416 NIGHT SONGSTERS. 
being unnatural to their constitutions, and that 
food would be easily obtainable, that temperature 
is the immediate cause of their hybernation, and 
that they possess a high susceptibility of that 
exact heat determining their torpid condition. If 
there were an instinct implanted in them causing 
them to disappear for a season merely from the 
absence of proper or sufficient food, it would not 
be found that they abstained from food for several 
days after their revival, or that when kept from 
burying themselves till the beginning of the year, 
they immediately resorted to that act on the 
first occasion, though food were obtainable, thus 
one given me in February, 1837, on being put 
into the garden, directly thrust itself into the 
ash-heap, and subsequently found a convenient 
spot for the remainder of the hybernating period. 
Artificial heat keeps them from positive torpidity, 
but never induces them to feed, and fails to rouse 
them from a permanent sleeping state. My brother 
finds that his tortoise which weighed four pounds 
on its disappearance, lost in the five months six 
ounces. 
Night Songsters—There are a greater number of 
birds which sing by night than Ornithologists 
usually conceive, and in fact a complete list has 
never yet been drawn up, the entire number of facts 
having been gradually ascertained and by Natu- 
ralists whose localities are far apart and who have 
communicated their observations to the world with 
considerable intervals of time. Some of these 
nocturnal songsters perhaps pour forth their notes 
at that time by mere accident or whim, having 
been disturbed in their repose and excited to song 
bythe cheerful moonlight, by the pleasant warmth of 
the nights of midsummer, or on the contrary by the 
sharp piercing cold of a winter night, rendered in 
some measure cheering however by the stillness of 
