PRESENT STATUS AND TRENDS OF SEABIRDS IN NORWAY 



291 



Table 1. Estimate of the numbers of seabirds breeding on the coast of Norway 1970-1974. 

 Species are listed in descending order of breeding population size. 



a Numbers in parentheses are not based on a complete census of the coast. 

 b ln addition, an unknown number of pairs breeding inland. 



The annual production of kittiwakes shows 

 enormous variation, both throughout the 

 coastline and in different years; however, at 

 our sample stations in north Norway, the 

 mean production in 1974 (Table 4) was more 

 stable and was near the minimum value neces- 

 sary to maintain zero population growth. 



This minimum production, m x (number of 

 females produced per breeding female), can be 

 computed from survival rates 



m x = (1-P)/1 X = 0.13/0.57 = 0.23 



where P is annual adult survival and l x is sur- 

 vival of fledged chicks up to first breeding. 

 Data on survival are taken from Coulson and 

 White (1959) and from Norwegian banding 

 recoveries. 



The kittiwake has, however, established a 

 number of new colonies, and although the 

 local increase in some of these is spectacular, 

 the long-term change during the last 15 years 

 is only about 1% increase per year in northern 

 Norwegian colonies (E. Brun, unpublished 

 data). In southern Norway, the population 



has increased much more rapidly (Brun 

 1971c). 



Common murre (Uria aalge) 



The common murre (Fig. 2) has shown a 

 considerable decrease. The most spectacular 

 decrease is at S0r-Fugl0y, where a colony of 

 10,000 pairs in 1940 was reduced to 4,000 

 pairs in 1961, to 1,100 pairs in 1966, and to 

 only about 10 breeding pairs in 1974 (Table 5). 

 Most of the census work was done in 1964 and 

 1974. The general trend in population change, 

 as expressed by the yearly decrease or in- 

 crease, has been extrapolated forward to 1974 

 or back to 1964 for those colonies where cen- 

 suses were missing for either of these years, to 

 enable a better comparison (Table 6). The 

 overall decrease in Norwegian colonies of the 

 common murre is, thus, near 5% per year; the 

 few cases with a positive trend are based 

 either on very small figures or on extrapola- 

 tion from old, inadequate censuses. 



Thick-billed Murre (Uria lomvia) 

 The thick-billed murre (Fig. 3) was first 



