A Cooperative Shrdi/ 317 
Lastly we turn to the intensity of the ground colour and the type of nest. 
Here we have worked independently brown and green eggs and the results are 
given in Tables IX and X. 
TABLE IX. 
Ti/pe o f Nest and Density of Colour, in Brown Eggs. 
Density of Colour. 
Type of Nest 
A, 
c. 
Di 
Z^i + /i + A', 
T(,tals 
S ... 
15 
11 
5 
12 
8 
6 
6 
63 
c ... 
39 
65 
58 
83 
43 
38 
50 
376 
Totals 
54 
76 
63 
95 
51 
44 
56 
439 
Again we use the ' biserial rj ' method and correction for class index corre- 
lation (-9785) ; we find 
Correlation = + -2189 ± -0481. 
Thus there is significant, if only still very moderate, correlation, the relation- 
ship being between denser brown ground colour and the simpler nests, i.e. holes in 
the ground. 
TABLE X. 
Type of Nest and Density of Colour in Green Eggs. 
Density of Colour. 
Type of Nest 
-^2 
B., 
Z», 
E, 
0., 
ff. + l. + K., 
Totals 
3 
5 
14 
10 
12 
6 
15 
14 
79 
c 
31 
46 
57 
123 
73 
79 
54 
127 
590 
Totals 
34 
51 
71 
133 
85 
85 
69 
141 
669 
Using the same method as before (class index correction "9860), but with one 
more category as and (?, could be separated as their total was more consider- 
able, we have 
Correlation = - -2366 + -0407. 
Thus the dark tones of green are on the whole more frequently associated with 
the nests to which material is brought. 
Accordingly in the case of both ground colours, although we cannot definitely 
assert that either brown or green egg-layers are the more elaborate nest builders, 
we can assert that the denser brown and lighter greens are somewhat more usual 
when the nest is a mere hole in the shingle, and that the lighter brown and 
darker green eggs are associated with more elaborately constructed nests. Again 
the larger blotches are in somewhat greater proportion to be associated with 
unelaborated nests and the finer mottling with the elaborate nests. There is no 
