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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 
eliffs 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 notes 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 californica), 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 odlogical 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 
