LIFE HISTORIES OF NORTH AMERICAN DIVING BIRDS. 185 



Islands, but we found plenty of murres, mostly of this species, on 

 the perpendicular cliffs at the north end of St. Matthew Island. 

 Although the murre colonies at Bogoslof Island were the most exten- 

 sive I had ever seen and probably included the greatest number of 

 birds, they were totally eclipsed in density by the wonderful colonies 

 on Walrus Island. This is a most remarkable little island, an 

 ornithological wonderland, where 10 species of sea birds breed in 

 countless multitudes, far surpassing anything I have ever seen. The 

 California murres rank first in numbers, literally covering the low 

 cliffs and rocky shores all around the island, as well as large spaces 

 on top of it, with dense masses of birds sitting remarkably closely. 

 They were exceedingly tame or stupid and would allow a near 

 approach; but if hard pressed, they would rise on their toes and 

 waddle off, flapping their wings rapidly. The clatter of many hun- 

 dred pairs of wings increasing to a deafening roar, they would pour 

 off in streams, stumbling over each other as they scrambled down to 

 the water, pattering over its surface to join the distant rafts of 

 murres on the water or diving straight downward and flying away 

 rapidly below the surface. Among the many thousands of Cali- 

 fornia murres with which the island was mainly populated we 

 noticed a few of the thick-billed Pallas's murres, which could be 

 easily recognized by their blacker heads and stockier build. The 

 relative abundance and distribution of these two species on this 

 island seems to change from time to time, for Dr. F. A. Lucas (1901) 

 writes : 



Mr. William Palmer uotes that at the time of his visit in 1890 these birds 

 were mostly on the western side, while on the east and south were the legions 

 of the California murre (Uria troile calif ornica), but no such striking peculiar- 

 ity of distribution was noticed by our party, nor were the California murres 

 much in evidence. 



Eggs. — The description already written of the eggs of the common 

 murre will do equally well for the eggs of this subspecies for there 

 is no constant difference between the two, except a slight average 

 difference in size. Both are subject to almost endless variations in 

 ground color and pattern of markings. Mr. W. L. Dawson (1909) 

 says on this subject : 



It would appear highly probable that this variety is introduced by nature to 

 facilitate recognition on the part of the birds, whose property might otherwise 

 become hopelessly confused or lost. Certainly no two adjacent eggs are 

 exactly alike, and the differences are usually so striking that a birdless ledge 

 looks like an oological bouquet. These differences, moreover, are probably con- 

 stant as between given birds. At least we found by experiment in 1907 that if 

 a handsomely marked egg were removed, another of the same type might be 

 expected in its place from one to three weeks later. 



The measurements of 74 eggs, in the United States National Museum 

 collection average 82.2 by 50.2 millimeters; the eggs showing the 



