318 
On the Nest and Eggs of the Common Tern 
reason to believe in any appreciable difference in volume of the simple nest and 
the complex nest eggs, but the former differ somewhat in shape from the latter, 
being broader and shorter, i.e. the eggs in mere holes are more rotund and in the 
elaborate nests more ovaloid. 
Although none of these characters appear to be litg lily correlated with the type 
of nest as determined by the simple alternative categories adopted by the field- 
workers, yet they are of a nature which more or less lend themselves to explanation 
on the basis of a protective colouring. It is not possible to determine whether 
the great variety of colouring and mottling in the common tern's egg is a vestige 
of an elaborate system once developed for protective purposes, and now falling 
into disuse, or, as a product of physiological causes, it is now being slowly adapted to 
protective purposes. The problem is a very interesting one and further light we 
think might be thrown on it, if a fuller record were in future to be made of the 
immediate colouring of the nest, — the colour of the materials out of which it 
is made, and in the case of holes the colour of the ground, shape and nature and 
colour of the adjacent pebbles or shingle. It would mean much additional labour, 
but considerable information bearing on the points discussed above might arise 
from such data. 
(4) Tlie Problem of the Mixed Colour Clutches. 
We propose in this section to discuss the problem of the mixed colour clutches. 
The following are the data to be analysed : 
TABLE XI. 
Colour Composition of Clutches. 
Size of 
Clutch 
Number 
Colour Composition 
Number 
of Eggs 
1 
2 
3 
4 
138 
- ■ 178 - - 
204 
1 
74 5 + 63 6' + l.S'(? 
m B^-irlQBGJrmO-^ - - 
138 
- . 356 - 
62 £3 + 8 BHl + 1 4 ^r/'i + 1 1 9 CP + 1 BL 
O B^ + 0 BHj + 0 B'-W- + 0 /?6'3 + 1 
612 
4 
Totals 
521 
203 B only, 41 composite, 275 G only, 2 anomalous 
1110 
B 
"■=^H brown, 6'"'=?/i green, (SG-' = slatey-grey, 5Z = blue egg 
Putting aside the two anomalous eggs, we have 41 clutches out of 519 wherein 
brown and green eggs are mixed. Putting aside the clutch with 4 green eggs we 
see that as a whole there are 
443 brown eggs to 659 green eggs, 
* The blue egg may be accounted for by the oxidisation of a green egg — a phenomenon observed by 
Newton (A.rt. ' Birds' Eggs,' Encycl. Brit.) ; the origin of the oxidisation being unrecognised in this case. 
Newton also states that the individuals of some few species of birds do not always lay eggs of the same 
ground colour, but the source indicated by him, i.e. change with age of bird, would not apply to our case. 
