CIRCUS SWAINSONII, 
food consists of small quadrupeds, birds, reptiles, &c. and upon some one or other of these it is 
often to be seen pouncing in the course of its flight. Damp and marshy situations appear 
to form its favourite hunting grounds, but it does not, like some of the other Cape species, 
select those to the exclusion of dry and grassy plains. 
Although I am not possessed of the information which would enable me to state positively 
the ao'e at which Circus Swainsonii attains its mature plumage, yet I have reason to believe it 
appears with the moult of the second year. A female of the first year is represented in Plate 
XLIV ; and fig. 2 of Plate XLIII is a male probably in its second year, just before the adult 
garb had been fully acquired. The plumage of the young differs not only in colour, but in 
various other respects from that of the adult. The feathers in the former, besides being more 
numerous, better formed, and of a more compact texture, are shorter, broader, and more 
pointed than in the latter. 
This is not the only bird of prey, in which we have observed the texture and form of the 
feathers to vary with age. In many of the Accipitres of South Africa, like changes occur ; and 
we find those who have the feathers long, narrow, and pointed in youth, have them short, and 
with rounded or semicircular points, in mature age — and vice versa, though not in the same re- 
markable degree. Thus diagnostic characters, drawn from the configuration of feathers, will 
not prove universally applicable ; indeed, in several instances in which attempts have been 
made to render the form of these available in the determination of species, confusion and error 
have been the result. The long and pointed feathers of Le Chass-jiente, Levaillant, have been 
advanced by some authors as the best and readiest characters, by which it was to be distin- 
guished from Vultur fulvus, Lin., of which it is only the young. Having examined hundreds 
of specimens of the vulture in question, I invariably found all individuals with sallow-coloured 
plumage — a mark of youth— to have the feathers narrow and pointed, even in the collaret ; 
while in those with a pale-coloured plumage — one of the indications of maturity they weie 
broad and semicircular at the points ; while the collaret consisted of coarse, wiry, or decom- 
posed feathers, which, in appearance, almost resembled a ruff’ of slender bristles. I often met 
with specimens, also, in the intermediate stages between these extremes ; and in many I ob- 
served feathers of both descriptions upon the same individuals. In the three vultures which 
occur in South Africa {V. fulvus, Lin., V. auricular is, Daud., and V. occipitalis, Burchell,) 
one law seems to prevail ; the feathers, in the young of all, are long, narrow, and pointed in 
the adults, they are short, broad, and rounded, or semicircular at the points. 
Facts such as these, testify what caution is required, in order to estimate correctly the value 
of characters, as they appear in individual specimens, which may be presented for examination. 
Nothino' short of a total revision of the characters, both of groups and species, will tend in the 
slightest degree to free our science from the anomalies, perplexities, and contradictions 
by’which it is at present swallowed up. Such an inquiry, if cautiously and patiently carried 
through, would supply either what is required, or prove that such a regularity as would enable 
the naturalist to detect fixed and general laws, does not exist in nature ; or at least is not to 
be discovered by the cultivators of Natural History of the present day. If the revision 
be attempted, the degrees of development of individual parts or organs ought especially 
to be minutely examined, with a view to discover how far such may be available to classifica- 
tion At present, we find the degree of development of some one external organ, often consi- 
dered sufficient to constitute a distinct species, though all other characters of the specimen 
may be strictly in keeping with those of a species, long known to science. My experience, 
