AND BLACK-BILLED AUK. 
13 
The opinion which I hold regarding the Colymbus Mi- 
nor and Aica Pica is, that they are merely the young, or 
the old in winter-plumage, of the two species Colymbus 
Troile and Alca Torda, the Foolish Guillemot and Hazor- 
Bill. Many ornithologists have maintained that they are 
separate species, but as Montagu has included all that 
has been a;dvaneed for this opinion, I shall examine chiefly 
what he has stated on this subject. 
It has been insisted on as a very strong circumstance in 
favour of the distinction of the two disputed species, that 
they are uniformly inferior in size and length of bill to 
those which are maintained to be their respective species in 
a state of maturity ; but even if this difference of size were 
admitted, it could not be of any weight in specific distinc- 
tion : — it is very inconsiderable, and very varying, and can 
be observed only for a limited time ; for, according to 
Montagu, we can have an opportunity of seeing these 
species of Lesser Guillemot and Black-billed Auk only 
during the winter months. Is it not very natural to anti-= 
cipate that the young should not attain the full size of the 
parent birds for some time ? Inferiority of size, therefore^ 
should rather be a presumption against the opinion of their 
distinction. But, as far as my observations go, there is na 
uniform difference of size ; they are fully as often to be 
met with equal in size as inferior ; and even individuals of 
the C. Troile and A. Torda often materially differ in this 
respect. This irregularity may chiefly be attributed to in- 
equality in their supplies of food, to which they must often 
be exposed in their earlier age, when the tendency to per- 
manent size is impressed, — from the habit of prematurely 
committing themselves to a boisterous and capricious ele- 
ment, and, consequently, often being separated from the 
protection of the parent birds. 
