% 
expectedly, direct reflections of the populations using the island. Dif¬ 
ferent species vary, however, in how the offshore observations can be used 
as a yardstick to estimate the island population. That is to say, the 
ratio of species observed offshore is not always the same ratio iound dur¬ 
ing the island census. Below is an arbitrary scale which is an attempt to 
express this situation. Blue-faced Booby is here taken as a standard on 
which to relate other species. The arbitrary ratio, 1:10, for Blue-faced 
Booby is defined as: for .every Blue-faced Booby observed during a few 
hours' cruise around an island, from 2-7 miles distant, ahout 10 Blue-faced 
Boobies will be found utilizing (roosting or breeding on) the island. 
Sbecies 
Ratio Approximation 
Wedge-tailed Shearwater 
Christmas Shearwater 
Audubon Shearwater 
Phoenix Petrel 
White-throated Storm Petrel 
Red-tailed Tropicbird 
Blue-faced Booby 
Brown Booby 
Red-footed Booby 
Frigatebird 
Shorebird 
Gray-backed Tern 
Sooty Tern 
Blue-gray Noddy 
Common Noddy 
White-capped Noddy 
White Tern 
1:125 
1:225 
1:250 
1:150 
1:200 
1:20 
1:10 
1:40 
1:50 
1:10 
1:20 
1:100 
1:100 (eggs) to 1:20 (chicks) 
1:125 
1:50 
1:75 
1:30 
Tutuila. American Samoa 8 & 12 April 
Approaching and leaving Tutuila on the north side, large feeding 
flocks were encountered as has been noted on previous cruises. Sometimes 
uhe flocks are within 10 miles or so of the island and are best considered 
offshore-type observations. The following is a hypothetical 5>-count mat 
might be obtained with some concentrated offshore observations at ca. 5-15 
miles. Sooty Tern is usually absent. 
Soecies 
. ... ■— 
Common Noddy 
White-capped Noddy 
Rea-footed Booby 
W T hite Tern 
Wedge-tailed Shearwater 
White-tailed Tropicbird 
Small Pterodroma 
• Brown Booby 
Sooty Shearwater 
Audubon's Shearwater 
Tahiti Petrel 
Shorebird 
/ 
/ 
5) Estimated (Idealized) 
15 
30 
8 
6 (sometimes more) 
5 (or more) 
3 (sometimes more) 
1 
Less than 1 
Less than 1 
Less than 1 
Less than 1 
Less than 1 
(ca. )"l00 
