Vol l909^ VI ] Palmer, Instinctive Stillness in Birds. 33 



density, thickness, position, etc., determining. As the developing 

 species or groups broadened out into different environments and 

 thus came into interrelation with varied and numerous factors and 

 enemies those best fitted to escape, however slight the difference, 

 became collectively the progenitors of the mimicking and non- 

 mimicking groups or species of later times. It would seem that the 

 fixation of protective color gradation characters in feathers must 

 have been an early one; in fact there is abundant good reason for 

 believing that bright colors and feather specialization are more 

 advanced conditions and of later development than the sober, 

 simpler tints and feather shapes of mimicking birds. As color, 

 or its absence, when the bird is in motion, is of little or no value in 

 affording protection, it seems evident that the habit of keeping still 

 in the presence of danger, real or fancied, must have been at a very 

 early period instinctive and necessary in the developing groups of 

 nonpredatory birds, an instinct antecedent to the specialization of 

 feathers and probably derived from the weak, unspecialized and 

 evidently reptilian-like ancestors. It may therefore be contended 

 that colors in birds were not determined suddenly but by slow 

 gradational stages as a result of increasing experience and forming 

 habits, character of the food and the slow unconscious fitting to the 

 environments. This instinctive habit of stillness seems to be an 

 absolutely necessary feature of the life of the young of practically 

 all ground birds, but often absent in the adults, as in gulls and terns. 

 A young tern, for instance, instinctively remains motionless on our 

 approach, and we may be sure that its ancestors have always done 

 so also, but if handled for a time, it forgets its simulative caution 

 and does not readapt itself unless released and allowed to escape. 

 Its mimetic instinct becomes to a large extent lost in an unnatural 

 condition of safety and captivity, because its life is spared, which 

 is also an unnatural act. 



Nestlings, when their hunger is appeased are quiet and crouching, 

 they instinctively and quickly learn and obey the warning notes of 

 their parents. They are easily aroused by the motion of the arriving 

 parent, and sometimes by that of an intruder, but hunger and its 

 probable alleviation is the cause. Unnecessary motion by the 

 nestling is possibly dangerous to it, it may attract unfortunate 

 attention, consequently we find that the parents are constantly 



