126 BIRD WATCHING 



Questions of this nature might be settled in the 

 future on facts observed now, as easily as a reference 

 to an iron ring where boats were once moored settles 

 the question as to whether the coast has risen or 

 the sea encroached. The coast and the sea, however, 

 remain. Birds, slaughtered by millions each year, 

 must cease almost as a class before any great period 

 has gone by. Of what use then the ring, the record 

 when what it speaks of is no more? 



Another interesting point in the Arctic skua (which 

 it shares with at least one other species of the genus) 

 is its dimorphism — or rather, to describe it more 

 properly, its polymorphism. To me it seems to offer 

 a case of a species in course of variation from one 

 form into another. In the two extreme forms the 

 plumage is, respectively, either entirely sombre both 

 above and below, or the whole throat, breast and 

 under surface, with a ring round the neck, and more 

 or less of the sides of the head, is of a fine cream 

 colour. Between these extremes there are various 

 gradations, the cream being sometimes on the breast 

 only, whilst the throat is of a lighter or deeper grey, 

 more or less mottled with the still darker shade, or 

 the lighter colour is hardly or not at all discernible 

 on these parts, whilst lower down it becomes less and 

 less salient till it is merely a not so dusky duskiness. 

 The cream-coloured birds, though numerous, are in 

 the minority, and both this and their being much 

 handsomer suggests that the process of change is in 

 this direction, whilst the intermediate tintings may 

 represent the steps in this process. To what form 

 of selection (if to any) are we to attribute the change? 

 As the cream colouring makes the bird more con- 



