294 Observations on the 
preservation of species, Thus, birds that 
congregate and that live in society have 
usually a regular watch stationed in some 
commanding situation, whose note of alarm 
is understood by the whole cominunity: of 
the truth of this observation, fieldfares and 
rooks furnish familiar and striking instances. 
The shrill call of the swallow, the harsh 
scream of the jay, the petulant cries of the 
various species of titmouse, and the plaintive 
wailing of the flycatcher, likewise intimate 
the approach of an enemy. The reiterated 
cackle of the domestic hen after she has laid, 
speedily announces the joyful event; her 
cluck indicates that she has become the mo- 
ther of a family; by a peculiar call she in- 
forms her brood whenever she discovers any 
thing suitable for food; and her shriek is a 
‘warning against impending danger. What 
is usually called the prating of poultry is 
expressive of satisfaction and complacency : 
‘but it is needless to multiply examples, or to 
insist further on the many useful purposes to 
to which a familiarity with the language of 
birds may be rendered subservient: it will 
‘suffice to remark, that this knowledge sup- 
plies the means of making fresh discoveries, 
of correcting numerous errors, and of re- 
moving many of those doubts and difficulties 
