INTRODUCTION. 9 



grain fields gave way to extensive orchards, which gradually crept 

 up the hillsides and into the canyons, other species of birds began 

 to utilize the new kinds of food and also the safe nesting sites 

 afforded by orchard trees. Species that previously attracted little 

 attention soon increased in numbers because of the increased food 

 supply, additional facilities for nesting, and the protection afforded 

 by man, who killed or drove away their natural enemies. As a result, 

 some of them suddenly became of great economic importance, owing 

 to their increased numbers and destructive habits. 



MIGRATION OF BIRDS. 



Owing to its extent and varied topography, California is rich in 

 birds, both in species and individuals. Here altitude and topog- 

 raphy, as well as latitude, govern climate. This fact leads to many 

 peculiarities in distribution and complicates the study of birds in 

 their economic and other relations. The movements of birds, too, are 

 more complex than in the eastern part of the United States. The 

 regular migration north in the spring and south in the fall, which is 

 the rule over the greater part of the country, is here supplemented, In 

 the case of many species, by a migration from the mountains, where 

 they breed, to the valleys, where they winter. Besides the regular 

 migrations, at times remarkable incursions of a single species take 

 place. Such was the flight of mountain tanagers (Piranga luclo- 

 ciciana) in the valleys in May, 1896. In several parts of California 

 these birds appeared in immense numbers in localities where pre- 

 viously they had been rarely observed. Their appearance coincided 

 nearly with the ripening of the cherry crop, to which in some places 

 they did much damage in spite of the fact that great numbers of 

 them were shot. 



CAUSES OF DEPREDATIONS BY BIRDS. 



The failure of customary food supply sometimes leads birds to 

 forage upon crops which they do not commonly eat. This may be 

 the explanation of the depredations of robins in the fall and winter 

 of 1900-1901, when thousands of these birds pillaged the olive 

 orchards in Santa Clara Valley, the region about Santa Barbara, and 

 other parts of California. In that }^ear it was as much as the olive 

 growers could do to save part of their crop. Since then no case of 

 excessive loss of olives has been reported, though occasionally some 

 damage has been done. 



The amount of damage inflicted by birds upon a crop often depends 

 upon the surroundings. In the case of orchards in the midst of a 

 treeless plain depredations are mostly confined to such birds as nest 

 in them, but they may be visited and damaged by others during 



