638 REPORT OF THE HARVARD AFRICAN EXPEDITION 
Department of Birds, Museum of Comparative Zoology, and to Dr. Herbert 
Friedmann, Curator of Birds, U. 8. National Museum, who has made a 
special study of African birds; nor can I let the opportunity pass without 
acknowledging the enthusiastic help in collecting and preparing specimens in 
the field rendered by my associates in the Expedition, particularly by Mr. 
Loring Whitman, Dr. Joseph Bequaert, and Dr. David H. Linder. 
EcoLoGy 
In its primeval state Liberia was no doubt very largely covered with high 
forest favored by the heavy rainfall and tropical heat, for this corner of Africa 
is said to have the greatest annual rainfall of any part of the continent with 
the possible exception of Sierra Leone or the northern Cameroons. According 
to Sir Harry Johnston, the annual precipitation for the coast region near Mon- 
rovia may exceed 150 inches, and probably diminishes slightly as one goes 
inland toward the Mandingo country in the northeast portion of Liberia, where 
the land rises somewhat. His map (1906, vol. 2, p. 523) outlines the forest 
region as extending in a narrow belt from the Gulf of Guinea to the southern 
border of Gambia, as a thin prolongation of the Congo Basin forest. At its 
widest part it is represented as including the entire width of Liberia but un- 
doubtedly it is less heavy and extensive eastward of that country as the rainfall 
diminishes and the forests give place to scattered tree growth and grassy plains 
in French Guinea. There is no doubt that human agency is responsible for a 
considerable modification of the Liberian area through the gradual clearing 
of the forests by the natives and the preparation of this cleared land for rice 
crops over a long period of time. Especially in the eastern part of the country 
and locally here and there along the more travelled routes leading back into 
the interior, these clearings are very extensive, but usually the original con- 
dition of the country may be guessed by the fact that here and there between 
cleared areas or along the tops of ridges remnants of the original giant trees 
still stand, or more extensive patches of virgin forest remain with nothing 
but clearings and occasional areas of low scrubby second growth for long dis- 
tances between. Probably, as elsewhere in the forest area of Africa, the once 
transcontinental forest has gradually dwindled, due in part to lessened at- 
mospheric moisture to the eastward, in part perhaps to slight changes of level, 
forming barriers that withdraw a certain amount of this water, and again, 
perhaps, due chiefly to human agency in cutting down the virgin forest, thereby 
drying out small areas which do not recover for many centuries, if at all. 
Originally Liberia probably offered two chief types of habitat, each with its 
characteristic fauna and flora, namely, the forest, with its several stories of 
higher and lower trees and the thickets of vines and bushes underneath, es- 
pecially along the edges of openings; and second, the waterways or permanent 
streams which transect the land from east to west or nearly so at frequent 
intervals. The effect of human agency has been chiefly to modify the forest 
environment, by causing openings into which come various species characteris- 
tic of open ground or of the low thickets and edges of the copses which presently 
