262 BRITISH BIRDS. [vol. vm. 



if two eggs are found in one clutch with the ground- 

 colour completely different, the eggs could not have been 

 laid by one and the same bird. To prove this theory 

 definitely, it seems to me one must induce birds to lay in 

 captivity, or else keep watch on a laying bird. This is 

 possible only if the bird has some distinctive identification 

 mark, e.g. one bird we watched had a white spot on the 

 upper mandible on the left side. But how often can one 

 put either of these two methods into practice ? Practi- 

 cally never. Personally I am convinced that one bird 

 can produce eggs of different colour. Supposing that a 

 clutch of eggs of various colours has been laid by more 

 than one bird, the inference is that the bird lays its 

 eggs anywhere. Then why are clutches of four so 

 exceedingly rare ? Surely under the circumstances they 

 should be frequent enough. Yet the only clutch of 

 four we have found on Blakeney Point (July 1914) was 

 without doubt laid by one bird. The measurements 

 were : Length 4.45, 4.45, 4.55, 4.56 cms. Breadth 3.00, 

 3.05, 3.05, 3.09 cms. The ground-colour of all four was 

 identical. The mottling came under one type (C) of 

 our scale of mottling. This is convincing enough to 

 anyone acquainted with the extraordinary variabihty 

 of the eggs of this bird. The most conclusive proof of 

 this theory I have had was a clutch of three eggs, found 

 near the Tern Dunes in the same month as the above. 

 The measurements are these : Length 3.31, 2.56, 3.66 cms. 

 Breadth 2.86, 2.89, 2.90 cms. All three were quite 

 different, both in ground-colour and mottling. Now 

 the average length of egg at Blakeney is between 4.30 

 and 4.50 cms. Is it possible that three different birds 

 laid the three smallest eggs, out of a total of 1,117 that 

 we found and measured, in one nest ? It might be a 

 coincidence, but it would be a miracle at the same time. 

 Extremes in size for the last two years are : 



1913. 1914. 



Largest 4.70 4.86 cms. 



Smallest 3.60 3.31 „ 



