Sea Bird Distribution — KURODA 
63 
TABLE 3 
Analysis of Population Densities and Patterns of Chief Species of Sea Birds in the 
"Northern Sea Divisions,” 12 June-5 July 1954 
NUMBER OF INDI- 
OC- 
CUR- 
LOW- 
EST 
ECONOMIC DENSITY 
VIDUALS PER HOUR 
SPECIES OF BIRDS 
Variation 
Mean 
S.D. 
(6) 
Modef 
Mean 
RENCE 
RATEt 
DEN- 
SITY 
Fulmarus glacialis 
0.3-12.2 
*32.9-76.2(5) 
12.86 
19.0 
1.4-3. 2 
2.43 
1.00 
12.86 
Puffinus tenuirostris 
0.3-17.8 
*46.6-60.8(3) 
13.69 
18.0 
1.2-3. 7 
2.19 
0.91 
12.45 
Oceanodroma fur cat a 
0.1- 4.6 
*40.0 
3.07 
8.0 
1. 1-2.3 
1.58 
1.00 
3.07 
0. leucorhoa 
0.1- 4.0 
0.73 
0.9 
0. 1-0.4 
0.28 
0.56 
0.41 
Lunda cirrhata 
0.1- 3.7 
1.46 
1.0 
1. 1-3.7 
2.18 
0.91 
1.33 
Uria spp 
0.1- 2.1 
0.55 
0.6 
0. 1-0.2 
0.20 
0.56 
0.31 
Aethia psittaculus 
00 
1 
r-H 
o 
1.00 
1.5 
0. 1-0.6 
0.43 
0.34 
0.34 
Rissa brevirostris 
0.1- 6.5 
1.92 
1.9 
0.2-2.7 
1.90 
0.47 
0.90 
R. tridactyla 
0.1- 2.0 
0.73 
0.6 
0. 1-0.2 
0.13 
0.52 
0.38 
Stercorarius longicaudus 
0.1- 1.8 
0.39 
0.4 
0. 1-0.3 
0.16 
0.52 
0.20 
* Indicates concentrated or "highest’’ density: 5 cases in Fulmar us, 3 in P. tenuirostris, and 1 in O. jurcata. These are 
included in the means. 
t The mode indicates most frequent densities, exclusive of unusual or "highest’’ densities. 
$ Occurrence rate is the ratio between the number of days the species occurred and the total of 23 observation days. The 
lowest density is the mean economic density X the occurrence rate. 
phere migrants as Pterodroma solandri and 
Puffinus hulleri (first recorded )\wei i e common, 
and a few Puffinus carneipes and Catharacta 
skua occurred, while Synthliboramphus wumizu- 
sume reached there from its Japanese breeding 
waters. 
D. Japanese Waters C 
1. Warm waters off Honshu 
The oceanic conditions are similar to area 
C above, but the water temperature was lower 
(12°-13° C.), and cold and warm currents 
were distinguished at about the latitude of 
Cape Erimo, Hokkaido. D. nigripes became 
common south of that latitude and P. car- 
neipes, O. castro, and Catharacta skua oc- 
curred, while a few Fulmarus and a single 
straggler of O. jurcata were seen south to 
143° 42' E, 41° 23' N. Two Fulmarus were 
sighted as far south as Iwate, Honshu. The 
coastal waters of Sanriku (N. Honshu), where 
currents meet and which are rich in food sup- 
ply, were the main summering grounds of 
Puffinus griseus. Nearer to the coast, some 
2,000 Calonectris leucomelas were observed 
off Yamada Bay, apparently over a shoal of 
sardine; P. griseus, with a weaker bill, prefers 
to feed upon euphausids. These two species 
were responsible for the very high population 
density of this coastal zone. 
2. Cold waters off Kushiro, Hokkaido 
In this southern limit subdivision of the 
cold northern waters, Fulmarus and P. tenui- 
rostris were again numerous and Lams schis- 
tisagus and Brachyramphus marmoratus oc- 
curred in coastal waters. 
CORRELATION WITH FOOD SUPPLY 
The abundance of plankton, a basic food sup- 
ply of sea birds, is correlated with local up- 
wellings of the sea which are caused by sea bot- 
tom conditions (especially near islands), and 
currents as well as winds. A special study of 
