6 UNIVERSITY OF COLORADO. 



beginning of life upon earth species have been engaged in a constant struggle 

 for existence. In the effort to perpetuate itself, each species is more 

 prolific than would be necessary were there no enemies. So any species in 

 time would populate the whole earth were it not kept in check by its enemies, 

 and having covered the earth, would become so abundant that there would 

 not be food enough for all, hence it would check itself. 



Darwin considered this subject in his Origin of Species, especially in the 

 chapter on the "Struggle for Existence." Among many other examples he 

 says the bumble-bee is one of the few, if not the only, insect capable of 

 visiting and pollenizing the red clover ; that the number of the bees in any 

 region depends largely upon the number of field mice, as the latter destroy 

 the combs and nests of the bees ; that the number of mice depends largely upon 

 the number of cats (he might better have said hawks and owls), because the 

 cats destroy many mice. 



Hence it is quite credible that the presence of a feline animal in large numbers 

 in a district might determine, through the intervention first of mice and then ol bees, 

 the frequency o certain flowers in that district. 



Fisher (1) tells of a marsh in New York inhabited by ducks, snapping 

 turtles and other animals. The turtles laid their eggs in the sand, and skunks 

 ate many of the eggs, thus preventing the overabundance of turtles. When 

 skunk fur became valuable, those animals were killed for their fur. Then 

 the turtles multiplied so that their ordinary food was not sufficient, and 

 they began to prey upon the young ducks. Thereupon the ducks de- 

 serted the marsh as a nesting place. Finally skunk fur became less valu- 

 able and the boys began to catch turtles for the market, thus restoring the 

 equilibrium, and the ducks in time returned to the marsh. 



According to Dr. Smith, of the United States Bureau of Fisheries, an 

 alarming scarcity of lobsters on the Breton coast was recently attributed 

 to a scarcity of eels, which usually keep in check the octopus, an active 

 enemy of the lobster (2). 



Herons in the South eat many crayfish. Crayfish are said to feed 

 upon fish spawn. Young fish eat mosquito larvae (3). As the mosquitoes 

 are the hosts of the malaria germ, it is quite conceivable that the destruc- 

 tion of the herons might have a disastrous effect upon the health of the 

 human inhabitants. 



These and numerous other instances of similar nature illustrate the 

 danger of unnecessarily disturbing Nature's delicate adjustment, the im- 

 portance of which is not generally realized. The evolution of species has 

 been in progress for ages, and during all those ages all species have been 

 adjusting themselves to their environment. Birds were already well de- 

 veloped far back in geologic time. The Jurassic Archaeopteryx was fully 

 feathered and winged. Hence the preservation of birds is necessary not 

 merely because some species are insectivorous, others engaged in warfare 

 against pernicious rodents, others devoted to the destruction of weed seeds; 

 but also because their unnecessary destruction means a reckless disregard 



(1) Fisher, A. K., The Economic Value of Predaceous Birds and Mammals, 

 U. S. Dent. Agric.. Yearbook for 1908, pp. 191-192. 1909. 



(2) Nat. Geog. Mag., Vol. XX, p. 553, 1909. 



(3) Baynard, Oscar E., Food of Herons and Ibises, Wilson Bulletin, Vol. XXIV, 

 pp. 167-169, 1912. 



