BLACK RAIL 161 
base. The blue and red tints become very vivid in 
the love-season. Without being anywhere abundant, 
the Black Rail is found throughout the Plata region 
in every place where reeds and rushes grow. In the 
marshes along the Plata they are met with quite as 
frequently in winter as in summer; this fact sur- 
prised me greatly, since I know this species to be 
migratory, their unmistakable cries being heard 
overhead every night in spring and autumn, when 
they are performing their distant journeys. Probably 
all the birds frequenting the inland marshes on the 
south-western pampas migrate north in winter, and 
all those inhabiting the Plata marshes and the Atlantic 
sea-board, where there is abundant shelter and a 
higher temperature, remain all the year. On the 
Rio Negro of Patagonia I found the Black Rail a 
resident, but the winter of that district is singularly 
mild; moreover, the wide expanse of waterless 
country lying between the Rio Negro and the moist 
pampas region would make an annual migration 
from the former places difficult to such a feeble flier. 
Of this instinct we know at least that it is hereditary ; 
and it becomes hard to believe that from every one 
of the reed-beds distributed over the vast country 
inhabited by this species a little contingent of migrants 
is drawn away annually to winter elsewhere, leaving 
a larger number behind. Such a difference of habit 
cannot exist among individuals of a species in one 
locality ; but differences in the migratory as in other 
instincts, great as this, are found in races inhabiting 
isolated or widely separated districts. 
L II 
