SCIENCE-GOSSIP. 



269 



INSTINCT. 



By R. Dickson-Bryson, 

 (Continued ft 



Instinct of Construction. 

 HPHE true beaver is now rarely found except 

 among the solitudes of the far North of 

 America. It formerly ranged from the Mexican 

 Gulf to the Arctic shores, and from the Pacific to 

 the Atlantic Oceans. The merciless pursuit of 

 beavers has almost exterminated them. There is 

 only one species of the true beaver, unless the 

 European beaver is a differen t 

 animal. This question has 

 been long debated among 

 naturalists ; but their differ- 

 ence of habits and anatomi- 

 cal structure would appear 

 to justify the distinction. 

 The European beaver is 

 very rare, and is usually 

 found by the Rhone. Un- 

 like its American congener, 

 it burrows on the banks of 

 the River Rhone, does not 

 construct dams, and lives in 

 isolated pairs. 



The true, or Canadian, 

 beaver (Castor fiber) is a 

 rodent, that is a mammal, 

 with large, slightly curved, 

 incisive teeth, which, owing 

 to a peculiar arrangement of 

 the jaws, act like scissors or 

 a carpenter's chisel. It is 

 distinguished from the other 

 animals of its order by its 

 broad, fiat, oval-shaped scaly 

 tail and webbed hind feet. 

 The beaver lives in isolation 

 part of the year and only 

 emerges from his winter 



home towards the end of May. At this season 

 they associate to the number of three or four 

 hundred to form a colony. This dual mode of 

 life is a necessity of their existence. During the 

 long and severe winters of their native haunts 

 they would be victims of a rigorous famine if their 

 intuitive sagacity did not lead them to lay up a 

 sufficient supply of food. Hence the conjunction 

 of their labours during the summer. They must 

 procure food, and from its nature it must be pre- 

 served by special means. Houses fitted for this 

 purpose must be built and dams constructed. 

 Their food consists of roots, fresh bark and tender 

 branches, and to be kept suitably fresh must 

 be preserved in water, and steps be taken to 

 prevent the water freezing. If the beavers are 



B.A., F.P.S., F.R.As.S. 



om page 237J 

 established on the banks of a river the water must 

 be maintained at a constant level, and the depth 

 be such that the surface layers only will freeze. 

 If, however, their quarters are near a lake they 

 confine themselves to building huts. The surface 

 of the lake is usually uniformly level, and there is 

 therefore no necessity for a dam. 



Having selected a suitable place, they at once begin 

 to construct a dam. The 

 materials used are driftwood, 

 green willows, birches and 

 poplars, also mud and stones. 

 They proceed some distance 

 up the river and select those 

 trees which, when felled, 

 will fall into the river and 

 be floated to their destina- 

 tions. They begin to gnaw 

 the trunk some distance — 

 generally three or four feet 

 from the ground, and on the 

 side facing the stream, so 

 that it may fall into it. Here 

 are two very important facts 

 displaying extraordinary in- 

 genuity : the utilization of 

 the stream for transport, 

 and the mode of felling the 

 tree. It is difficult to ascribe 

 them to mere instinct, being 

 the acts of a rational being. 

 When the tree is felled they 

 strip it of its branches, and 

 of these they make staves or 

 piles. One beaver holds the 

 pile in a vertical position, 

 while others scrape away 

 the earth, forming a cavity 

 into which it is inserted, then they replace the earth 

 to keep it in position. They subsequently fix these 

 piles by intertwining them with long and flexible 

 branches. They complete the edifice by covering 

 the whole with mud and stones, thus giving to it 

 the needful solidity. If the current is very strong 

 the dam is curved and the convex surface is turned 

 towards it. The base, also, is broader than the 

 summit, so that instead of a vertical wall it is 

 sloped. The whole arrangement is calculated to 

 resist great pressure. 



It is difficult to admit that there is no higher 

 power in operation than instinct. The beaver, 

 without instruction and scientific knowledge, the 

 acquisition of which costs us so much, is at once 

 a skilful builder and engineer. It constructs dams 



Beaver-huts and Beavers. 



