V 14 No.4 - The Scottish Ornithologists' Club

214 Short Notes 58 14 (4)
Red-breasted Mergansers moulting in Galloway
There are, apparently, few localities on the
west coast of Scotland where moulting Redbreasted
Mergansers Mergus serrator occur.
A flock of international importance (more
than 400) has been recorded in the Sound
of Gigha and flocks of more than 40 in
Wester Ross and the Ayr coast (Thorn,
1986). Other moulting areas occur at Loch
Linnhe (Prater, 1981) and at Mull (Scottish
Bird Reports).
Nationally important numbers (more
than 75) also occur at Luce Bay and Loch
Ryan, Galloway, with some peak counts just
below the numbers of international importance.
Table I gives the peak counts of
there in August and only 40 at Loch Ryan.
A similar pattern occurred in 1986 (not included
in the table) when 330 were moulting
in Luce Bay and only 20 in Loch Ryan.
Numbers have fluctuated from year to
year probably depending on the number of
males, non-breeders and juveniles present.
In Galloway they begin to build up at these
two estuaries from July and reach peak
numbers usually up to September. According
to Cramp and Simmons (1977),
however, females sometimes moult for a
month longer than males and this may account
for the numbers which occur up to
late September here. They usually begin to
TABLE 1 Peak counts of moulting Red-breasted Mergansers at Luce Bay and Loch Ryan, Galloway,
1966-1985 (in 5 yearly intervals).
Years
Luce Bay
Av. Range
1966-1970 38 26-62
1971-1975 19 ~1
1976-1980 2 0-12
1981-1985 98 190-300
Loch Ryan
Combined Total
Av. Ran~e Av. Range
90 16-200 128 56-224
187 73-294 206 78-355
232 130-350 234 130-350
186 40-290 284 152480
moulting mergansers occurring at Luce
Bay and Loch Ryan in August/September
between 1966 and 1985. The highest combined
counts were 355 in 1973,350 in 1980,
480 in 1982 and 340 in 1983, the 1982 count
being above the level of international
importance.
Loch Ryan is apparently more
favoured than Luce Bay and in six years out
of twenty no moulting birds were found at
Luce Bay. In only one year, 1983, was Luce
Bay the more favoured, with 300 counted
decrease in October I November but some
probably remain, at times in sizeable flocks
(up to 200), through to December.
References
Cramp, S. & Simmons, K.E.L. eds. 1977. The
Birds of the Western Palearctic. Vol. I.
Oxford Univ. Press, Oxford.
Prater, A.I . 1981. Estuary Birds of Britain and
Ireland. T. & A .D. Poyser, Calton.
Thorn, V.M . 1986. Birds in Scotland. T. & A.D.
Poyser, Calton.
R. C. Dickson, Seabhag, Stoneykirk, Stranraer DG9 9DH.