INSTINCTS AND HABITS IN CHICKS 



29 



desire to continue the study of the effect of association of younger 

 with older chicks, eggs were set with the intention of having 

 another brood eight days after Group C, so that the difference 

 between the ages should correspond exactly with the difference 

 in age between the chicks of Groups A and B. But the plan 

 was frustrated to this extent, that the chicks of Group C came 

 out of the eggs one day before the date on which they were 

 scheduled to arrive, and a sudden change of temperature so 

 chilled the second setting that only two healthy chicks arrived 

 to constitute Group D. It was decided to make the most of 

 the opportunity, however, and records were taken of the pecking 



Ooys t 2 



9 10 11 12 13 14 15 16 17 1& 19 20 21 22 23 24 25 



Figure 3 — 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 " perfect " 

 reactions in a daily series of twenty pecking reactions. Curve IV-C shows the 

 improvement in accuracy of pecking in Group C; Curve IV-D, the improve- 

 ment in Group D. 



of the nine chicks in one group and the two in the other. When 

 the members of Group D were beginning their eighth day, the 

 cages of the two groups were thrown together and the chicks 

 allowed to mingle. For three days, beginning with this day, 

 loo pecking reactions per day were recorded for each chick in 

 both groups; and, continuing for a week after this, 50 reactions 

 a day were taken. It was thought that by this means the influ- 

 ence, if any, of one group upon the other might be more easily 

 and accurately detected. The results are plotted in fig. 3, and 

 the curves matched for corresponding ages as before. The 

 chicks of Group C had a pecking efficiency of 17.1 at the begin- 

 ning of their seventeenth day w^hen those of Group D joined 



