BIRDS OF THE TRES MARIAS ISLANDS. 31 



Sula nebouxii Milne-Edwards. Blue footed Booby. 



Sitla pUcator Gmysoii, Proc. Boston Sue. N.at. Hist., XIV, p. 302, 1871; L:i.\vi., 



Mem. Boston Soc. Nat. Hist., II, i>. 316, 1874. 

 Siila nebouxii Milne-Edwards, Ann. Sci. Nat., Paris (Zool.), 6i'me sor., XIII, Art. 



4, p. 37, pi. 14, 1882 (Chile). 

 Sitlagossi Goss (ex Ridgway MS.), Ank, V, p. 241, July, 1888 (Gnlf of Calif.). 



Sida nebou.rii is the most abuudaut species of booby occurring on 

 Isabel and the Tres Marias. On April 22 they were breeding abun- 

 dantly on the beaches and on a low flat area that covers a i)art of the 

 former island. They were common on the grassy beach at the lauding 

 and thence back among the scrubby trees and bushes which form a 

 scanty growth over the flat. They were most numerous on the open 

 beach a little above high-water mark, but dozens of them were seen 

 with their eggs farther back among the bushes. Like the preceding 

 species, they fought and screamed savagely when approached. The 

 males usually flew away, but the females remained to give battle over 

 the nests, which were mere hollows in the earth, sand, or gravel. Not 

 a single young one was seen in the hundreds of nests on Isabel. 



The sun was excessively hot the morning of our arrival, and while 

 the men were landing the outfit, ropes were fastened between the tops 

 of some scrubby trees close to the beach and a piece of canvas spread 

 for an awning, under which the baggage was placed. An old booby 

 had her eggs in the sand within 3 feet of the edge of the sheltered area 

 and stood her ground unflinchingly while the men were at work, 

 keeping a wary eye on their movements and making vicious dabs 

 whenever a leg came incautiously within reach. Having arranged 

 camp, I went out exploring for an hour or so and returned with various 

 specimens, including the egg of a tropic bird, and found that one of the 

 boatmen had driven ofl' the booby and thrown away her eggs. Wish- 

 ing to test the bird's discrimination, I placed the reddish-brown egg of 

 the tropic bird in the hollow where the two greenish-white eggs of the 

 booby had been, and sitting under the awning began to prepare 

 specimens. In the course of half an hour the owner of the despoiled 

 nest returned and alighted 10 or 15 steps away near another deserted 

 nest, gave a look at the eggs in it, walked to still another, looked at it, 

 and then proceeded directly to her own nest and stopped. She looked 

 about and then down at the nest. The presence of the single 

 reddish-colored egg appeared to surprise her; she looked at it with 

 one eye and then with the other as if in doubt. An instant later the 

 feathers on her head and nape ruffled up and with a loud squawk of 

 rage she suddenly dashed her beak again and again into the strange 

 egg, breaking it to fragments in a moment. As soon as the egg was 

 demolished she took wing and disappeared out to sea. There was no 

 intention to sacrifice the tropic bird's egg in this experiment, so the 

 booby carried off the honors. 



About 10 o'clock the following night a visit was paid to the nesting 

 boobies. The night was calm, and taking a lighted candle I walked 



