J 
nomenon as hatred; they are either manifestations of fear, a much sim¬ 
pler form of mental activity, or are alarm-cries, uttered for the purpose of 
calling others to the rescue ; that is, they are dependent on a rudimentary 
reasoning faculty, which is but a slight advance on instinct and grows out 
of it. That a fixed animosity does not exist in birds is plainly shown by 
the fact that species hostile to small birds during the breeding season on¬ 
ly, such as Crows and Jays, dwell with them in comparative peace during 
the rest of the year, however great the aversion manifested while the 
eggs and young are in the nest. Raptorial birds are of course always re¬ 
garded as natural enemies, but, judging from the analogy of the former 
case, it seems probable that they are only held in fear which has grown 
instinctive. 
From the facts above given, and from many others of a like nature that 
might easily pe presented, it seems hardly reasonable to suppose that the 
songs of birds have any more psychical significance than many other phe¬ 
nomena which they manifest. As before indicated it is easy to imagine 
that the endless variety of notes which they produce might be, judged by 
a human standard, expressive of an indefinite number of moods of mind. 
It seems, however, to be a general law among vertebrates, excluding man, 
that the vocal powers are developed, not according to the position occu¬ 
pied in the whole series, but according to the mean degree of physical ac¬ 
tivity attained. Though there are exceptions to this, they are not sufli- 
ciently numerous to destroy its force as a law. Birds are by far the most 
active of all vertebrates. Metabolism and catabolism reach in them their 
climax, the bodily temperature is higher than in any other class.; the vital 
functions are performed with greater rapidity, and hence the vocal pow¬ 
ers reach a higher stage of development. The same law holds within the 
class as in the whole vertebrate division. For example, the Vultures and 
Herons, which are comparatively sluggish, have very limited voice powers 
or none, while the Sparrow and Finch family, which are among the most 
active of birds, are unsurpassed in the gift of song. 
The subject will doubtless admit of infinite research, and presents op¬ 
portunities for many interesting discoveries. I have here presented, but 
in a very brief and general way what seems to me the, most natural, an^ 
iu fact the only reasonable theory regarding it. 
