66 
PACIFIC SCIENCE, Vol. XIV, January I960 
TABLE 4 
Population Densities of Sea Birds in the Sea Divisions Investigated 
COLD CURRENT 
OFF- 
SHORE 
SOUTH 
KURILES 
CONVER- 
GENCE 
WARM 
CUR- 
RENT 
PE- 
RIPH- 
ERY 
JAPANESE WATERS 
TOTAL 
OR 
AVER- 
AGE 
North- 
ern 
Sea 
Off the 
Kuriles 
Off 
Honshu 
( warm ) 
Off 
Kushiro 
( cold ) 
Number of days of navigation 
23 
7 
2 
1 
2.5 
2.5 
37 
Total number of birds observed 
4136 
761 
309 
160 
2699 
983 
9048 
Number of birds observed per day 
31-604 
39-281 
( average ) 
179.8 
108.7 
154.5 
160.0 
1075.6 
392.2 
345.1 
Number of birds observed per hour 
3-118 
5-46 
( average ) 
32.12 
17.55 
28.82 
21.42 
323.66 
71.66 
82.54 
20 
15 
11 
13 
15 
13 
37 
Number of species observed 
Av. 10.5 
Av. 5.8 
Av. 7.5 
— 
Av. 7.5 
Av. 6.6 
Av. 8.5 
decrease of O. fur cat a was recorded, but whether 
leucorhoa dominates furcata is not certain. It is 
to be added that on June 11, all of the birds 
( O . leucorhoa) were steadily moving eastward, 
which suggested a migration out of the most 
suitable temperature zone in accordance with 
some oceanic conditions. Thus, the range of 
temperatures recorded for leucorhoa was much 
greater than for furcata, while O. castro was 
distinctly a warm current species. 
O. furcata 
O. leucorhoa 
0. castro 
Air 
5-11.5 
3.5-22 
16.5-22.5 
tempera- 
Rarely 12-14 
Mostly 7-15 
ture, °C. 
A straggler at 
Especially 
21 
13-15 
Water 
3-8 
tempera- 
Once 11 
2.3-16 
10.8-16 
ture, °C. 
A straggler at 
Especially 
Rare at 8 
15.5 
6-8 
THE SHEARWATERS AND FULMARS: Puffinus 
tenuirostris and P. griseus showed distinct segre- 
gation to cold and warm currents respectively. 
The former was one of the commonest species 
in the northern seas, though it was rare off the 
Kuriles, but it was again found mixed with 
numerous griseus in warmer Japanese waters. 
The latter species was never found in the cold 
waters except for a few off Kushiro east of the 
convergence, but it was not seen on the off- 
shore true warm current surface. Other migrant 
southern hemisphere species, and the fulmars 
and the Japanese streaked shearwater (C alone c- 
tris leucomelas) , preferred the following tem- 
peratures. 
AIR 
WATER 
TEMPERATURE 
TEMPERATURE 
°C. 
°C. 
Puffinus 
6-11.5 
3.5-7 
tenuirostris 
A few 17-20 
A few 14.8-15 
P. griseus 
17-20 
11.2-12.5 
A few 7 
A few 8.2 
P. carneipes 
16.5-20.7 
10.8-16 
P. bulleri 
18.5-22.5 
14.5-16 
Calonectris 
leucomelas 
19-20 
12-12.5 
Pterodroma 
12-22.5 
7.5-16 
solandri 
Once 7 
Once 6.2 
Pt. inexpectata 
6.2-9 
5-6.2 
Pulmarus 
6-11.5 
3.5-7 
glacialis 
A few 17-20 
A few 14.8-15 
Synthliboramphus wumizusume was distinctly 
restricted to the warm currents, unlike all of its 
relatives, which are cold current birds. Cath- 
aracta skua, from the cool waters of the southern 
hemisphere, also was restricted to the warm 
current surface in this sea zone, while the arctic 
breeding skuas were found in cold currents, ex- 
cept for three individuals which were migrating 
across the warm current waters. 
