36 CALIFORNIA ACADEMY OF SCIENCES. 



escape the gulls. If the young when crowded off a shelf 

 by the parent falls upon another rock it is quickly followed 

 by the old bird, who broods over it until another oppor- 

 tunity and another shove launches the j^oung one in the 

 water. 



The parents share equally the duties of incubation, one re- 

 maining on the egg during the day the other by night. During 

 the day few are seen flying unless disturbed by the eggers or 

 the report of a gun, but when the relief is made morning 

 and night they are especially noisy, quarreling and scream- 

 ing in great masses of bird life. 



The young sea lions have a great fondness for murre's 

 eggs, and as soon as they are large enough to know what an 

 egg is, and once get the taste of them, they become another 

 factor in the destruction of eggs. Mr. Emerson has seen 

 young sea lions with their muzzles slabbered with egg. The 

 old sea lions do not trouble the rookeries, but spend their 

 time ashore basking about the water's edge. 



The island mule has also found that eggs make an agree- 

 able variation to his diet. He hunts nests very assiduously, 

 growing fat and sleek in the breeding season. 



The large series of eggs of this species in Mr. Emerson's 

 collection exhibits a wide range of variation in coloring, they 

 being specimens selected from thousands. In size, fifty 

 ordinary sized eggs average 82.9 x 50.8 mm. The following 

 measurements show the extremes of normal specimens which 

 were examined, 92x53; 91x51; 85x54; 85x63; 79x47; 

 77x47; 75x49; 75 x 50.5 millimeters. 



Some diminutive eggs, and those noticeably of different 

 shape or size, measured 95x46; 87x45; 77x48; 73x46.5; 

 68x44.5; 63.5x37; 60 x 38.5 millimeters. 



6. Larus glaucescens. 



Glaucous-winged Gull. — A few were seen about the 

 island as late as May. 



