504 COMMISSION OF EEEOK. 



instinct. Wandering from home is a common expression or 

 result of disease mental or bodily in certain animals. Thus 

 wandering fits occur in the sturdy of sheep. 



The migrations of animals are also supposed to be guided 

 by unerring instinct. But in the lemming they lead to the 

 deaths of thousands of animals, of whole armies of emigrants, 

 under circumstances which cannot at present be satisfactorily 

 explained ; while the migrations of fish appear to be marked 

 by occasional loss of way, just as happens frequently in the 

 case of migratory birds. In the latter the errors connected 

 with migration include the dashing against lighthouse 

 lanterns and telegraph wires, and shock or death from the 

 concussion. Too early or mild springs in northern climates 

 attract migratory birds, only to die of the later frosts. 



The migratory instinct frequently leads to the commis- 

 sion of fatal errors as in the case of the smelt ' sculls ' (or 

 shoals) of which ascend the North-American rivers and 

 streams in such numbers and with such impetuosity as to 

 cause death by the thousand from overcrowding (Adams). 

 The salmon both of North America and Britain make many 

 equally fatal mistakes of a similar kind in their too eager 

 rush up shallow waters, for instance. In caged migratory 

 birds, at the epoch of the spring or autumn migration, on 

 the other hand, the non-gratification of an imperious instinct 

 often leads to self-destruction, by frantic efforts at escape, 

 and death by exhaustion or self-mutilation. 



Nest-building in birds is another of those operations that 

 are supposed to be uniform in each species, and determined 

 by an unvarying instinct. But the fact is that birds are con- 

 stantly making mistakes either as to the (1) material, (2) 

 site, or (8) mode of construction of their dwellings. Star- 

 lings, swallows, chimney swifts, and other birds that frequent 

 man's dwellings, often pay the penalty of nesting in chim- 

 neys in use, the object of the birds being apparently the 

 securing of warmth. Death by fire or suffocation is the 

 occasional result of the inflammable material of the nest 

 catching fire. But not only is there danger in such cases to 

 the poor animals themselves. Man himself may be seriously 

 incommoded, as happened to myself on one occasion, when, 



