12° N. 
12 January; 2 6 February; 13 March; 27 April 
$■ Miles = 423 
$ Days = 4 
// Species = 11 
Linear 
Density = 1.4 
Species 
Sooty Tern 
Pterodroma ext erna 
, ___ ——— 
Bird sp. 
Misc. Shearwater/Petrel 
Wedge-tailed Shearwater 
Red-footed ^Booby 
Pterodroma sp. 
Bulwer Petrel 
Blue-faced Booby 
White-tailed Tropicbird 
Red-tailed Tropicbird 
Newell Shearwater 
Small Pterodroma 
Booby sp. . 
Storm Petrel 
Shearwater sp. 
Percent Number 
56.1 
329 
9.6 
56 
8.5 
50 
6.7 
39 
3.6 
21 
3.4 
20 
3.2 
... 49 
1.7 
- 10 
1.7 
10 
1.4 
8 
1.0 
6 
0.9 
5 
0.7 
4 
0.7 
4 
0.7 
4 
0.2 
1 
100 586 
A consistent area of increased bird activity characterized by: 
l) Sporadic flocks of Sooty Terns; 2) Flocks of Pterodroma externa and 
other Shearwaters and Petrels; 3) Low relative numbers of Wedge-tailed 
Shearwaters; 4) Red-footed and Blue-faced Boobies (December to March); 
5) White-tailed Tropicbird. All the characteristic bird elements con¬ 
sistently show a decrease in density immediately to the north and south. 
The area is not broad and could be completely traversed over night (as 
probably occurred in February and possibly in April). On the 12th oi 
March, en route to Kingman Reef, the birds showed a slight indication of 
increase in the late afternoon. The next morning, before 0900, 97 percent 
of the day's total of 122 Shearwaters and Petrels, and y4 percent 01 uhe 
day's total birds were logged. This peak was abruptly followed by a re¬ 
turn to very low density for the remainder of the day (see Graph fr3)« 
Taking sunset of 12 March as marking the approximate north edge of the 12° 
zone, and noon of the 13th as its south edge, the '12 N. area during 
mid-March at l60° W. is about 120 miles wide between 13°40' and llVO' N.^. 
In January, near l66° W., the zone again appeared to be centered 6 >j 0 u. N. 
SIC data suggest that in April the zone lay farther south between 9°30' N. 
and H°30'N. and that it may have been somewhat broader. (See BT discussion.; 
12° N. to 5° N. 13 January; 25 February; 26 April; 14 March 
# Miles of obs. = 397 
# Days of obs. = 4 
# Species • = 17 
Linear density «= .458 
