Population Sizes of Seabirds breeding in Scottish Special Protection Areas

2 Methods

Data were obtained from the JNCC's Seabird Monitoring Programme ( SMP), as well as requesting any data that was not submitted to the SMP from SNH , bird observatories such as Fair Isle and Isle of May, or any other regularly manned and monitored reserves, such as Handa Island SWT , or Marwick Head RSPB. These data were then collated together into a single Excel spreadsheet, where they could be arranged in order of SPA, species, and year. If there were multiple counts for the same count site in the same year, these were considered to be partial counts and were summed.

There were several issues identified with collating the data available. The SMP began before the Birds Directive and the need for SPA designation, and consequently the count areas and sites used are not necessarily compatible with the boundaries of relevant SPAs. A simple GIS based approach to isolating the relevant count sites within the SPAs and an additional 100 m buffer was intended originally, but was rejected due to the following difficulties:

• Positions for count sites frequently refer to start or end points of linear count sections. The end of an SMP count section might fall within an SPA, but the majority of that section may lie outwith the SPA boundary. Likewise, a section might be excluded from the dataset due to an end point falling just outside an SPA boundary.
• Some SMP positions refer to central points of km ² count areas. In these instances, an SPA boundary may cut through part of the count area.
• Some SPAs encompass areas that are smaller than individual SMP count sites. For example, a portion of western Stroma is included within the North Caithness Cliffs SPA, but the SMP count site for Stroma encompasses the whole island, thus including this site could include birds from outside of the SPA.
• The SPA shapefiles are extremely accurate. Inaccurate recording of SMP count 'site' positions could lead to their exclusion from relevant SPA datasets.
• Different (and incompatible) count methods were sometimes used at count sites. For example, a count of a colony of terns may be of 'apparently occupied sites' one year, and 'individuals on the ground' in another.
• The buffer zone could contain data on species from outside the SPA.

Therefore, the majority of count sites were selected manually, by eye, by the JNCC's SMP coordinator. For a small number of SPA's this was deemed an unsuitable approach (Fetlar SPA, Hoy SPA, Papa Stour SPA, Papa Westray SPA, Rousay SPA, and South Uist Machair and Lochs SPA). It was therefore decided in conjunction with JNCC (Roddy Mavor) to apply a GIS based approach to isolate count sites within these SPAs, using a spatial join tool. The spatial join tool overlays the count sites with the SPA shapefiles, thus isolating all positions that fall within the boundaries of an SPA.

Where necessary some incompatible counts (due to count type) were eliminated. The data presented here represents the largest dataset of compatible counts for each species at each SPA. Most of the variation in count types pertains to different ways of counting or expressing breeding 'units'. Therefore, the following count types were selected as being compatible with each other, and referring to breeding 'units', and are referred to in the tables as 'pairs':

• Occupied nests;
• Occupied sites;
• Occupied burrows;
• Occupied territories.

Counts for auks were predominantly of individuals on land apart from Atlantic Puffins, which were counted in occupied burrows. (Counts for individuals on land have been used as a proxy for occupied burrows in some innaccessable sites, meaning that some SPAs include data of both types. This is clarified in the text). Once the data from all sources had been collated, the inconsistencies within the dataset necessitated the setting of some parameters for data representation. Here, each SPA is broken down into its interest features ( i.e. the species it is designated to protect), with a data summary for each of these features.

• All of the available data for each SPA feature is presented in a table, detailing counts, the years the counts were made, and the count type ( i.e. 'pairs' or individuals on land).
• Each feature of each SPA also has a table representing the requested statistics, based upon the data. This table includes:
  • SPA count site and name
  • N year mean - a mean of the latest 5 years data (or as many years data are available). The means are presented with the standard deviation (stdev, the average distance of points from the mean), the percentage coefficient of variation (%CV, the standard deviation expressed as a percentage of the mean, allowing assessment of the relative magnitude of the standard deviation), N (the number of yearly counts on which the summary statistics are based), and the year span (the possible number of counts between the first and last years on which the summary statistics are based).
  • A mean for and since Seabird 2000 (the last national census). Summary statistics are as above.
  • The most recent count, with the year.
• If whole colony counts are available, these are presented below count site statistics and called 'whole colony'.
• If all count sites are represented during some years, a row called total (sum of counts) is provided, with statistics (as above) for the total counts for those years.

Figures representing trends in the data since the last national census are presented where the data meet the following criteria. All compatable data available for each species at each count site is presented in the figures.

• More than four counts are available after and including the Seabird 2000 count (or after 2000, if there was no Seabird 2000 count).
• Five year moving average smooths, and polynomial smooths were applied to the data where there were seven or more data points.