r 



I' 



FIG. 27-7 East face of meridian termite n< 

 characteristic of these nests to be oriented 

 broad surfaces presented one to the risii 



of 28 cm, and a slug 20 cm. Birds and mammals, 

 however, are usually smaller than their relatives in 

 temperate regions. Birds also lay fewer eggs in a 

 clutch than they do in temperate regions, but this may 

 be due to the shorter days that tropical birds have for 

 feeding. 



Since there is little variation in the duration of 

 light per day throughout the year, photoperiodism 

 is largely absent. In desert regions, the gonads of 

 birds may remain inactive and reproduction in- 

 hibited for a succession of seasons during a prolonged 

 drought, but their sexual cycles respond quickly to 

 rainfall, and nesting may begin within a few days 

 after heavy precipitation (Serventy and Marshall 

 1957). In regions where wet and dry seasons are not 

 developed, bird species may breed throughout the 

 year, although individual birds, after breeding, need 

 a period of rest before they can breed again (Chapin 

 1932, Baker 1938, Miller 1955). In the evergreen 

 rain forest of Borneo, where precipitation is ex- 

 tremely high, the onset of breeding among mammals 

 appears correlated with the period of the year when 

 precipitation is minimum rather than maximum 

 (Wade 1958). 



There is no definite period of dormancy or migra- 

 tion. Movements are largely localized and in quest 

 of ripening fruit or other food supplies. Away from 

 the immediate vicinity of the equator and toward the 

 periphery of the rain forest, where wet and dry 

 seasons become important, the annual cycle of breed- 

 ing, migration, and other activities becomes more 

 pronounced and important (Baker et al. 1936, Davis 

 1945, Wagner and Stresemann 1950, Moreau 1950). 



In dense rain-forest on the equator, the daily 

 rhythm of animal activities is striking. Many natu- 

 ralists have commented on the great hush of the forest 



edge to the 

 rson). 



during the middle of the day. The forest appears 

 empty of both birds and mammals. Thei'e is an occa- 

 sional note of a bird, but birds do not have the varied 

 and conspicuous songs that they do in temperate re- 

 gions. They may be glimpsed in the tree-tops or 

 searched out in the undergrowth moving through the 

 forest in loosely formed groups, each group com- 

 posed of a few individuals each of several species. 

 These social groups occur at all seasons, although 

 nesting birds must withdraw temporarily from them 

 (Davis 1946). The cicada chorus is often loud and 

 persistent; with the onset of darkness, other orthop- 

 teran insects burst into song to which tree frogs, 

 night birds, monkeys, and others add their voices. 



Nectar feeding is well developed in some tropical 

 birds, and many flowers depend on birds for their 

 pollination. Hummingbirds are numerous in the 

 Western Hemisphere. Many insects are also nectar 

 and pollen feeding, and these species are largely 

 limited to the tropics. Fruits are an important food 

 for many birds and mammals. Fruit-eating bats are 

 confined to the tropics. Sloths and ant-eaters have 

 powerful claws and long stick-y tongues with which 

 they open and plunder the nests of ants. Army ants 

 moving in large numbers over the forest floor in their 

 search for prey often attract a large and varied group 

 of birds, but these birds are after the other insects 

 that the ants stir up rather than the ants themselves 

 (Johnson 1954). 



As in most other terrestrial biomes, animals occur 

 in the greatest variety and numbers in the forest 

 floor. Here they are much more numerous during the 

 wet than the dry season. In the Panama Canal Zone 

 during the wet season there are between 4000 and 

 10,000 animals per m-, representing 294 species. Of 

 this fauna, mites constitute 25 per cent, springtails 



348 Geographic distribution of communities 



