CHAP. 11.] 
BIRDS. 
2 n 
the time of the ornithologist Wilson ; and the rice-bird, or “ Bob- 
o’-link,” of the Americans, continually widens its range as rice 
and wheat are more extensively cultivated. This bird winters 
in Cuba and other West Indian Islands, and probably also in 
Mexico. In April it enters the Southern States and passes 
northward, till in June it reaches Canada and extends west to 
the Saskatchewan River in 54° north latitude. 
South Temperate America . — The migratory birds of this part 
of the world have been observed by Mr. Hudson at Buenos 
Ayres. As in Europe and North America, there are winter and 
summer visitors, from Patagonia and the tropics respectively. 
Species of Pyroccphalus, Milvulus, swallows, and a humming- 
bird, are among the most regular of the summer visitors. They 
are all insectivorous birds. From Patagonia species of Teem* 
optera, Cinclodes , and Cent rites, come in winter, with two gulls, 
two geese, and six snipes and plovers. Five species of swallows 
appear at Buenos Ayres in spring, some staying to breed, others 
passing on to more temperate regions farther south. As a rule 
the birds which come late and leave early are the most regular. 
Some are very irregular in their movements, the Molothrus bona- 
riensis, for example, sometimes leaves early in autumn, some- 
times remains all the winter. Some resident birds also move in 
winter to districts where they are never seen in summer. 
General Remarks on Migration . — The preceding summary of 
the main facts of migration (which might have been almost in- 
definitely extended, owing to the great mass of detailed infor- 
mation that exists on the subject) appears to accord with the 
view already suggested, that the “ instinct ” of migration has 
arisen from the habit of wandering in search of food common to 
all animals, but greatly exaggerated in the case of birds by their 
powers of flight and by the necessity for procuring a large 
amount of soft insect food for their unfledged young. Migra- 
tion in its simple form may be best studied in North America, 
where it takes place over a continuous land surface with a con- 
siderable change of climate from south to north. We have here 
(as probably in Europe and elsewhere) every grade of migration, 
from species which merely shift the northern and southern 
