290 



E. BRUN 



Material and Methods 



The logistics of census operations have 

 gradually improved from the use of slow, local 

 transportation to the use of fast pneumatic 

 boats and, in more recent years, seaplanes. 

 Various census methods have been used, de- 

 pending on species and circumstances. 



For puffins, a method based on measure- 

 ment of feeding frequency and on the number 

 of puffins per time unit that pass a particular 

 observation post when they return from the 

 feeding ground was used (Brun 197 la). Kitti- 

 wakes and gannets were readily censused by a 

 combination of photographic methods and de- 

 tailed counts in sample areas (Brun 19716). 

 Direct counting is by far the most accurate 

 method for razorbills, murres, and fulmars; 

 but in the larger colonies of common murre, 

 lack of time permitted accurate counts for 

 only a limited proportion of the cliff. Direct 

 counts of individuals, the egg/chick ratio, and 

 estimates of the relative size of the censused 

 population were used to estimate the total 

 population of the colony. 



In a colony of kittiwakes near Troms0, envi- 

 ronmental factors that limit breeding success, 

 such as temperature and wind exposure, were 

 monitored throughout the breeding season on 

 a data recorder, and detailed measurements of 

 temperatures on and inside the eggs have 

 been recorded. For further information about 

 the influence of environmental parameters on 

 incubation rhythm and nest attendance, the 

 presence of the male and female at a par- 

 ticular nest was recorded by using radioactive 

 bands and a Geiger-Muller tube connected to 

 a pen recorder. 



In a study of the effects of human activity, 

 egg samples of selected species were analyzed 

 for mercury, PCB, and DDT derivates. An ef- 

 fort was also made to obtain figures for the 

 mortality caused by oil pollution and fishing 

 gear as well as by direct hunting pressure. 



Results 



Status and Trends of 

 Cliff-breeding Species 



Puffin (Fratercula arctica) 

 By far the most numerous seabird in Nor- 



COMMON PUFFIN 



Fratercula arctica 



1-10 pairs breeding 



11-100 



101-1000 



1001-10,000 



10.001-100.000 



100.001-1.000,000 



Fig. 1. Distribution of the puffin (Fratercula arctica) 

 in Norway. Numbers refer to localities listed in 

 Table 2. 



way is the puffin (Fig. 1), which is the only 

 species with a breeding population of more 

 than 1 million breeding pairs (Tables 1, 2). In 

 a 1964 census (Brun 1966) the total breeding 

 population was put at 1.5 million pairs. The 

 current figure of 1.25 million pairs includes 

 several newly discovered colonies and some 

 not censused in 1964; it is more accurate than 

 the previous census for most of the 15 largest 

 colonies which make up 99.9% of the total 

 population. The puffin population is concen- 

 trated in Troms and Nordland (94%), with 

 only about 3% in Finnmark. 



Kittiwake (Rissa tridactyla) 



The second most numerous seabird species 

 in Norway is the kittiwake, which dominates 

 in a number of the larger cliff colonies. Its dis- 

 tribution pattern differs from that of the puf- 

 finthe main occurrence of the kittiwake 

 population (about 63%) is in Finnmark 

 (Table 3). 





