INSTINCTS AND HABITS IN CHICKS 



27 



the most critical stage of development, the curve on the whole 

 not only indicates that the co-ordination of movements that 

 constitute reaction 4 has a certain period of development, but 

 it roughly marks out that course. The rate of improvement is 

 not uniform from day to day, but is very much more rapid during 

 the first few days than later. 



Before discussing reactions i, 2, and 3 of this group, let us 

 be clear as to the meaning of these three reactions and their 

 relation to 4. In the first place, it should be noticed that the 

 records under i, 2, and 3 may be regarded as error records. 

 That is, under i are listed the errors of striking, under 2 the 



Triah 

 20 



18 



le 



14 



12 

 10 



8 

 6 



Days 1 



8 9 10 U 12 13 14 IS 16 17 18 



20 21 22 23 24 25 



Figure 2 — A comparison of curves of development of the pecking instinct to show 

 the possible effect of social influence. Distances along axis of abscissae repre- 

 sent days of age ; distances along axis of ordinates, the number of a given kind 

 of reaction in a daily series of twenty pecking reactions. Curve IV-A shows 

 the improvement in accuracy of reaction 4, Group A; Curve IV-B, the im- 

 provement in accuracy of the same reaction for Group B. Curve III-A shows 

 the course of reaction 3, Group A; Curve III-B, the course of reaction 3, 

 Group B. 



errors of seizing, and under 3 the errors of swallowing, if swal- 

 lowing here may designate the manipulation of the object after 

 it is seized. Although for convenience the term swallowing has 

 been applied to reaction 4, it is clear that reaction 4 is really 

 striking-plus-seizing-plus-swallowing in an errorless train. 



There are always three regular chances of error, then, at the 

 beginning of any pecking reaction. I shall aim to show the 

 rate of decrease of each kind of error separately, and, correla- 

 tively, the improvement in the co-ordination of the three 

 reactions. 



