26 INCUBATION. MIGRATION. 



9. There are also birds that build their nests upon the ground, 

 and in order to guard against their being submerged by heavy 

 rains, elevate them on hillocks of earth : these nests are con- 

 structed with less care : we here find only an abundance of down, 

 sustained by flexible twigs, suitably interlaced; finally, some 

 birds are content to form an excavation in the earth or sand, in 

 which they deposite their eggs, which for the most part they 

 assiduously sit upon, but which they sometimes abandon during 

 the day to the heat of the sun ; nevertheless, in this latter case, 

 their solicitude induces them to cover their eggs with a light 

 layer of sand or other matter, either to hide them from animals 

 that seek them for food, or to protect them from the too great 

 intensity of the sun's rays. 



10. The constancy of birds in sitting on their eggs is admira- 

 ble : sometimes both parents divide this care between them ; at 

 other times the male only watches the nest and brings food to 

 the female, while she remains sitting on the eggs ; and in other 

 species again, the female alone is charged with the incubation. 

 Generally, the mother only leaves her nest for a few moments 

 when pressed by hunger, and then seemingly with regret ; 'and, 

 in most cases, after her young have appeared, she bestows upon 

 them, and for a long time after their birth, the most tender care 

 and attention. She covers them with her wings to protect them 

 from the cold, brings them choice food, which she often half 

 digests, and then disgorges into their throat, to render it better 

 suited to their tender stomach ; she guides their first steps, 

 teaches them to use their wings, and when threatened by danger, 

 displays as much courage as devotion in their protection. 



1 1. In this particular, it is very interesting to study the habits 

 of birds ; but this is not the most remarkable point in their his- 

 tory. The most singular phenomenon in the lives of birds, is 

 unquestionably the habit, which certain species have, of making, 

 at appointed periods of the year, long journeys, and changing 

 their climate according to the seasons, 



12. Birds that feed on insects, early leave temperate climates 

 to go towards the south, where they find in the winter a more 

 abundant supply of food ; other birds change their country to 

 seek a place more propitious for their young, and go sometimes 



9. Do birds always build their nests in elevated situations ? 



10. Does the male bird ever assist in the process of incubation ? In what 

 way ? Are the young birds able to feed themselves when they first escape 

 from the shell ? 



1 1. What is the most remarkable circumstance in the general history of 

 birds? 



12. What are the reasons which induce many birds-to migrate ? 



