614 



NATURALIST'S GUIDE TO THE AMERICAS 



than 200 in., which renders this area one 

 of the wettest in America. 



Clearings are few, and aside from the 

 rather extensive, open, grassy savannas 

 near the Pacific coast, and smaller grass 

 areas in the Chagres Valley, the Isth- 

 mus is a practically unbroken expanse 

 of forest. 



Under the stimulating influence of 

 frequently recurring showers and con- 

 tinuously moist conditions throughout 

 the j^ear, the Atlantic watershed main- 

 tains a much more exuberant growth of 

 vegetation than the Pacific watershed, 

 where long periods of drought check 

 vegetative vigor. At the height of the 

 dry season the trees of the Atlantic 

 forest are clothed with brilliant ever- 

 green foliage, while those of the Pacific 

 forest, truly deciduous for the most 

 part, present bare stems, and the land- 

 scape has an autumnal appearance, 

 relieved to some extent along the 

 streams. 



C. Natural life areas 



Three principal life zones are recogniz- 

 able in the republic, extending at low 

 elevations from sea to sea, and at higher 

 elevations as belts on the slopes, or 

 embracing the tops of mountain ranges. 

 Beginning at sea level these are the 

 Lower Tropical Zone, of which there 

 are well-marked arid and humid divi- 

 sions ; the Upper Tropical or Subtropical 

 Zone, and the Temperate Zone. As 

 elsewhere the major life zones are 

 obviously subdivisible into minor re- 

 gional faunas and floras, or plant and 

 animal associations of varying rank, 

 most of which are very imperfectly 

 known. A few only of the more char- 

 acteristic mammals, birds, and plants 

 are mentioned as indicators, and the 

 zonal position of some of these may be 

 subject to revision, when their distri- 

 bution areas have more completely been 

 delimited. 



1. Lower Tropical Zone. An area of 

 high temperature including by far the 

 greater part of the Isthmian land surface 

 from the Atlantic and Pacific shore lines 

 across at low elevations from sea to sea 



and to about 3000 to 3500 ft. in average 

 altitude along the slopes of the higher 

 mountains. Many species of animals 

 and plants range in suitable places 

 throughout the zone; others are re- 

 stricted to the arid or humid divisions, 

 or reach their greatest development 

 there. 



a. Humid Lower Tropical Zone (Low- 

 land rain forest). The Humid Lower 

 Tropical Zone occupies the crests of 

 most of the mountain ranges, and nearly 

 all that part of the Atlantic watershed 

 of Panama lying below about 3000 ft. 

 altitude. It is replaced, however, by 

 a strij) of Arid Lower Tropical Zone 

 which extends from the Pacific coast 

 across the continental divide in the 

 vicinity of the Panama Canal, but the 

 transition to humid conditions is rapid 

 to the northward of Empire and the 

 bend of the Chagres River. The area 

 is comparatively uniform in character, 

 usually heavily forested, and includes 

 the most luxuriant vegetation on the 

 Isthmus. 



Mammals: Marmosa mexicana isth- 

 mica (Isthmian marmosa), Marmosa 

 invicta (Black marmosa). Philander 

 laniger derbianus (Derby's opossum), 

 Peramys melanops (Panama peramys), 

 Mazama sartorii reperticea (Canal Zone 

 forest deer), Tapirella bairdii (Baird's 

 tapir), Neacomys pictus (painted bristly 

 mouse), Oryzomys bombycinus bombyci- 

 nus (silky rice rat), Oryzomys caliginosus 

 idoneus (Panama dusky rice rat), Necto- 

 mys alfari efficax (Cana rice rat), Hete- 

 romys australis conscius (Cana pocket 

 mouse), Heteromys desmarestianus zona- 

 lis (Canal Zone pocket mouse), Dasy- 

 procta punctata isthmica (Isthmian 

 agouti), Microsciurus alfari venustulus 

 (Canal Zone pygmy squirrel), Bassari- 

 cyon gabbii gabbii (Costa Rican bushy- 

 tailed olingo), Sylvilagus gabbi gabbi 

 (Gabb's rabbit). 



Birds : Leucopternis ghiesbrechti 

 (Ghiesbrecht's hawk), Odontophorus 

 marmoratus (marbled partridge), Eury- 

 pyga major (sun bittern), Leptotila 

 cassini cassi7n (Cassin's dove), Neomor- 

 phus salvini (Salvin's ground cuckoo), 



