Náttúrufræðingurinn - 1975, Blaðsíða 52

42
NÁTTÚRUFRÆÐINGURINN
S U M M A R Y
Arctic terns (Sterria paradisae) robbing fish off black guillemots (Cepphus
grylle) in Northwest lceland
by
Hjálmar R. Bárdarson,
P. O. Box 998, Reykjavík.
Observations on the interactions of artic terns (Sterna paradisaea) and black
guillemots (Ceppus grylle) in July 1973 at the island Aedey, ísafjardardjúp,
N.W. Iceland, are reported.
The guillemots caught small fish off the island which they brought back on
the wing, often landing on a small closed in bay near the breeding grounds.
They then generally swam ashore and, still carrying one fish in their beaks,
scuttled into a nest crevice. After a short wltile, having fed the young, they
would reappear and after a short rest set out on another trip. Arctic terns
often harassed guillemots when they had brought fish ashore. The guillemots
triecl to avoid the terns, sometimes by scurrying into a nest crevice, sometimes
by fleeing out to the bay and diving for prolonged periods. A tern would
then follow and attack the guillemot whenever it surfaced. After a while the
guillemots tired and released the fish on the surface. The fish was then picked
up by the tern which would then take it to its young. After a while the
guillemot would fly off on yet another fishing trip. Guillemots not carrying
fish were never harassed by terns. Although it was well known to the inhabi-
tants of Aedey that the arctic tern frequently pirate fish off the black guillemot,
this behavior apparently has not been previously reported in the literature.
However, arctic terns have been reported robbing horned grebes (Podiceps
auritus) in Iceland (Bengtson 1966), and robbing behavior of Sterna dougallii
(Dunn 1973) ancl Sterna hirundo (Hays 1970) has also been reported. Berg-
mann (1971) records successful pirating of black guillentots by Larus canus
and Winn (1950) recorded occasional ancl unsuccessful attempts of Larus
argentatus at robbing black guillemots.