CONSERVING WILDLIFE — JACKSON 249 



nesting sites with hole-nesting birds such as the crested flycatcher and 

 the bluebird. 



Natural environmental and ecological changes. — Most of the natural 

 environmental changes that adversely affected species so as to hasten 

 their extirpation probably were climatic. Some of the major climatic 

 changes resulted in the glacial periods, or at least were associated with 

 glaciers, the general effects of which on the flora and fauna are known 

 to most students of biology. Glaciers caused the breaking up of the 

 geographic range of species into discontinuous distribution areas, 

 sometimes so small as to endanger the existence of the species. 

 Changes of climate associated with glaciation so affected the remnant 

 population of many species as to be their death knell, and in the 

 late Pleistocene glacial deposits are found the remains of many of 

 these species, and even genera, which became extinct at that time. 

 Glacial lake transformation, from fresh- water lake to acid lake, to 

 sphagnum bog, and to spruce woodland, completely changed environ- 

 mental conditions, often to the elimination of some species. Other 

 ecological transformations changed the environment and with it the 

 wildlife population. Volcanic eruptions might well have caused com- 

 plete annihilation of local forms of wildlife, as for example the blow- 

 ing off of the top of Volcan Santa Maria, Guatemala, in 1903, and 

 the Mount Katmai, Alaska, eruption in 1912. The eruption of Mount 

 Pelee, Isle of Martinique, Lesser Antilles, in 1902, quite possibly ex- 

 terminated the Martinique solitaire, an interesting and unique song- 

 bird. 



Weather. — Weather conditions, aside from those changes per- 

 manently effected by change of climate, may have adverse effects on 

 wildlife. Severe windstorms may, by creating clearings in the forest, 

 actually improve local environment for some wildlife species, yet a 

 storm of the same intensity on a marsh or a sandy area may destroy 

 much of the wildlife. It is probable that the Cape Sable seaside spar- 

 row, found only on the salt marshes of southwestern Florida, was wiped 

 out of existence by the Florida hurricane of 1937. The devastating 

 effects of drought on wildlife are fresh in our minds from conditions 

 created by drought in waterfowl nesting areas of the Northwest less 

 than a decade ago. Cold or wet seasons, especially during a breeding 

 season, may often reduce populations, sometimes to the danger point. 



Struggle for existence. — The "struggle for existence" is an old evo- 

 lutionary term, more or less hackneyed; nevertheless, overspecializa- 

 tion may place a species at a disadvantage in competition with forms 

 less specialized and better able to meet competition and changed en- 

 vironment. Gigantism, a type of specialization, may of itself have 

 been a factor in the disappearance of many of the gigantic reptiles 

 and mammals of past ages. 



