The fulmar began nesting in the early 1920's on Runde, the only sizeable seabird colony in south Norway, off Alesund. Further immigration of birds from the British Isles probably occurred in the first 25 years, when the population increased about 10% annually to about 350 pairs in 1947 (Valeur 1947). Since then the population increase has slowed down to about 3% annually, and the population on Runde in 1971 was about 700 pairs (Table 9). From Runde, fulmars have spread not only to a number of islands in the same region, but also much farther afield—south to Utsira (59°18'N, 4°55'E) and north to Bleik (69°3'N, 15°42'E). The total Norwegian population of fulmars in 1971 was estimated at 1,100 pairs.
Fig. 4. Distribution of the razorbill (Alta torda) in Norway. Numbers refer to localities listed in Table 8.
Fig. 5. Distribution of the gannet (Sula bassana) in Norway. Numbers refer to localities listed in Table 10.
| Locality | Year | Sample size (number) | mx |
|---|---|---|---|
| Vedøy, Røst | 1972 | 852 | 0.21 |
| Hekkingen, Troms | 1974 | 264 | 0.46 |
| Hjelmsøy | 1974 | 357 | 0.18 |
| Jarfjord | 1974 | 146 | 0.31 |
| Total | 1,619 | 0.25 |
Gannet (Sula bassana)
The gannet (Fig. 5), the most recently established and least numerous of the cliff-breeding seabirds, has the best-known population change. Like the fulmar, it was established in 1946 on Runde, and the first individuals were undoubtedly of British origin. During its entire breeding history on Runde, and also in two of the three new colonies in northern Norway established in the 1960's, the yearly increase has far exceeded the intrinsic rate of increase (Table 10); for gannets with a 50% breeding success, adult mortality of 6%, and 35% survival up to first breeding, the intrinsic rate of increase is about 2% per year. The Runde and Syltefjord colonies are naturally protected by their inaccessibility, but the colonies at Mosken and Nordmjele, which are on small islets, are both easily accessible. The Nordmjele colony, however, has been effectively protected from its start, whereas the Mosken colony has been open to visitors; this difference is probably reflected in their different breeding success and annual growth rate (Table 11). The breeding success necessary to maintain a stable population with the mortality figures given above is 34%:
mx = (1-P)/1x = 0.66/0.35 = 0.17
For equal sex ratio, breeding success is 2 times mx = 0.34.