Náttúrufræðingurinn - 1979, Blaðsíða 97

lings of this species occurred iu 1917
or 1918 (Hachisuka 1927, Pálsson
1936).
8. Barrow’s goldeneyes that leave the Mý-
vatn-Laxá mainly do so in late Octo-
ber and at least through November.
The main return movement takes
place in April, beginning in late
March. Adult males preceded females
and juveniles on the Sog, sw. Ice-
land, in the autumn. Females and ju-
veniles are niore migratory than adult
males; thus in Jan-Feb 1977 sex ratios
(total females/100 adult males) were 68
(n 1124) in the Mývatn region (in-
cluding the uppermost Laxá), 102 (n
451) on the lower Laxá and 104 (n 151)
in the Ölfusá watershed; the corre-
sponding ratios for juvenile males
were 5 (n 702), 57 (n 349) and 38
(n 102).
9. Up to 1976, 156 Barrow’s goldeneyes
(93 ad., 63 pull.) had been ringed in
Iceland. Thirteen adult females ringed
at Mývatn had been recovered, all
but 1 which was shot at Lón 50 knr
north were found dead at the ringing
locality. Several recaptures liad also
been made of fentales on their nests.
l’he recoveries indicate an annual
mortality rate of 0.3—0.4 which is
higher than suggested by census
estimates. In 1977 and 1978 94 (5 ad.,
89 pull.) were ringed, but there have
been no recoveries yet.
10. It is concluded that better estimates
are needed of (1) the number of fe-
males, (2) the number of breeders and
(3) the number of fledged young.
Further studies are required to show
conclusively whether censuses in Ice-
land account for the entire Icelandic
population or whether there is a
non-breeding segment in eastern
Nortli America. To establish these
points, censuses should be continued
and ringing increased greatly. A more
realistic population model may then
be constructed, perliaps followed up
by experimental manipulation of the
population to test hypotheses of how
it is regulated.
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