Birds. 



8637 



rapid, appearing to have a sturdiness about it which is not observed 

 among the smaller owls. 



I am not acquainted with the changes which take place in the plu- 

 mage of those individuals which are kept in confinement, and even if 

 I were changes occurring under such circumstances would be regarded 

 with much caution. However, the examination of specimens of 

 different ages and sexes, obtained at various times of the year, has 

 enabled me to arrive at certain conclusions which I have recently had 

 opportunities of confirming in my visits to museums ami private col- 

 lections. 



It appears that the perfect plumage of the adult male is white, 

 without spot, but that this state is not attained until after the lapse of 

 several — perhaps many — years ; and also that in younger birds the 

 form, intensity and disposition of the markings are very little, if at all 

 influenced by sex. I believe that the adult female also becomes white, 

 having seen one very nearly in that state. Full growth is attained 

 about the end of the first winter, after which size is a reliable indication 

 of sex, a male seldom measuring more than twenty-three inches in 

 length, while twenty-six inches is the usual length of a female. The 

 younger the bird the more do the dark marks, especially upon the 

 under surface of the body, partake of a barred appearance, the sharper 

 are the edges and tips of the mandibles, and the broader and thinner, 

 although no less keen, is the projecting inner edge of the middle claw. 

 All of the claws are comparatively slender, and in colour resemble the 

 bill, being of a bluish or grayish tinge, while in the adult those parts 

 are black. Intensity of colouring has often been regarded as a mere 

 indication of advanced age, but this, taken by itself, is no criterion, 

 for at most times there is considerable variety of tint, even in the 

 same individual, and very dark brown or black is nearly always present 

 from the end of the first winter until some years afterwards. The 

 truth seems to be that in old birds the dark tints merely predominate, 

 and for this reason, — that as a general rule the lighter ones are the 

 first to disappear. And yet this is not invariably the case, for speci- 

 mens have been obtained which were perfectly white, with the exception 

 of a few faint bars upon the wings or tail. Upon the body spots are 

 usually darker than bars, and thus it is evident that the greater the 

 abundance of bars upon the body the younger is the bird. The size 

 of the spots probably decreases with age, and is said to be larger in 

 females than in males, but of this I have never yet been able to satisfy 

 myself. The parts in which the marks show the greatest inclination 

 to linger are the occiput, scapulars, wing-coverts, tertials, and more 



