it represents 24 o/o of the total species recorded by Vessel B. This percentage figure makes the difference appear too significant unless the observer is interested in every possibility of species occurrence. If so, in this case two independent observers did not record the same species. Why did not both observers record all of the same birds? It is a matter of distribution. An example: If we use a three foot square sample plot and spread, randomly, 30 red and 30 blue marbles and two green and two yellow marbles on this sample plot, any two similar transects will probably sample representatively the common marbles (red and blue) but probabilities are slight that both transects will sample the uncommon marbles (green and yellow). Thus it is with sampling bird populations. Both observers record representative numbers of common birds species, but uncommon species of low density may not be recorded by both observers. Secondly, there is variance between observers. Observers vary in quality, but perhaps more important, individual observers vary through time. Extended periods of observations "dullen" an observer. Two observers on duty can, and often do, cause mutual distraction and at times an observer may not fee up to normal. All of these lessen the uniformity, and hence the quality of the observations. In species accounts that follow, species totals for the cruise include, for the periods duplicate observations, only the observations from Vessel A. Laysan Albatross 31 Low albatross numbers are believed to result from recording techniques used for ship followers. By convention, only the daily high numbers are recorded as daily totals (This assumes that the ship followers accumulate during the day). Albatross do not follow for extended periods the small vessels used on this survey. Hence, the totals recorded are low and not indicative of actual densities. One concentration of 16 birds was recorded on 30 May between Midway and Pearl and Hermes. Black-footed Albatross 72 The greater number of this species recorded over Laysan Albatross probably indicates this species' greater tendency to follow ships. These numbers are low for reasons outlined in the preceeding account and are believed not to reflect actual densities. Wedge-tailed Shearwater 1766 Ten dark phase birds were recorded, primarily in the main Hawaiian Islands. Only one dark phase bird was recorded in the western leeward island area. Dark phase birds were also uncommon among the breeding populations present in the western leeward islands. This species represented 38.2°/o of total birds observed. They were found commonly in feeding flocks as usual. Buller Shearwater 1 One bird was recorded on 30 May at 28° N, 177°18' W. Sooty Shearwater 4 Only four birds were recorded. Three of them were in the main Hawaiian Islands and one recorded between Midway and Pearl and Hermes Reef.