Náttúrufræðingurinn

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Náttúrufræðingurinn - 1979, Qupperneq 95

Náttúrufræðingurinn - 1979, Qupperneq 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
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