5 ^ 
Diurnal bird observations were divided to correspond directly and 
simultaneously with the BT drop and position. Abundance and occurrence 
are expressed in units/hour. The nominal data plotted in Graph 4 is 
species/hour and sightings/hour. I maintain that these two statistics 
are zhe most accessible and general measurements that apply to nonrandom 
bird abundance in a spatial reference system. Thus in the same manner as 
the BT data the two statistics were fit to a proportionally equal scale 
and graphically added -- giving the curve in Graph 6. It is of interest 
to note that while neither sightings/hour nor birds/hour alone plot out to 
a smooth curve, artificial summation of the two gives a remarkably smooth¬ 
looking curve. I take this as an indication that the birds-plus-sighting/ 
hour manipulation is a more valid presentation of abundance data than 
either single parameter. 
In Graph 6 the bird concentration appears to be associated with a 
flat plateau-like section of the deep-water curve. This is perhaps best 
interpreted as being a set of two parallel "ribbons" of rapidly moving 
current at points .C^ and C 2 • The section between these ribbons is evi¬ 
dently a relatively non-motile water mass with a fairly high degree of 
turbulence and eddying effects. 
A consistent but puzzling thermal pattern is found in both the 12° N. 
and the 5 ° N. surface temperature structure. Although the surface tem¬ 
perature shows increase in the entire breadth of the zone the plot is 
not a smooth or normal curve but is slightly saddle-shaped, with the 
highest temperatures at the north and south edges, and a shallow less 
warm valley in between. This is easily noted for the March 12° data 
(33) and less easily seen for both areas in the April Data (4 A & 3, 
7 A & B, 6 A & B). The effect is fairly small but I think it is real and 
relevant. A surface temperature recording thermograph keeping running 
temperatures would quickly disclose its bearing on bird distribution. 
BT casts taken during the operations in the center of the 5 ° zone 
were in some cases only several to a score of miles apart latitudinally 
( 4 c). The ragged look of this section of the graph was at first thought 
to be a random sort of thing that would appear whenever casts were made 
this close together. However, in one section that was covered three times 
in the course of one day the variations were found to be reproducible and 
in fact the horizontal north to south rate of change was very large — 
easily measurable changes occurring inside of 10-15 miles. This may in¬ 
dicate a' degree of turbulence resulting from current velocity. I hope 
some light will be shed on these problems by someone with experience in 
interpretation of BT data. 
During April it appears that the 12° N. activity area was crossed at 
night (6 d). Based on March observations, a bird density peak about half 
of zhe recorded April "6° N." peak could have been expected over this 
section. 
Certain pertinent species have been plotted against the April thermal 
data, and several additional manipulations of the April data have beer, 
graphed. The bird distribution plots will be discussed in the species sec¬ 
tion but the graphs, Nos. 8, 9> and 10 are adjoined here with the BT and 
general bird information for the sake of easy comparison. 
/ 
