Abstract from BTO Research Report No 443:

Banks, A.N., Ellis, P., Holloway, S.J., Holt, C., Horner, R., Maclean, I.M.D., Marchant, J., Musgrove, A.J., Schofield, R.A., Sheldon J. & Stenning, J.

Surveying waterbirds in Morecambe Bay for the Wetland Bird Survey (WeBS) Low Tide Count Scheme.
ISBN: 1-904870-76-7

Executive summary

1. Morecambe Bay, north west England, is situated at the confluence of four major rivers (Kent, Leven, Lune and Wyre) and holds the largest continuous area of intertidal habitat in the UK. It is designated as a Special Protection Area (SPA) and Ramsar site on the basis of its non-breeding waterbird interest.

2. The Wetland Bird Survey (WeBS) is divided into two schemes: Core Counts, which aim to quantify bird numbers when aggregated at roost sites, and Low Tide Counts (LTCs), which aim to elucidate distribution of waterbirds across likely feeding areas.

3. Large sites such as Morecambe Bay are often difficult to survey at low water, owing to problems such as the range of visibility, access to potentially dangerous areas of intertidal habitat, and attracting numbers of volunteers necessary to achieve full coverage.

4. A first attempt was made to undertake co-ordinated counts of the four Sites of Special Scientific Interest (SSSIs) within the bay, including five main estuarine channels covered using standard methodology. The remainder of the bay was covered by aerial survey. Four counts were made in total, one during each winter month (November – February).

5. Bird distribution data were plotted on pre-defined sectors on the estuarine areas, and assigned to cells of a 1 km2 grid for the aerial survey counts. Relative density of birds at low water across the whole of Morecambe Bay could thus be determined for the winter. Important areas for each species found in nationally or internationally important numbers at the site are considered.

6. Cluster analysis revealed significant ‘hot spots’ of Oystercatcher and small waders within the bay. Although mean distributions of these species sometimes overlapped with high densities of cockles and Macoma bivalves, no relationship was found between mean bird densities and mean bivalve densities.

7. Disturbance events appeared to occur where recorded bird density was comparatively low, but there are likely to be issues with the resolution of bird data.

8. No obvious patterns in temporal use of different parts of the bay were evident, with mean centres of both Oystercatcher and small waders tending typically towards the east and middle of the bay.

9. Estimates of counter error were made from aerial survey simulations, with an estimated overall mean error of –31%. At this level of error, corrected aerial survey counts would still represent underestimates of Core Count figures from 2004/05.

10. Further ground-truthing of aerial survey counts was not possible to any degree of accuracy, but broad comparison of counts of one area made by standard and aerial survey suggested again that aerial surveys returned lower counts.

11. The suitability of aerial survey for use in WeBS LTCs at Morecambe Bay and at other large sites is discussed. Refinements to standard ground survey practice at Morecambe Bay are also suggested.

12. Further research necessary to more closely determine feeding behaviour and distribution of waterbirds within Morecambe Bay is considered.

13. Preliminary analysis of digital images of intertidal habitat taken at another large site with internationally important numbers of waterbirds (The Wash), obtained through collaboration with RAFOS, is outlined, as are recommendations for the advancement of this approach.

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