further investigation and should be interpreted with reference to the population dynamics and abundance of the species involved.

6. Population monitoring at the level of the individual site is vital if the “Favourable Conservation Status” of individual Special Protection Areas (SPAs) is to be maintained. Alerts at individual sites should be interpreted in light of population trends at larger spatial scales. Of particular concern are those SPAs where species are declining at a rate of greater than 25% over a specified time period when the larger-scale regional or national trends indicate stable or increasing population sizes.

7. All sites falling into this category will be short-listed for Level 1 Interpretation, which involves rapid assessment of all factors with the potential to negatively influence waterbird population sizes, with the exception of those pertaining to operations and permissions. If the factors responsible remain unidentified, sites will be retained for Level 2 Interpretation, which involves systematic investigation of site-based issues via analyses of existing data sets and discussions with local experts. Finally, if the reason for the observed decline is still not apparent, population trends will be examined in relation to Environment Agency water quality data.

Back to Research Reports 248-286