[72] The "number of pairs" is calculated by multiplying the number of birds observed by 0.67 (Dyck and Meltofte 1975).
[73] A few species breed near freshwater lakes, but are marine during the nonbreeding season.
[Present Status and Trends in Population of Seabirds in Norway]
by
Einar Brun[74]
University of Tromsø
Tromsø, Norway
Abstract
The most numerous seabird in Norway is the puffin (Fratercula arctica), but its current breeding population of 1.25 million pairs is slowly declining. The kittiwake (Rissa tridactyla), however, is increasing and establishing new colonies; its population now stands at 510,000 pairs. The population of the common murre (Uria aalge), the seabird species most vulnerable to human activity, was about 160,000 breeding pairs in 1964 but is now decreasing at a rate of nearly 5% per year. Of the other alcids, the razorbill (Alca torda) and thick-billed murre (Uria lomvia) show similar declines, and the black guillemot (Cepphus grylle) is maintaining a stable population. The fulmar (Fulmarus glacialis) and the gannet (Sula bassana) have both spread from the British Isles and have established a number of breeding colonies in Norway during this century. Evidently immigration of gannets is still occurring, since the observed rate of increase far exceeds the population's intrinsic rate of increase. The impact of human activity on bird mortality varies from species to species. The two most serious factors are coastal oil pollution and the use of fishing gear; direct hunting pressure accelerates the decline of murres and razorbills. Persistent toxic chemicals are not yet a serious problem in Norway.