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it is withdrawn and passed to another, and often to a third, until a 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