Náttúrufræðingurinn - 1979, Síða 95

Todd, W. É. C. 1963. Birds of the Labra-
dor Peninsula and adjacent areas.
Toronto.
S U M M A R Y
Distribution and numbers of the
Barrow’s goldeneye (Bucephala
islandica) in Iceland
hy Arnthor Gardarsson,
Instilute oj Biology, Universiiy of Iceland,
Grensásvegur 12, lleykjavik
1. Distribution and numbers ol Barrow’s
goldeneye (Bucephala islandica) in lce-
land were studied during 1975—78.
The work formed part of a continuing
study ol duck populations of the Mý-
vatn-Laxá watershed, n. lceland (Gard-
arsson 1979). Barrow’s goldeneyes are
conspicuous birds with a very limited
distribution in Iceland, hence numeri-
cal changes are relatively easily fol-
lowecl and it should be possible to
make direct field estimates of popula-
tion dynamics.
2. Aerial surveys from light aircraft co-
vered almost all suitable habitat in
May-June, July-August and in Janu-
ary-February. Intensive ground work
was carried out mainly in summer at
Mývatn-Laxá where almost the entire
population bred and nearly all males
moulted. Ground work in winter was
less intensive and was mainly limited
to the Mývatn-Laxá and the river Sog
and other lakes and rivers of the
Öllusá system in sw. Iceland.
During censuses each bird was sexed
and aged with the maximunt possible
accuracy. The two age categories used
here are juvenile (up to June o£ lst
yr of life) and aclult (including birds
presumed to be in their 2nd yr and
hence non-breedingj. In any one
census a small but variable proportion
could not be determined with the
desired accuracy. Since accuracy
largely depended on distance, all adult
inaies were usualiy determined, except
during eclipse, and accuracy was lo-
west when aging females. The totals
for eaclt category in each iocality were
adjusted to include undetermined
birds in the same proportions as in the
determined sample.
3. A brief review is given of the general
distribution of the species with emp-
hasis on the eastern part of the distri-
bution. This is summarized as lollows:
St. Lawrence — New England: regular
winter visitor with a major concentra-
tion in the St. Lawrence estuary (Recd
& Bourget 1977). Labrador: no evi-
dence of breeding, but information
apparently lacking for largc parts;
moults in some numbers along the
coasts of Ungava (Hantzsch 1908, Todd
1963). Greenland: several occurrences,
especially in winter (Salomonsen
1950); evidence for a single breeding
occurrence seems questionable. Thus,
the origin of Barrow’s goldeneyes in
Greenland and eastern North America
is problematic; the existence of an un-
known breeding population or an
unproven connection with the Iceland
breeding population is intplied.
4. Winter distribution in Iceland (Fig
4) is confined to spring-fecl fresh
waters in the young volcanic zone,
mainly in the Laxá watershed (86%
of the known wintering population
of 2023 in January 1977, cf. Table 1);
as well as the Sog and Brúará river
systems, s. Iceland (9%); the Veidi-
vötn in the s. highlands (3%); Medal-
land, se. Iceland (2%); and Lón, ne.
Iceland (1%).
The breeding range (Fig. 5) is centred
on Lake Mývatn and the uppermost
Laxá river which together account
for at least 95% of the breeding
population, some also breed scattered
over other parts of the Laxá system
and along the tributaries of tlie nearby
Skjálfandafljót. A few adult pairs and
non-breeders are also found in summer
in all known wintering areas except
the Veidivötn (wltere information is
189