Reproduction 99 
Fear—stark, blatant, naked—does not disclose itself until the 
young are near nest-leaving age. This is a wise provision of 
nature certainly for otherwise fear would drive them from the 
nest at the approach of an alarming object before the proper 
time. Indeed fear and nest-leaving seem to be co-operative. I 
have noted that a nestling, a few hours prior to nest-leaving, 
would sit quietly in the hand, but a short time later, with the 
first trial of the legs outside the nest, would, when captured, 
struggle violently and squeal piteously. Having found their legs 
they also find the desire to use them for escape. Disease, starva- 
tion, improper development all retard this psychical growth. 
Thus one entire set, improperly nourished, responded up to the 
ninth day. In many nests one or more nestlings would, because 
they were from a few hours to a day younger, show a greatly 
retarded physical and psychical development from two to three 
days behind their more fortunate brethren. This was a result of 
the method of feeding (to be taken up later), whereby an advan- 
tage in age would permit the older young to secure most of the 
food (see Plates XXIII to XXVIII, inclusive). 
Growth of the young.—Rather extensive data, collected in 
this field, have been reduced to tables and curves (Tables 18, 
TABLE 18 : 
Growth in grams of an April set of Prairie Horned Lark nestlings to nest 
leaving, Ithaca, N. Y., 1927. 
Nestling No. 1 2 3 : 
deed oS 3.4 3.0 3.0 hae 
Sete 4.1 3.8 3.6 2.6 
nk eS 5.0 5.0 3.7 (lost) 2,3 dam) 
Fae cai a, MOE ere a tan G1 7.2 
nei ete ee ee 8.7 8.3 
Apa 26. 9.9 10.4 
Fe aig Ri pee ne 11.2 9.0 (dead) 
Mme ge eT eee 13.2 
RMS 14.2 
BOR Oe Ci cs 16.3 
WN Tis 17.0 
og, PE ee 18.1 
Av. daily increase. 1.33 0.98 0.80 0.20 
