WHY DO ANIMALS BECOME EXTINCT? 231 
such havoc with the blue-birds, while in the 
vicinity of Washington, D. C., the fish-crows 
died by hundreds, if not by thousands. 
Fishes may also be exterminated over large 
areas by outbursts of poisonous gases from 
submarine volcanoes, or more rarely by some 
vast lava flood pouring into the sea and actually 
cooking all living beings in the vicinity. And 
in the past these outbreaks took place on a 
much larger scale than now, and_ naturally 
wrought more widespread destruction. 
A recent instance of local extermination is 
the total destruction of a humming-bird, Bel- 
lona ornata, peculiar to the island of St. Vin- 
cent, by the West Indian hurricane of 1898, 
but this is naturally extirpation on avery small 
scale. 
Still, the problems of nature are so involved 
that while local destruction is ordinarily of 
little importance, or temporary in its effects, it 
may lead to the annihilation of a species by 
breaking a race of animals into isolated groups, 
thereby leading to inbreeding and slow decline. 
The European bison, now confined to a part of 
Lithuania and a portion of the Caucasus, seems 
