Náttúrufræðingurinn - 2023, Blaðsíða 77

8. mynd. Djáknatjörn í Krossanesborgum tekin úr lofti með dróna til norðurs. – Tarn Djáknatjörn in Krossanesborgir nature reserve.
Ljósm./Photo: Eyþór Ingi Jónsson, 18.05.2018.
Samkvæmt niðurstöðum merkinga
fara íslenskir hettumáfar mest til Evrópu
á veturna, auk þess sem margir verða
eftir á Íslandi og einstaka fara vestur
um haf.1, 16 Talsverður hluti þeirra hettu-
máfa sem hafa verið merktir á Íslandi
og endurheimst á Bretlandseyjum voru
merktir á talningarsvæðinu í Eyjafirði,
við Skipalón í Hörgársveit.17 Orsaka
breytinga á íslenska varpstofninum
gæti því frekar verið að leita á vetrar-
stöðvunum en á varptíma á Íslandi.
SUMMARY
Black-headed Gulls in Eyjafjörður
(N-Iceland) 2020
Since 1990 Black-headed Gulls (Chro-
icocephalus ridibundus) (Fig. 1) have
been monitored every fifth year in the
fjord of Eyjafjörður, N-Iceland. The
monitoring area is 556 km², and all be-
low 200 m a.s.l. (Fig. 2). This is the only
large area in Iceland where distribution
and numbers of this species are moni-
tored. Black-headed Gulls are censused
using the following methods (depend-
ing on local circumstances): (1) nests
with eggs or young, (2) empty nests, (3)
number of incubating birds, and (4) to-
tal number of birds at nesting site.
The Icelandic breeding population
of Black-headed Gulls was estimated
25.000-30.000 pairs in 350-400 colo-
nies, but this estimate has not been re-
vised since 1998. In 2020 the number of
pairs in the Eyjafjörður monitoring area
was 1922. This time Black-headed Gulls
nested at 23 sites (Fig. 5). Two of these
sites are shown (Figs 7 & 8), another
one was submerged due to meltwater
during first census attempt (Fig. 3), one
was censused using a drone, since the
birds nested in tall sedge and the nest-
ing birds could not be counted from dis-
tance (Fig. 4).
Since 1990 Black-headed Gulls have
been found nesting at 89 sites (included
in article on webpage natturufraedin-
gurinn.is). Between 1990 to 2005 the
population declined steadily but has in-
creased continually since then. In 2020
the population was larger than ever
before since monitoring begun in 1990
(Fig. 6). The total increase was 26%
from 2015 to 2020.
Interestingly identical changes have
taken place in the breeding population
of the Black-headed Gull in Eyjafjörður
and in the UK. This could indicate
that the same factors are responsible
for changes in these two populations.
Black-headed Gulls have only nested
in Iceland for over a century, first nest
found in 1910. Most of the Icelandic
birds overwinter in Europe, many in
the UK, where large numbers of birds,
ringed in the monitoring area, have
been recovered. Many Black-headed
Gulls overwinter in Iceland, and some
have been recovered in N-America.
Ketill Þór Thorstensen, Snævarr Örn Georgsson
og Sunna Björk Ragnarsdóttir tók þátt í talningum.
Anette Theresia Meier gerði kortin. Gísli Kristins-
son lánaði eina mynd. Þau fá öll bestu þakkir.
ÞAKKIR
165
Ritrýnd grein / Peer reviewed