- 2 - 
it represents 2k o/o of the total species recorded by Vessel B. This percent¬ 
age 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 37 
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 tollowers 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 probab¬ 
ly 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 Yj66 
Ten dark phase birds were recorded, primarily in the main Hawaiian 
Islands. Only one dark phase bird was recorded in the western leeward is¬ 
land area. Dark phase birds were also uncommon among the breeding popu¬ 
lations present in the western leeward islands. This species represented 
38.2°/° 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 ^ 
Only four birds were recorded. Three of them were in the main Hawaiian 
Islands and one recorded between Midway and Pearl and Hermes Reef. 
