Náttúrufræðingurinn - 1980, Blaðsíða 178

above, Black Guillemots were very common
in 1908, and in the first three decades of the
present century. I believe rats had an
abundant food supply around the fish sheds.
In fact they were seldom seen on the eastern
part of the island, where the last few years
60—70% of all Black Guillemots have nest-
ed. The decline in the Black Guillemot
population occurred contemporaneously
with the eastward spread of rats on Flatey.
When the eradication of rats was started, the
numbers of Black Guillemots started in-
creasing. Although no figures are available
for 1971, I believe it no coincidence that the
greatest increase appears to have taken place
that year.
The rapid increase of Black Guillemots
since 1966 can only be explained by massive
immigration (A. Petersen, unpubl.). Since
an increase also appears to have happened
throughout the whole of Flatey civil parish, I
believe the birds must have come from out-
side that area, particularly from the main-
land counties to the north of Flatey (Barda-
strandarsýslur), where Mink have been ab-
undant since about the middle 1960’s. Mink
have not colonized Flatey civil parish, and
had not become firmly established in the
Bardastrandarsýslur by theendof the 1950’s
(Skaptason 1969). I hypothesize that young
Black Guillemots emigrated from their natal
areas as Mink became more common on the
mainland.
Puffins as possible nest competitors with
Black Guillemots
Noticeably few Puffins nest on Flatey (see
Table III), as is the case for many of the
inhabited islands of the parish. In contrast
Puffins are the most common and wide-
spread seabird species of the uninhabited
islands of Breidafjördur.
Where Puffins and Black Guillemots nest
in same island, their nesting areas are usu-
ally well separated (cf. Lack 1934). Puffins
often nest in boulder screes where Black
Guillemots appear to be able to nest. I be-
lieve Puffins successfully oust Black Guille-
mots when in competition for nest-sites.
In contrast to Puffins, Black Guillemots
normally nest in greatest numbers on the
inhabited islands. Size of the islands and the
abundance of acceptable nest-sites, are fac-
tors which have to be borne in mind in this
context, and the inhabited islands are nor-
mally among the largest. Yet Puffins are
noticeably warier than Black Guillemots. I
hypothesize that Black Guillemots would be
less common on Flatey if not inhabited, and
that human settlements have increased the
nesting possibilities for Black Guillemots.
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