80 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



SpHng. — The migration is difficult to trace or define, owing to the 

 wandering habits of this species, which seems to drift up and down 

 the coast in search of a food supply. A general northward or south- 

 ward movement is further obscured by the habit, common to this 

 and other shearwaters, of flying in large circles or long loops. Mr. 

 Anthony (1896&) noted that during February and March "98 per 

 cent of the black-vented shearwaters observed off San Diego were 

 flying northward, and the reproductive organs of those taken late 

 in February indicated that the nesting season was very near at hand. 

 They would have bred within two or three weeks, I think," These 

 birds were doubtless moving toward their breeding grounds at that 

 time, where they probably arrive and begin preparations for nest- 

 ing before the end of March. 



Nesting. — Mr. Anthony (189G?>) first found the black- vented shear- 

 water breeding on Guadalupe Island, " which lies about 220 miles 

 south of San Diego and about 65 miles from the nearest mainland. 

 Punta Baja, on the peninsula." He visited the island on May 15, 

 1892, and writes: 



The island is entirely of volcanic matter, huge cliffs of lava rising often 3,000 

 feet from the sea. These are honeycombed by thousands of holes and minia- 

 ture caves, offering unexcelled nesting sites for Cassin's auklet, Xantus's mur- 

 relet, and other burrowing species, including the black-vented shearwater. 



The cliffs about the North Head are all inaccessible, rising directly from 

 the water, from a few hundred to nearly or quite three thousand feet, so 

 that nothing could be learned of their nesting at that point. Three days 

 later, however, we dropped anchor in Wheeler's Bay, at the southern end of 

 the island, where the land is somewhat lower, and here a colony was found 

 near the water. The burrows were in every instance either under a huge 

 block of lava or in a crevice, where they were as much out of our reach as 

 they were in the cliffs. A few of the burrows might have been opened, pos- 

 sibly, had we been provided with crowbars and suitable tools for wedging 

 apart the blocks of lava, but after several ineffectual attempts with the tools 

 nature provided we gave up and set a few steel traps at the mouths of some 

 of the burrows in order to establish beyond dispute the identity of the species. 



Again he writes (1900) of other breeding grounds farther south: 



On the San Benito Islands, lying between Guadaloupe and Cerros Islands, 

 I have also found a few P. opisthomelas nesting. So far as I have been able 

 to discover, there are no burrows on these islands, all the nests being in small 

 caves, which are nearly filled with deposits of guano left by untold genera- 

 tions of Pufflnus. The caves are all small and the nests inaccessible, but I 

 think that each cave was inhabited by .several pairs of birds, judging by the 

 outcry and warning hisses that greeted my approach to the entrance. 



About thirty-five miles south of San Benito Islands lies Natividad Island, 

 a lower and more sandy island than those previously mentioned — a condition 

 which seems to suit the requirements of the black-vented shearwaters to a 

 nicety, for here are found thousands of them, nesting the full length of the 

 island, some three miles in extent. With the exception of a few rocky slopes 

 and ridges, the entire island may be said to be one almost continuous colony. 

 This island I first visited in August, 1S96. The size of the burrows at once 



