232 ANIMALS OF THE PAST 
to be slowly but surely approaching extinction 
in spite of all efforts to preserve the race, and 
no reason can be assigned for this save that the 
small size of the herds has led to in-breeding 
and general decadence. 
In other ways, too, local calamity may be 
sweeping in its effects, and that is by the de- 
struction of animals that resort to one spot dur- 
ing the breeding season, like the fur-seals and 
some sea-birds, or pass the winter months in 
great flocks or herds, as do the ducks and elk. 
The supposed decimation of the Moas by severe 
winters has been already discussed, and the 
extermination of the great auk in European 
waters was indirectly due to natural causes. 
These birds bred on the small, almost inac- 
cessible island of Eldey, off the coast of Ice- 
land, and when, through volcanic disturbances, 
this islet sank into the sea, the few birds were 
forced to other quarters, and as these were, un- 
fortunately, easily reached, the birds were slain 
to the last one. 
From the great local abundance of their re- 
mains, it has been thought that the curious 
short-legged Pliocene rhinoceros, A phelops fos- 
