O^ ORNITHOLOGY. 425 



The " Stein " Eagle varies much in plumage, and in this 

 variation age plays an important part; but one transition and 

 three main forms of its plumage, and even of its build, can also 

 be clearly distinguished, and they are dependent on the loca- 

 lity of the nest from which the bird has flown. No stress 

 can be laid on the very variable size of individuals of all these 

 forms, for that is caused by alimentary conditions during the 

 youth of the bird. 



The south-west, north-west, and central European " Stein " 

 Eagles may be included in the first group, those of South- 

 eastern Europe in the second, and those that belong to the 

 north-eastern and northern parts of the continent in the third; 

 while between the second and third groups one finds an 

 intermediate, or what may be called a transition form. 



The third form is the Golden Eagle of the old writers Nau- 

 mann and Brehm, and so clearly and definitely do these great 

 naturalists describe it, that it can easily be recognized. It 

 exists, but what to call it, and whether to elevate it to specific 

 rank or not to do so, is the point on which the whole question 

 hinges. My own opinion is that as an individual species it 

 can no longer stand unless two more new species are to be 

 created, and then we should have three species of " Stein " 

 Eagles. For this the differences are too slight, for they are 

 not nearly so important as between Aquila imperialis and its 

 Spanish relative A. adalberti. That is why one speaks of forms 

 and not of species, for there is only one species of " Stein " 

 Eagle, but it is split up into three forms according to the 

 region in which it lives. As an example of this practice 

 with regard to many birds, I may instance the case of Halia- 

 etus albicilla. There is a great difference in size between the 

 Sea-Eagles of Northern and Southern Europe, but yet it 

 would never occur to any one to make two species out of 

 them. 



I have had fewer opportunities of observing the Imperial 



