Report 434
Aerial surveys of aggregations of seaducks, divers and grebes in UK inshore areas outside the breeding season in 2007/08
(2009)
Lewis, M., Wilson, L.J., Sohle, I., Dean, B.J., Webb, A & Reid, J.B
From December 2007 to March 2008, the Joint Nature Conservation Committee
(JNCC) conducted aerial surveys of non-breeding aggregations of seaducks, divers and grebes within a number of Scottish inshore areas. The aim of the surveys was to collect data on the numbers and distribution of inshore waterbirds in areas of the UK known to be important for these groups of species. The surveys were carried out as part of the JNCC annual programme of surveillance of non-breeding populations of inshore waterbirds in the UK.
The areas surveyed by aircraft were: Luce Bay; the Firth of Clyde; the Sound of
Gigha; Loch Indaal (Islay); Coll and Tiree; Wester Ross Inner Sound and sealochs;
north Orkney; and east Unst, east Mainland and south-west Mainland areas of Shetland. Surveys were conducted from light aircraft, following a line-transect method designed to collect data that are suitable for both distance sampling (to estimate total numbers of birds by correcting for a decrease in detectability with increased distance from the transect line) and spatial modelling (to identify areas with the highest densities of birds).
Summary
Aerial surveys are only a component of
the winter survey programme because in some cases, aerial survey
methods may miss some species, e.g. species that avoid aircraft, or
species that are close inshore and are missed by observers while
the aircraft is banking at the coastline. Shore-based counts can
potentially collect data on some species that might be missed by
aerial surveys, although the offshore extent of such counts can be
limited. Boat-based surveys can potentially collect data on some
species that might be missed by aerial surveys, while retaining the
ability to survey the offshore extent of aggregations. In addition
to aerial surveys, the JNCC winter survey programme included
shore-based counts of inshore waterbirds within the upper Firth of
Clyde, selected areas of the Outer Hebrides, and the inshore waters
north of Orkney Mainland. These counts collected additional data on
the numbers and distribution of inshore waterbirds and attempted to
count the total numbers of birds present within the survey areas.
Several boat surveys were also conducted around Shetland by an
external contractor to collect additional data on the numbers and
distribution of great northern divers and Slavonian grebes in the
area.
Only the aerial surveys conducted by
JNCC in Scottish waters are considered in this report. This report
outlines the methods used during the 2007/08 winter aerial surveys
and presents the recorded numbers and distributions of the species
observed in each survey area.
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ISSN 0963 8091
Please cite as: Lewis, M., Wilson, L.J., Sohle, I., Dean, B.J., Webb, A & Reid, J.B, (2009), Aerial surveys of aggregations of seaducks, divers and grebes in UK inshore areas outside the breeding season in 2007/08, JNCC Report 434, ISSN 0963 8091