126. Observations on Periodical Birds. 
scattered through the writings of such va- 
rious authors, and are so blended with what 
is erroneous or merely conjectural, that it is. 
no easy task to distinguish and collect them: 
consequently our knowledge of the circum- 
stances that regulate the motions of the nu- 
merous species of periodical birds, is. still 
very limited; and we are almost entirely 
ignorant of the places of their retreat, and 
of the mode of their existence in those re- 
treats. Whether, when they withdraw, they 
depart from those districts and countries in 
which they cease to appear, or whether they 
conceal themselves, and remain in a state of 
torpidity, has not yet been positively deter- 
mined; and opinions must continue to be 
divided on the subject, so long as authors 
indulge in fanciful speculations, instead of 
contenting themselves with collecting and 
arranging well authenticated facts, from 
which alone. legitimate conclusions can be’ 
deduced. 
The accumulation of facts, then, appears 
to be the most important object to be attained 
at present, and my principal motive for in- 
troducing the following tables and remarks 
to the notice of the Society, is the hope that 
they may be found to contribute, in some 
degree, to increase our scanty stock of in- 
