INTRODUCTION. XVii 
from the effects peculiar to its insular habitat, retains 
a plumage of the same colors throughout the year. This 
provision of nature for the other species, may be 
to give an additional security to the birds when the 
whole country of their northern homes is covered by 
snow, and so assimilate them to the surrounding white- 
ness, that their presence can only be perceived with 
great difficulty or by merest chance. 
Many Grouse possess a peculiar structure, rarely found 
in any other species, in the air sac on the side of the 
neck which is capable of being inflated, and then resem- 
bles somewhat an orange attached to the neck. By ex- 
hausting the air, which can be accomplished at the will 
of the bird, a booming sound is produced that may be 
heard at a great distance. This performance usually 
takes place at the breeding season, and is one of the 
male’s allurements to secure the attention and probable 
fleeting attachment of the females. At all other seasons 
this sac shrivels up and is mostly concealed under the 
feathers. 
One species of another group—Shore Birds—possesses 
a similar sac, but differently disposed and of great extent, 
which is also exhibited to advantage during the breed- 
ing season. This is the Pectoral Sandpiper, a descrip- 
tion of whose performance on the tundras of the far 
north I have given in my work on the Limicole. 
North America has been most favored among the 
countries of the earth in the great variety and number 
of her gallinaceous birds, many of the species being 
equal to any found in other lands and some surpassing 
all others known, in size, magnificent appearance, and in 
their value, commercially and otherwise, to the human 
race. They are a precious heritage, to be guarded care- 
fully and used judiciously if we are wise and far-seeing, 
