358 BULLETIN OF THE BUREAU OF FISHERIES. 
It is clear, therefore, that within a few years the guano industry will be 
dependent upon the yearly production of the birds. The amount of this new 
production can not be stated accurately, but it is fairly estimated to be between 
20,000 and 30,000 tons. This amount, if divided as now between the export 
and the home trade, would be of comparatively little value to either. The 
estimated annual production is, indeed, less in number of tons than is actually 
required by Peru’s agricultural industries alone; but since the new guano has a 
much higher average nitrogen value than the guano that is now used, and on 
which the estimated annual demand is based, it is probable that the yearly 
formation would meet the present demands of home agriculture. Furthermore, 
it is believed that with the adoption of the correct method of working the islands, 
and with the most thorough protection of the birds, there would result a mate- 
rial increase in the production of guano, sufficient to keep pace for a consider- 
able time with the growing demand. It is even possible that there would be 
a surplus for exportation. 
THE GUANO-PRODUCING BIRDS. 
At least twenty-four species of birds frequent the islands, not including 
seven species observed at sea in proximity to the islands and coast. Twelve of 
these were observed nesting on the islands. From the commercial standpoint 
the chief birds are the cormorant, the pelican, and the gannet, the first and last 
imentioned being the most abundant birds on the coast. 
THE CORMORANT. 
The white-breast cormorant (Phalacrocorax bougainvillet Lesson), the para- 
mount guano-producing bird, occurs along practically the entire coast, nesting on 
the level ground or the more gentle slopes, and always in closely crowded rookeries 
(fig. 9 and 10, pl. xv1). This cormorant, the “ guanay,”’ occurs most abundantly 
in the south, at the Ballestas and Chincha islands. The nests are closely crowded 
over great areas, where it may readily be ascertained that they average about 
three to the square meter. At the close of the season there may be allowed at 
least four birds to a nest, counting the parents and one pair of young. The 
population of a flock, after the young are raised, may therefore be estimated by 
multiplying by twelve the number of square meters covered by the rookery. On 
the Ballestas and Chincha islands in June, 1907, rookeries of 4,600, 10,000 to 
12,000, and 60,000 square meters, respectively, were measured, and other smaller 
rookeries were observed. These flocks, then, must have contained 55,000, 
120,000, and 720,000 birds, respectively. At a later time the last-mentioned 
flock, on the South Chincha Island, was so much increased, chiefly through 
recruits from the other flocks, that a million birds could have been only an 
underestimate of its population. The photograph (fig. 9, pl. xvi) shows but a 
very small portion of this immense aggregation of birds. 
