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 



