342 
PACIFIC SCIENCE, Voi XXI, July 1967 
Fig. 17. Abundance, distribution, and movements of murres ( 10-minute counts only). Abundance is in- 
dicated by length of vector and, when not in flight, by numbers at the point of observation. The number is 
printed on the vector when more than 100. C indicates circling; X indicates that the birds were on the water. 
Cape Lisburne {top) and Cape Thompson colonies are indicated by cross hatching. 
1-5 
6-10 » 21-30 - 
11-20 » 31-50 - 
ing intervals. Although distinguishing the two 
species was difficult unless the birds came very 
close to the ship, it appears that away from 
the colonies at Cape Thompson and Cape Lis- 
burne (in general, 5 miles offshore and be- 
yond), Thick-billed Murres greatly outnumber 
the Common Murres, probably making up more 
than 90% of the murre population on the open 
ocean. On the nesting cliffs, the population is 
believed to include 60% Thick-billed Murres 
(Swartz, 1966), implying that Common Murres 
prefer shallower water than do thick-bills. This 
is consistent with data on food habits (Swartz, 
1966), which imply that Common Murres feed 
in shallower water. The area on the open ocean 
in which the fewest murres were seen was near 
the ice pack at about 70°50 / N, 166°0Q'W. 
» 51_80 
» 81-100 — » 
The greatest number of murres was found 
within about 40 statute miles from the nearest 
colony (Fig. 16). It is apparent from Figures 
16, 17, and 18 and from direct observation of 
feeding activities made from the ship that the 
usual feeding activity of breeding birds takes 
place within about 40 miles of the nesting 
cliffs and mostly within about 30 miles. Since 
murres are strong flyers and are capable of fly- 
ing at least 50 mph (Vaughan, 1937:123; 
Baxter and Rintoul, 1953; Portaz, 1928; Frow- 
hawk, 1928, in: Tuck, 1960:23) s a feeding dis- 
tance of 30-40 miles seems reasonable. Feeding 
areas for the Cape Thompson colonies seem 
to be primarily south of Point Hope, and those 
for the Cape Lisburne colonies north and west 
of the Cape Lisburne cliffs, although some over- 
