The areas surveyed in both winters were the Moray and Inverness Firths, the Firth of Tay and the Firth of Forth. The Beauly Firth was included in surveys of the Moray Firth area in 2000/01 while the Dornoch Firth was included in 2001/02. In addition, one-off surveys were made of; Loch Indaal (Islay); the Solway Firth; part of the Angus coast; and Cardigan Bay in 2000/01; and the Thames Estuary and Suffolk coast in 2001/02.

The survey methods used differed between the two winters. The 2000/01 surveys were conducted using a strip-transect method in which observers attempted to make a total, direct count of birds in each survey area. The 2001/02 surveys were conducted following a line-transect sampling method, designed to allow the use of statistical analyses (distance sampling) to estimate the number of birds missed by observers and therefore produce estimates of total bird numbers in each survey area.

 

Eleven species of seaduck, divers and grebes were identified and recorded during these surveys. In addition, some birds could not be identified to species level and were therefore recorded only as diver species, grebe species, scoter species or seaduck species.

 

Red-throated divers were by far the most numerous diver recorded during these surveys and were recorded in all areas except Loch Indaal, with the largest numbers recorded in the Moray Firth, Cardigan Bay and the Thames. Only small numbers of great northern divers were recorded in the sealochs of North East Scotland and Loch Indaal, while a single black-throated diver was counted in the Moray Firth. In addition, large numbers of divers were recorded as unidentified diver species in many of the survey areas.

 

Great crested grebes were the only grebes recorded to species level. These were most numerous in the Solway Firth, although small numbers were also recorded in Cardigan Bay, the Thames Estuary and the Moray Firth.

 

Of the seaduck recorded, black scoter and common eider were the most numerous with similar total numbers recorded overall. Smaller numbers of (in descending count order) long-tailed duck, velvet scoter, greater scaup, red-breasted merganser and common goldeneye were also recorded.

 

Greater scaup were recorded in greatest numbers in the Solway Firth and Loch Indaal. Common eider were recorded in highest numbers in the Firth of Forth and the Firth of Tay/St Andrews Bay, while the greatest numbers of long-tailed duck were recorded in the Moray Firth. Black scoter were recorded in all areas surveyed, with the largest numbers recorded in Cardigan Bay. Velvet scoter were recorded in highest numbers in the Firth of Forth. In addition, significant numbers of unidentified scoter species were recorded in the Firths of Moray, Tay and Forth. Red-breasted mergansers were recorded in greatest numbers in the Beauly and Inverness Firths, the Firth of Forth and Cardigan Bay.

 

This report describes the methods used during aerial surveys of seaduck, divers and grebes during the winters of 2000/01 and 2001/02, and presents the numbers and distributions of those species recorded in each area. However, differences in survey coverage and methods between years, plus the lack of a comparable long-term dataset, preclude conclusions on trends in numbers or distribution. We also discuss the limitations of the methods and data presented here and suggest potential developments and improvements for future aerial surveys.