Leewards Island Survey $ 19 
Preliminary Report, At-Sea Survey 
May - June 1967 
Personnel: D. L. Burckhalter, R. L. DeLong (BIC), D. L. Stadel, F. C. Thomp¬ 
son, R. Tuxson 
This report summarizes at-sea observations by Smithsonian personnel 
during Leeward Island Survey 23 May - 14 June, 1967* Excellent coopera¬ 
tion was received from officers and crew of the light tugs. 
1 
After departing Honolulu May 23, a stop was made at French Frigate Shoals 
to disembark personnel (Amerson and Lewis) and their gear on 25 May. On 26 
May, Gardner Pinnacles was visited and on 28 May a stop was made at Pearl 
and Hermes Reef. From there the vessels proceeded directly to Midway Island 
for refueling, and returned to Pearl and Hermes on 30 May. The vessels 
moved to Lisianski June 1-2, moved on to Laysan June 6-7, and departed Lay- 
san June 12, arriving in Honolulu June 15- 
Interisland and off shore (within 2 miles of land) observations are in¬ 
complete as preparations were being made for island landings. No collecting 
at sea was done on this survey. Loran and celestial fixes were used through¬ 
out the trip. Weather was generally good throughout the survey. 
In ten days (25—25, 26* i -28f 30' 5 May, and 12 - 14 June), 82.4 hours of 
observations over 1054 diurnal miles were covered. During this period, ^623 
birds of 19 species were recorded, after eliminating presumed duplicate sight¬ 
ings from the two ships. Simultaneous observations were conducted from two 
ships during 5 days (24 - 28 May) of the outbound leg, totaling 40.8 hours 
and covering 421 miles. The vessels were side-by-side and separated four 
miles to test the basic assumption that two independent observers traveling 
the "same" track will see the same birds. On the return trip, diurnal obser¬ 
vations were shared 'by the two vessels with the observing vessel always in 
the leading position. These separate observations were then lumped to give 
daily totals. 
* 
Discussion: By using identical vessels and operating over the "same" waters 
at the same times, we have eliminated many of the variables encountered in 
comparison of at-sea observations taken at different times, under varying 
conditions. 
As can be seen from table 3, daily totals show large variances between 
observers on the two ships. The large discrepancies generally lie in the 
number of flocks seen by the independant observers, i.e. one observer records 
a flock of Sooty Terns and Wedge-tailed Shearwaters uhat is not visible 
to the other observer, thus increasing his total birds well above the other 
observer. 
Probably more comparable is the number of species seen each day by the 
two observers. As seen from table 3, this number does vary between observers. 
During the 5-hay test period, observers on Vessel A saw two sea bird species 
net recorded on Vessel B, and Vessel B recorded four sea bird species and two 
accidental species not recorded by Vessel A. These non-mutually observed 
species were usually a single sighting of sometimes a few birds, thus may not 
oe as significant as they appear. However, there remains a difference; 
* Partial days of observation. 
