ACCLIMATISATION CENTRES AND MIGRATION ROUTES 327 



the connection of observed animals and roadways that it is because the 

 observer is more on the road than off it will not hold good at Tutira. 

 Life on a rough run is spent not on but off the road ; for every ten miles 

 ridden by the author on roads, a hundred has been ridden in the wilds. 

 If, therefore, migrants have been relatively more often and at earlier 

 dates seen about highways than elsewhere, it is because they have been 

 followed at first as lines of least resistance and clung to afterwards as 

 guides to further goals. 



Their importance, indeed, as a factor in the spread of aliens can 

 hardly be estimated, except by realisation of what is called the inert 

 mentality of animals, but which might, perhaps, be better termed their 

 prudent conservation of energy. It is a truism that sheep in a field will 

 avoid obstacles as man himself does ; thistle-groves, clumps of fern, logs, 

 soft ground, will all cause deviation ; in fact, as I have said before, a 

 straight sheep-track is no more discoverable than a straight path between 

 village and village. Advantage is taken of the smallest saving of toil, 

 even such as that entailed by the stepping over a fern frond fallen out 

 from a clump, or the avoidance of a prone spar a few inches high. One 

 particular instance out of thousands occurs to me : On certain low hills 

 on Tutira a foot-wide track had been roughly slashed through low fern. 

 Such a track it is comprehensible sheep in " working " a paddock might 

 discover and prefer, but that a year later, when fire had run over the 

 whole area, they should rediscover a line by that time indecipher- 

 able to human vision, shows how the smallest saving of exertion is 

 appreciated. 



If advantages in ease of progression of so infinitesimal a kind are 

 thus taken into account, it is not difficult to understand the allurements 

 of a road, an entrancing surface free of logs, free of tangled grass, free 

 of hummocks, an open way allowing full vent to that mental sloth which 

 is the lower creatures' bliss. From four centres of liberation and by 

 four lines of ingress the coastal route, the hill-top route, the river-bed 

 route, and the highway of man has the modern alien invasion of Tutira 

 been accomplished. 



