Ped-footed Booby Estimated population - : 435 +, 10% 
(Sula sula) Estimated breeding population -: 60 £ 10% 
—— Estimated roosting population-: 375 + 10% 
Nest count: total nests counted -: 25 
Nests with eggs--—--• 0 
Nests with downy young-: 25 
Estimated % nest count complete -—: 85% 
Berlese samples taken -: 5 
Sera samples collected-*-* 25 
Number of returns-— • 47 
Number banded--—• 27. 
The nest count for August, 1966 does not markedly differ from that 
taken in July except in that a larger proportion were on young on the 
latter visit# The increase in total population from July is the result 
of an apparent increase in the number of roosting birds# 
The proportion of roosting birds including both those returned and 
those newly banded was broken down by age-class# Ten of 57 (17*5%) 
roosting birds handled were immatures; 37 of 57 (65*0%) were subadults, 
and the remaining ten (17*5/0 were adults# The return data on the 
roosting subadults (n=21) indicated that about 48% of these birds had 
been banded on Enderbury Island# Since the total T!ed-footed Booby 
population on Howland was composed of about 86% roosting.birds and, 
since subadults comprised 65 % of the roosting population, then it 
follows that roosting subadults from Enderbury comprised not less than 
26 to 28% of the total Howland Ped-footed Booby population# The 
comparative figure for July,1966, calculated in the same manner, 
was 27% suggesting that a fairly consistent proportion of the summer 
population is from or has been on Enderbury# 
On the July,1966, visit to Howland 20 nests with eggs were marked 
with colored, elastic, pressure sensitive tape as part of a month 
to month nest check designed to determine the incidence of failure in 
early stages of nesting# Only 11. of these markers were found in 
August# Of the 11 nests re-found on the second visit only five still 
held contents (four with chicks and one with an egg.) Four of the other 
nests were empty and two had vanished completely# The incidence of 
nest failure at the egg or small chick stage (on an admittedly small 
sample) was no less than 55%• 
Possibly the relatively high disturbance was caused by predatory 
activities of frigatebirds directed at eggs, small chicks, or nesting 
materials# 
