F.B.KIRKMAN: VARIATION IN NESTS OF TERNS. 105 



once, and though they continued laying and re-laying 

 up to the middle of July, it is doubtful whether they 

 hatched out more than a dozen chicks. An almost clean 

 sweep was made of the eggs, the marauder being no other 

 than the humble rat. Traces of these creatures' feet and 

 tails were to be seen leading from nearly ever}^ nest to 

 the nearest tuft of bent, where the broken shells of the 

 eggs told the story of the theft. The deep narrow furrow 

 made in each case by the tail in the sand seemed to show 

 that the rat had used this appendage as a support while 

 it hopped along on its hind legs with the eggs clasped in 

 loving fashion to its breast. That it escaped being 

 murdered by the parents is remarkable. 



If the Terns had nested in the packed shingle of the 

 beach would their eggs have escaped the rats ? Arguing 

 a priori it is at least clear that they would have been much 

 more difficult to locate. Perhaps some other observer 

 can throw light on this point. 



So far I have shown, or attempted to show, that the 

 Arctic Terns are quitting the safer shingle site for others 

 more exposed. I suggest that this has been done with 

 comparative impunity (assuming the rat ravages to be 

 exceptional) owing to the greater scarcity of enemies 

 powerful enough to take advantage of the new conditions. 

 The same applies to a number of other sea-birds. Indeed, 

 it is more than likely that the extermination of the larger 

 birds of prey helps to explain much that is anomalous 

 in the habits of British birds. But to show that the 

 absence of enemies has rendered the change possible is 

 not to explain why it took place. It may be that, owing 

 to the spread of vegetation, or the invasion of sand, it 

 is the nesting sites that are altering their character, and 

 not the birds their choice. But this is mere conjecture. 



When we quit the subject of variation in site for that 

 of nesting material, we find ourselves face to face with 

 the two questions already put by Mr. Pycraft in respect 

 to the Ringed Plover, the first being : How comes it 

 about that certain individuals of the species provide 



