Náttúrufræðingurinn - 1997, Blaðsíða 12

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■ SUMMARY
ROCK PTARMIGAN STUDIES AT
KVÍSKER, SOUTHEAST ICELAND
1963 TO 1995
The Icelandic Rock Ptarmigan (Lagopus
mutus) population fluctuates in size and ca. 10
years have been between peak years (Finnur
Guðmundsson 1960, Amþór Garðarsson 1988,
Ólafur K. Nielsen and Gunnlaugur Pétursson
1995). To monitor population changes territo-
rial cocks (Fig. 1) are counted each spring on
selected plots in different parts of the country.
The purpose of this paper is to report the re-
sults of ptarmigan censuses and banding at
Kvísker (63°59’N, 16°26’W) in SE-Iceland
(Fig. 2). The total area of the ptarmigan study
plot is 2.1 km2, and it is located on a south fac-
ing slope on the foothills of the great glacier
Vatnajökull. The farm Kvísker is within the
study plot. The lower edge of the plot is at 30 m
above sea level and the upper edge is at 120 m.
The characteristic vegetation is birch scmb
(Betula pubescens) and open areas with
heathland vegetation such as Empetrum nigr-
um, Vaccinium uliginosum and Racomitrium
lanuginosum. Territorial cocks were censused
once each year in the period 12 to 20 May. The
census was timed so as to be over before folia-
tion of the birch scmbs, and was always com-
pleted in one day. In some years more than one
spring census was conducted and the count giv-
ing the highest figures was used. Ptarmigan
were caught for banding at Kvísker by driving
them into corrals or by snaring them, using
stuffed birds as decoys (for cocks in spring)
(Ólafur K. Nielsen 1995a). All censuses and
banding has been done by the same person
(Hálfdán Bjömsson), who also made all but
seven of the recoveries and all of the controls.
In the period 1963 to 1995 the average
number of territorial cocks was 20.5 (9.8
cocks/km2). The maximum fígure was 53 cocks
(25 cocks/km2) and the minimum 7 cocks (3.3
cocks/km2). The difference in numbers be-
tween the highest and the lowest year was ap-
proximately 8-fold. Population trends are
shown in Fig. 3. There was a clear peak in
numbers in 1966. Following low years in 1970
and 1971 the population increased to medium
density levels in the early 1970s and remained
at such levels for 10 years. This was followed
by a decrease starting in the mid 1980s and
reaching a low in 1991 and 1992 and then
again an increase.
Compared with 7 ptarmigan census plots in
N- and NE-Iceland the Kvísker plot ranks
among the denser ones, being surpassed only
by Hóll on Tjömes (Ólafur K. Nielsen 1995b)
and Hrísey (Ævar Petersen 1991). On Hrísey
density was 41 cocks/km2 during a peak year
(Ævar Petersen 1991). Comparing population
trends for Kvísker, Hrísey and six plots in NE-
Iceland we found that all areas behave more or
less in the same fashion with regard to changes
in numbers (Fig. 4).
A total of 916 ptarmigan had been banded at
Kvísker at the end of the year 1995. This in-
cluded mostly young of the year (juve-
niles,753), but also adult hens (91), cocks (64)
and unsexed full-grown birds (8). Fifty-one
ptarmigan (6%) have been recovered dead. The
most common cause of death was collisions
with barbed wire fences or overhead wires
(Fig. 5). The recoveries give a biased picture of
death causes, as birds killed by predators are
underestimated and importance of collisions
and hunting is overestimated.
Sixty controls of ringed ptarmigan have been
made and all at Kvísker. Thirty-four adults of
155 banded (21%) were recovered or control-
led at Kvísker but only 70 (9%) of 753 juve-
niles. This difference between age groups is
significant (chi-square=14.137, p«0.001),
and probably reflects both juvenile dispersal
and higher mortality of juveniles during fírst
winter as compared with adults. Juveniles are
banded in late summer and most recoveries and
controls are made the following spring and
summer but few during the preceding winter
when most of the mortality takes place.
Thirty-four ptarmigan banded as juveniles
122