FOREST COMMUNITIES 423 



they frequent its borders. The sense of sight is said to be less developed 

 in the African forest-inhabiting okapi than in the antelopes of the 

 grasslands, 4 and the same is true for other mammals of the dense 

 primeval forest with the exception of the apes; elephants, for example, 

 and all species of swine permit close approach. In contrast, the sense 

 of hearing is the most important one in the forest. It serves as a means 

 of holding together monkey bands and flocks of birds which call con- 

 tinually in their course through the woods. Birds and mammals of the 

 forest are much more noisy, in general, than those of the grassy plain. 



Terrestrial mammals in the forest. — The non-arboreal mammals 

 of the forest include, besides the larger forms to be enumerated below, 

 a series of small creatures. These are frequently inhabitants of the 

 humus stratum, where they are protected even from the rigors of winter 

 in the northern forests (cf. p. 422). In temperate forests the long- 

 tailed and short-tailed shrews, Sorex and Blarina, are confined to this 

 forest floor and barely subterranean stratum, and with them are found 

 various rodents such as the pine mouse, Pitymys, red-backed mouse, 

 Evotomys, the lemming mice, Synaptomys, and the partly arboreal 

 ubiquitous white-footed mice, of the genus Peromyscus. Certain moles 

 may inhabit the forest, like the star-nosed mole of northeastern North 

 America. In the tropics numerous small rodents inhabit the forest 

 floor; and shrews of the genus Crocidura, in Africa and in the Orient, 

 replace the familiar Blarina and Sorex. 



An important selective factor in the forest habitat lies in the fact 

 that fast locomotion is prevented. The larger mammals are especially 

 impeded. Of large mammals, only the elephant, buffalo, okapi, river 

 hog, and leopard occur in the African rain-forest; all the remaining 

 hosts of large African mammals are limited to the open country. Move- 

 ment in the dense forest requires certain adaptations; strength and 

 weight of body, short limbs, and a wedge-shaped head are effective in 

 moving through undergrowth. Antlers and horns are little developed 

 among forest mammals in the tropics. The small buffalo and the rare 

 forest antelopes of the Congo have strikingly small horns. The wood- 

 land caribou of North America bears smaller antlers than those of the 

 barren-ground caribou, which is a smaller variety. 5 Moose are an ex- 

 ception, but the suggestion is common that they have only recently 

 become forest dwellers. In general, the ungulates in the thick forest 

 are mostly small; species of Tragelaphagns, Nesotragus, and Cephal- 

 ophus live in the xeric tropical forest and are able to wind through 

 the dense underbrush; the forests of Chile shelter the dwarf deer, Pudu 

 humilis, which is only 34 cm. tall; the dwarf musk deer (Hyaemoschus) 



