316 
On the Nest and Eggs of the Common Tern 
TABLE VII. 
Type u f Nest a nd Colour: 
Type of Nest. 
C 
Totals 
Brown 
63 
376 
439 
Green 
79 
590 
669* 
Totals 
142 
966 
1108 
■ One ' slatey grey ' egg and one ' blue ' egg had to be omitted from this table. 
We find for tetrachoric r 
r= + -0745 ± -0409. 
This cannot in itself be considered significant. The sign indicates that green 
egg-layers make the more elaborate nests. No stress can, however, be laid on the 
result. 
We now take mottling and type of nest using the arrangement below as the 
best order we could devise of decreasing mottling. 
TABLE VIII. 
Mottling and Type of Nest. 
Categories of Mottling. 
Type of Nest 
d 
e 
a + b 
k 
/' 
i 
Totals 
1 
39 
10 
7 
58 
5 
20 
3 
143 
c 
1.5 
198 
71 
61 
430 
24 
135 
31 
965 
Totals 
16 
237 
81 
68 
488 
29 
155 
34 
1108 
The method adopted was that of ' biserial 77 ' with class index correction for the 
mottling categories. We find, the class index correlation being "9534, 
Correlation = + -1141 ± -032.5, 
the sign indicating that the finer blotches are associated with the more elaborate 
nests. 
* The preponderance of green eggs over brown in the ternery at Blakeney Point deserves con- 
sideration because it has not always been recognised. H. Seebohm, Eggs of British Bird<, London, 
1896, writes that the eggs " vary in ground colour from pale greyish-bufi to brownish-buff, occasionally 
with a tinge of green" (p. 102). F. O. Morris, Natiinil Iliston/ of the NcH^ rnid Eggs of British Birds, 
London, 1892, gives a wider range of colours, "pale blue, pale yellow, green, brown, white or light dull 
yellowish or stone colour" (Vol. iii. p. 136), which certainly does not emphasise the broad alternative 
categories brown or green, with a fractional percentage of blue or grey. 
