doz ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
appearance during the dry season. This striking difference in the 
vegetation of the two divisions of the lower Tropical Zone is closely 
correlated with a corresponding difference in the animal life. On 
Barro Colorado Island we find the rain forest supporting a flora 
and fauna characteristic of the humid division of the lower Tropi- 
cal Zone, and the immediately contiguous area supplies haunts for 
aquatic species and others which are characteristic of clearings and 
cultivated lands. 
In this paper it is impracticable to go into the details of the life 
zone or even the chief biological features of the island, but I will 
restrict myself to an account of my work, some experiences with 
the birds studied, and some of the mammals met during the course 
of my summer in the Canal Zone. The reader is referred to the 
titles listed at the end of this paper for other aspects of the biology 
of Barro Colorado Island. 
In much of my work Mr. Josselyn Van Tyne, a recent graduate of 
Harvard University and now a graduate student at the University 
of Michigan, was associated with me. Mr. Van Tyne is a thorough 
and enthusiastic student of ornithology and his genial companion- 
ship is one of my pleasant memories of the summer. Many phases 
of our work, especially those which demanded constant uninterrupted 
observation, would have been impossible without the cooperation 
of a fellow worker. Mr. Van Tyne and I did not go to the station 
with any intention of studying the bird life as a whole and we made 
no great effort to identify a large list of representative species. 
Our main objective was to study a few species more or less inten- 
sively. This kind of work is yet a new field in the Tropics, and it 
added no little zest to our work to know that we were photographing 
and learning the habits of certain species for the first time. Only 
such specimens as were needed for identification were taken and it 
is gratifying to know that the collecting of large serges of skins is 
strictly prohibited. In addition to our needs in identification we 
tried to make the most of the specimens secured. Each bird col- 
lected was carefully weighed, a series of about 20 measurements 
were taken, and the color determinations of the iris and parts of the 
bird which are subject to quick change after death were made before 
the bird was skinned. Weights and determinations of the food, 
external and internal parasites, and diseases were all given special 
attention. We found the equipment of the laboratory, which in- 
cludes a drying room, scales, microscopes, a complete supply of 
chemicals and glassware, and a well lighted and screened workroom, 
ideal for this kind of detailed work. Furthermore there is an ex- 
cellent dark room, ice for cooling developers, running water for 
washing negatives, all that could be desired for our work in 
photography. 
