VOl 'l*U Vm ] Recent Literature. 123 



Mr. Carriker's division of Costa Rica into life-zones deserves careful 

 consideration. Three Primary Areas, Boreal, Sonoran and Tropical, 

 are recognized. These are divided into six Regions, and these again into 

 fourteen Zones or belts. Judging by this list it is certainly true, as the 

 author states, after referring to the life zones of North America, that: "In 

 Central America, however, we have a much more complicated state of 

 affairs than in North America," for "some zones or belts of the Tropical 

 occupy exactly the same ground as some of the Sonoran, so that it is only 

 by studying the affinities of the various species and determining whether 

 they are modified Tropical or Sonoran forms, that we are able to account 

 for their presence in certain regions and give a reasonable explanation of 

 the finding of two widely different types in apparently the same zone." 



The practicability of such an arrangement is open to doubt, particularly 

 as the determination of the origin of many species is by no means an easy 

 matter and we fear that the author's attempt to draw a line between 

 "Tropical" and "Sonoran" species has not been wholly successful. For 

 example, the correctness of ascribing a northern origin to such species as 

 Planesticus nigrescens, Myioborus torquatus, Pheucticus tibialis, Amauro- 

 spiza concolor, Phainoptila melanoxantha and several others is surely very 

 doubtful. 



A notable feature of the Costa Rica avifauna is the remarkable rarity 

 of many of the resident species. Some of these are not found outside of 

 Costa Rica and the adjoining parts of Panama, and their rarity is believed 

 to be actual, and not merely apparent as in the case of many very local 

 species or those of retiring habits or found in inaccessible places. The 

 author believes that these rare species "belong to a vanishing fauna, and 

 for reasons of high specialization, interbreeding, or inability to hold their 

 own in the ever present struggle for the survival of the fittest, are slowly 

 disappearing." With so large and varied a bird population concentrated 

 in so restricted an area it is natural that many species should be able to 

 exist only in small numbers, and thus be ever in danger of extermination. 

 This fate has doubtless already overtaken several species and may explain 

 the apparent absence of a number of forms that have been found both 

 north and south of Costa Rica, as, for example, Amaurolirmias, Rhopoterpe, 

 Pyrocephalus, Myrmeciza lawrencei, Gampsonyx, Ictinia, Ceryle inda and 

 Rhynchortyx. 



There are several interesting facts in regard to the Costa Rica avifauna 

 and some interesting comparisons that may be made, that have not been 

 brought out by the author and it may be worth the space to go over them 

 here. 



As stated above the total number of forms given is 753. From this 

 number the five Cocos Island species may be subtracted as being not truly 

 Costa Rican, leaving 748 species and subspecies. Deducting the latter, 

 of which there are about 33, we have 715 full species remaining. 



It is of interest to compare this total with the number of species known 

 from the region covered by the A. O. U. Check-List. From this vast area, 



