BIRDS OF PORTO RICO. 15 



fri'givorous or develop an abnormal appetite for the abundant 

 lizards and tree toads, which already suffer enough from the depre- 

 dations of native forms of bird life and under the added weight of 

 new enemies might be exterminated. 



It is very doubtful if birds of well-known habits introduced from 

 the United States would breed and rear their young under tropical 

 conditions. Only an occasional species seems able to sustain itself 

 when subjected to a new environment, and in order to do so it must 

 be capable of assimilating a somewhat omnivorous diet, as forms 

 specialized in regard to food or habits are almost certain to perish. 



Should it be desired, however, to experiment in the introduction 

 of extralimital birds, the barn owl (Tyto perlata) is recommended, 

 as this bird is almost cosmopolitan in its range. Raptorial species 

 are rare on the island, and as the fondness of the barn owl for rats 

 is well known it is likely to prove a profitable introduction. In case 

 the attempt is made, birds should be secured from Cuba or Jamaica 

 or from as far south in the United States as possible, and shelters 

 in the form of dove cotes should be provided for them in secluded 

 places bordering the cane fields. It would be necessary to supply 

 them with a small quantity of food until they become accustomed to 

 the change of environment and could become self-supporting. 



Should the birds increase, other shelters would have to be pro- 

 vided, as natural cavities are not found in sufficient numbers. 



At present no species capable of coping with the changa or caculo 

 can be suggested which would thrive on the island and not be de- 

 structive to other interests. In clearing any circumscribed terri- 

 tory of its original forest and introducing methods of agriculture 

 more or less intensive, great changes are wrought in the relations 

 of the manifold interdependent forms of life found therein. This 

 is shown plainly in the bird life of the island of Porto Rico. Cer- 

 tain species entirely dependent upon forest conditions for a suitable 

 habitat have become very rare or in some cases extinct. Others 

 more plastic, changing their haunts in conforming with new con- 

 ditions, have held their own, or, in a few cases, have increased in 

 number. It can not be supposed that in pre-Columbian times, when 

 the island was entirely covered with trees, such birds of the open as 

 the blackbird, ani, and gray kingbird were found in anything like 

 their present numbers. Happily, the disappearing species are not 

 highly beneficial and their place is filled by individuals of much 

 greater economic value. To introduce a number of foreign species 

 when nature is striving to attain equilibrium would only cause fur- 

 ther disruption and disturbance. Energies should rather be directed 

 toward the increase in number of the native birds, whose habits are 

 better known and understood. 



