RECONSIDERATIONS 377 



such as water carries when poured on gently sloping even ground. 

 Actual leadership is taken up moment by moment by different sheep, 

 each temporary guide when a few inches ahead becoming scared, pausing, 

 and letting his neighbours on either side precede and accept in their 

 turn the responsibility and peril. By this method of advance no 

 individual offers too prominent a mark, each feels himself able in a 

 fraction of time to plunge sidelong into the mass, to lose himself in 

 comfortable nonentity. If the sheep domesticated for hundreds of years 

 cannot forget this sense of impending danger, wild creatures dare not 

 for a moment cease to suspect the unknown. This dread it is, I think, 

 which keeps large companies of animals voluntarily confined, penned 

 close in limited areas for considerable periods. The absolute numbers 

 of a congested horde are unimportant. It is the relation of numbers 

 to environment that decides the genesis of the trek. The numbers of 

 the rabbit in the Wairarapa, and of the goldfinch in lower Hawke's Bay 

 before their advance began, must have been immensely greater than 

 those of the sparrow or of the blackbird or thrush in Auckland. In the 

 case of the rabbit and of the goldfinch there was room for the enlarge- 

 ment of the circle and a consequent postponement of the initiation of 

 the trek. On the other hand, where the locality of liberation was limited 

 in space or feeding-ground, as in the case of the sparrow, blackbird, and 

 thrush, the time during which the circle could spread normally without 

 striking barriers meteorological, physical, and geographical, was sooner 

 reached, the movement of migration more quickly precipitated. 



We have imagined a deep distrust and suspicion of the unknown 

 sufficing to hold together a congregation of aliens in a strange land 

 sufficing to retard migration until further expansion has been blocked, 

 this fear of what may lie beyond counteracting the disabilities of less 

 clean feeding-grounds, less ample breeding accommodation ; we have 

 imagined the congestion becoming intolerable until the uneasy horde at 

 length breaks forth. The begetting force of the actual moment of migra- 

 tion can be conjectured with a fair degree of likelihood ; hardly a hint 

 would be required. A premonition of that deep inherited kind we call 

 instinctive would have permeated the inert and uneasy mass that 

 movement was in the air; change of ground would have been long 

 anticipated; the horde would be in a state of unstable equilibrium 

 charged with an instinctive restlessness, expectant as duck after dusk 

 for the signal to rise. Equality, however, amongst the lower creatures 



