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. Thompson, R. Tuxson This report summarizes at-sea observations by Smithsonian personnel during Leeward Island Survey 19, 23 May - 14 June, 1967. Excellent cooperation was received from officers and crew of the light tugs. 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 Laysan June 12, arriving in Honolulu June 15. Interisland and off shore (within 2 miles of land) observations are incomplete as preparations were being made for island landings. No collecting at sea was done on this survey. Loran and celestial fixes were used throughout the trip. Weather was generally good throughout the survey. In ten days (23-25, 26-28* 30 May, and 12 - 14 June), 82.4 hours of observations over 1054 diurnal miles were covered. During this period, 4623 birds of 19 species were recorded, after eliminating presumed duplicate sightings 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 observations 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 independent observers, i.e. one observer records a flock of Sooty Terns and Wedge-tailed Shearwaters that 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-day test period, observers on Vessel A saw two sea bird species not 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 be as significant as they appear. However, there remains a difference; * Partial days of observation.