DEFENCE OF THE YOUNG 81 



Herrick ('05, p. 181), whose continued, systematic studies have 

 added so greatly to our knowledge of the life of the nest, was among 

 the first to discover that admirable adjustment of the young bird's 

 nervous system which prevents it from being overfed. He writes: 

 "The food is placed not simply in the mouth of the young bird but well 

 down the sensitive throat, and if the bird does not immediately respond, 

 it is withdrawn and passed to another, and often to a third, until a 

 throat is found which has the proper reaction time. If the gullet is 

 already full, the swallowing reflex is inhibited, and the bird must wait." 



Nest Sanitation. Second only in importance to the subject of food 

 is that of nest-sanitation. The young of altricial birds as unlike as 

 Hawks and Hummingbirds void their excreta far pver the edge of the 

 nest, but with probably all our Passerine birds, and with some others, 

 it is enclosed in a membranous sac, which is removed and, in some 

 cases, devoured by the parent. 



Defence of the Young. Just how birds defend their young from their 

 natural enemies we cannot always say, but before man as a possible 

 nest-robber, some species (e. g. Pelicans, Flamingoes, Cormorants, 

 Ibises, Spoonbills, Herons, and most Raptores) desert the nest without 

 protest; others (Gulls, Terns, some Raptores) protest loudly and dart at 

 the enemy, sometimes actually hitting him; the Passeres, with some 

 exceptions (e. g. Crows and Jays), utter loud alarm or call notes, 

 which more often betray their secret than conceal it, and the Thrasher 

 will occasionally strike the intruder; while many ground-nesting birds 

 (e. g. Ducks, Snipe, Grouse, Nighthawks, Doves) seek to draw atten- 

 tion from their nest or young, by feigning partial helplessness and 

 fluttering painfully before the marauder, always, however, keeping 

 just beyond his reach; a wonderful exhibition of parental devotion the 

 origin and development of which it is difficult to explain. 



Voice. Some suggestions for a study of the notes of young birds 

 are made in the chapter on the " Voice of Birds." Their instinctive 

 obedience to parental command is also mentioned. Observe, for ex- 

 ample, how young Gulls, Terns or Grouse squat and remain perfectly 

 motionless in response to a certain alarm note; and how, under the 

 same stimulus, a brood of young Ducks scatters. 



Certain birds have a feeding note which induces the young bird to 

 open its mouth in preparation for the coming morsel. On leaving the 

 nest some young birds (e. g. Baltimore Oriole, Yellow-headed Black- 

 bird) develop a food-call, which is lost when they have learned to care 

 for themselves. 



Nest Exercises. While in the nest, young birds devote much 

 attention to their newly grown feathers, preening them carefully and 

 repeatedly. The parasites which infest some birds, notably Phoebes, 

 while in the nest, also give the young bird much occupation. The fre- 

 quent stretching of the wing is a characteristic nest activity, and, 

 according to Scott, the grasping of the nest-lining with the toes is an 

 important nest exercise. 



