May, 1916 
A VISIT TO HAT AND EGG ISLANDS 
117 
southwest side of the island, where the birds were the most abundant and the 
view less obstructed by rocks and vegetation. By actual count of the birds 
in figure 36, there were found to be 391 on the wing above the sky line and 330 
below. Allowing a ten percent increase in the latter to account for the birds 
that are concealed behind the rocks and vegetation, there would be a total of 
754 birds that were within the field of the camera. Taking as a very con- 
servative estimate that this picture would include one-tenth of all the gulls 
that inhabit this island, we get 7540, or practically eight thousand as an esti- 
mate of the gull population. Other estimates, however, range from 15,000 
to 20,000. 
There were, perhaps, two thousand White Pelicans, some four hundred 
Great Blue Herons, and about fifty Caspian Terns. Thus summarizing, we 
would get the following as an approximate estimation of the bird population 
of Hat Island. Considering the small size of the island, it will be seen that its 
population is relatively dense. 
Fig. 37. Nesting Gulls. Practically all the birds are facing the sun. 
California and Ring-billed Gulls 8,000 
White Pelicans 2,000 
Great Blue Herons 400 
Caspian Terns 50 
Total 10,450 
Caspian Tern.— There were very few of the beautiful Caspian Terns; 
twenty-five pairs would probably include all that our party saw on the island. 
There was a small colony of about twenty that nested on the beach near the 
point where we had inadvertently pitched our camp. Some of the eggs 
examined in the colony were fresh, and others partly incubated. All the nests 
were located in a space not more than twenty feet square. The nests were 
built each in a small hollow about two inches deep by six inches in diameter, 
and were crudely lined with short sticks. The eggs in all cases were two in 
number. The outline of the egg showed a very pointed oval. They normally 
have a pale blue background and are mottled with a brownish pigment. The 
mottles or blotches are larger and more vivid on the large end of the egg. 
