Náttúrufræðingurinn - 1989, Side 29

land (e.g. Gudmundsson and Gardarsson
1986). These birds may include late arriv-
ing birds or failed breeders. Few Red-
shanks stayed on the flats in June. Num-
bers built up again in July and peaked in
late July; the last few birds were seen in
early November.
The Knot (Calidris canutus) was much
more abundant in Kópavogur than Graf-
arvogur (Fig. 9). The first migrants were
seen in Kópavogur on 14 April 1980 and 16
April 1981. In both years there was a tre-
mendous increase in the last days of April,
with peak numbers on 4 May 1980 (2310)
and 7 May 1981 (3100) followed by steep
declines. There was a second, lower, peak
10-12 days later in both years. The last
birds in spring 1980 were seen on 28 May.
This pattern of two peaks during the
spring passage of Knots in Kópavogur ap-
pears to be an annual event. In 1979 the
peaks were on 11 (2500) and 26 May (520),
in 1982 on 9 May (3100) and 21 May (630).
The two peaks coincided with spring tides.
Censuses in NW Iceland in 1979 (Gardars-
son et al. 1980) and SE Iceland in 1980
(Ingolfsson et ai. 1980) suggest that two
main waves of migrating Knots arrive in
Iceland. Birds staging in SW Iceland stay
for only a few days before passing on
north along the west coast. When the
Knots leave for the arctic in late May most
of the birds are well north of our study ar-
eas. The first adult Knots returned on 10
July, the first juveniles were seen on 29
July. Fewer birds were seen in late sum-
mer than in spring, the summer peak in
Kópavogur was only 31 birds. The main
food of four Knots collected in Grafarvog-
ur in May 1980 was Mya arenaria in three
and Cricotopus variabilis larvae in one,
other foods were Littorina spp. and Myti-
lus edulis. Of 11 Knots collected at the
nearby estuary Hvaleyrarlón 10 had eaten
mainly Mytilus edulis and one mainly Lit-
torina spp. (Table 3).
The Purple Sandpiper (Calidris mari-
tima) was only seen on the mudflats in late
winter and spring (Fig. 10). There is a
large local wintering popuiation on rocky
shores. In winter 1980-81 the first Purple
Sandpipers were seen on the mudflats in
January and February. Peak numbers oc-
curred in March and April. Most of the
birds had left by early May. Purple Sand-
pipers were absent from the estuaries in
summer through mid-winter. One Purple
Sandpiper collected in May 1980 in Graf-
arvogur had fed mainly on Cricotopus var-
iabilis larvae (Table 3).
The Dunlin (Calidris alpina) was abun-
dant (Fig. 11). The first migrants were
seen on 26 April 1980 and 24 April 1981.
They increased rapidly to a peak on 7-8
May 1980, and on 10 May 1981. There was
a second, smaller peak in Dunlin numbers
in late May 1980. Observations on an estu-
ary in SE Iceland in May 1980 revealed a
similar bimodal pattern in Dunlin num-
bers (Agnar Ingólfsson et al. 1980). Few
Dunlins were seen during most of June.
Numbers of adults increased again in late
June, reaching a peak on 8 July. These
birds passed through quickly and numbers
were considerably down when the first ju-
veniles arrived on 15 July. Most Dunlins
seen after mid-July were juveniles (Table
4). Their numbers remained more or less
constant until 11 August in Grafarvogur
and 3 September in Kópavogur when
there was a sharp decline. A few were
seen until 20 October. Five Dunlins col-
lected in Grafarvogur in May 1980 had ali
been feeding mainly on Cricotopus varia-
bilis larvae but had also taken small gas-
tropods and Mytilus edulis (Table 3). The
first spring peak in Dunlin numbers must
consist of Icelandic breeders that disperse
after a short stay on estuaries. The second
peak, in late May, may consist of arctic
Dunlins (subspecies arctica) enroute to
Greenland or Icelandic breeders returning
from the breeding grounds. Of three fe-
ntales collected at an estuary in SW Ice-
land in late May 1980, two had recently
completed laying.
Other shorebird species observed only
rarely were Snipe (Gallinago gallinago),
Whimbrel (Numenius phaeopus), Curlew
Sandpiper (Calidris ferruginea), Sander-
ling (C. alba) and Red-necked Phalarope
(Phalaropus lobatus).
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