STERCORARIUS POMARINUS 



APRIL and MAY 1964-1965 



NOVEMBER 1964 - FEBRUARY 1965 



• 1 bird 



• 5 birds 



• 25 birds 



• 100 birds 



Figure 21. — Distribution of Pomarine Jaeger, spring migration months and winter months. 



During the summer and fall (May-October) 

 Pomarine Jaegers were nearly or completely 

 absent from the study area (identification of 

 the three birds recorded in September was not 

 certain). They began to appear in the area in 

 November , after their breeding season in Alaska 

 and Siberia. Numbers increased in December 

 and remained constant until March, except for 

 a possible decline in February. Monthly fluc- 

 tuations in numbers of this species, especially 

 during the winter (December-March), were as 

 much a reflection of the short period of obser- 

 vation in the bird's area of greatest density 

 (usually 2 half days per month, sometimes less) 

 as of actual increases or decreases in popula- 

 tion. The high total for April 1965 was prob- 

 ably the result of the presence in the area of 

 migrants from the south and Hawaiian Islands- 



based birds at the same time. By May most 

 birds had already begun their northward migra- 

 tion. 



Distribution : This species exhibits two distri- 

 bution patterns (fig. 21). During the winter 

 nearly all the birds (42 of 43) were within 50 

 miles of the Hawaiian Islands. In the months of 

 northbound migration (April-May) they were 

 still concentrated around the Hawaiian Islands, 

 but slightly more than half (47 of 91) were seen 

 farther than 50 miles from land. Observations 

 on the long. 148° W. leg accounted for fewest of 

 these migrants (only 2 of 47). 



Either the birds returned from their breeding 

 areas during the period the ship was in port, or 

 a different route was used. 



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