Náttúrufræðingurinn - 1954, Page 43

ISLENZKIR FUGLAR X
183
Molluscs with hard shells are cracked open by dropping them from the air, and
the same method is applied to hardshelled birds’ eggs such as goose eggs. The great
blackback is also a great scavanger feeding upon all kinds of carcasses, wastes from
the fisheries and slaughterhouses, and refuse from dumps and sewers. On the dumps
of Reykjavik many thousands of great blackbacks gather during the winter and
remain there until March when the huge shoals of capelin move to the inshore
waters of SW. Iceland for spawning. Then the great blackbacks leave the dumps
and tum to the capelin. Similar concentrations of great blackbacks occur on the
dumps and at the sewers in other towns and villages as well as in fishing centres
where great quantities of fish-offal accumulate.
There is no doubt that there has been a very pronounced increase of the great
blackback in Iceland in tlie last decades. Owing to lack of observations, however,
we cannot tell with certainty when this increase started, and for the same reason
it is not possible to cite any statistics regarding this increase. I believe that the
cause of this increase is first and foremost to be ascribed to greatly improved eco-
logical conditions for the great blackback in Iceland as a result of the rapid develop-
ment of the fisheries in Icelandic waters as well as the recent growth of towns, vil-
lages and fishing centres. Considering what has been said about the food of the
great blackback it is evident that all these changes must have been decisive in pro-
viding the great blackback with a rich food supply throughout the year. In former
tjrries the winter lias very probably been the critical period for the great blackback
in this respect, and this might well have been a chief factor in limiting the popula-
lion. In addition to the problem of food, it is, however, also possible that the milder
winter climate in the last decades may also have contributed to this increase. It is
not unlikely that the great blackback as well as other sea-birds suffered from the
severe winters of foriner times, especially when large parts of the coast were block-
ed by pack-ice.
Leiðrétting.
I síðasta hefti Náttúrufræðingsins urðu þau mistök, að burtu féll siðasta orðið
í grein Steindórs Steindórssonar: „Flóra Grímseyjar". Setningin (s. 143) er rétt
þannig: „Vart venður greinilegs skyldleika i þessu efni við þær eyjar aðrar, sem
flórulistar eru kunnir úr, í kalda sjónum við ísland.“