i'Yur in Birds. 



but I believe that by far the greater number of such strays are driven forth by fright, and 

 when this perilous step has once been taken it can seldom be retraced. The young of 

 such birds as the Wilson thrushes, whose nests are on or near the ground out of the 

 reach of storms, are often found in this predicament.' 



Many immature birds which I have watched at the nest show no precise powers of 

 discrimination in any direc- 

 tion. You will see them 

 respond as promptly to the 

 flutter of a leaf or the call- 

 note of any passing bird as 

 to their own mother's voice 

 but a more curious specta- 

 cle may be witnessed when 

 a fledgling of one of our 

 common species like, the 

 Baltimore Oriole climbs to 

 the top of its nest. All the 

 others immediately salute it 

 as if it were an old bird, 

 and with open mouths beg 

 vainly to be fed. If a young 

 bird within a day of taking 

 flight cannot distinguish 

 one of its brothers from its 

 mother, it can hardly be 

 expected to " know a hawk 

 from a handsaw," or an 

 enemy from a friend. 



After taking flight the 

 young of altricial birds are 

 fed by one or both parents 

 for a period of days or 

 weeks, and much is quickly 

 learned by imitation and in- 

 dividual experience. Their 

 ingrained sense of fear becomes in the course of time gradually specialized in certain 

 directions. Fear of man, guns, hawks, snakes, cats and the various agents of destruction 

 with which each species must contend in the course of its life, seems in every ca>e t 

 be acquired or learned ratln-r than inherited. 



On the hist day of June I found a Cowbird nearly full-fledged but either unable or 

 disinclined to fly. He occupied the nest of a warbler, apparently the species known as 



1 The huge pot-belly of the young altricial bird has a U-.L- <|uiu- apart from the function of digestion. It anchors 

 it to the nest, and as in the modern " Brownie" keeps it right side up. The pliant viscera conform to every move- 

 ment, and form a central supporting pillar long before the legs can sustain the weight of the body. (See young 

 CeJar-birds in Figs. 113-115.) 



Fig. 118. Brown Thrush startled while at nest : attitude of keen attention. 



