poraneous but not necessarily the correlated exemplar of the species concept). This 

 tendency to vary, which is manifest in the egg, might conceivably, indeed would in 

 all probability, reflect itself racially (or somatically) under selective breeding, which 

 in the case of the California Jay has marvelously preserved the uniformity of the 

 species. 



There exists upon the Island of Santa Cruz, some twenty-five miles distant from 

 the mainland at Santa Barbara, a Jay, Aphelocoma insularis, which is almost an exact 

 replica of the mainland bird, A. californica, in color and pattern of plumage, but which 

 has undergone certain important modifications of proportion, especially of beak and 

 feet. While the wing and tail measurements of the island bird average only from ten 

 to twenty per cent longer than those of the mainland type, the bill will sometimes 

 bulk nearly twice as large, and the feet and tarsi will probably show a fifty per cent 

 increase in bulk. The Santa Cruz Island Jay enjoys a fairly uniform distribution 

 within its narrow range, an area twenty-five miles long by eight wide at the widest 

 point; and because it is a vigorous, dominant form upon the island, is probably main- 

 tained at the saturation point of some 2000 or 3000 pairs. 



As in the case of any other insular species, questions arise as to the presence of 

 this jay on Santa Cruz Island. How did it get here? How long has it been here? 

 What was the size of the original colony? Has there been an infusion of new blood 

 from time to time derived from the mainland? or has there ever been such infusion? 

 These are very natural and very interesting questions, but their answer is quite beyond 

 the power of the anatomist. The "skin-man" is silent. He has no criteria beyond 

 that of somatic change in one direction, i. e., increase in size, to guide him. He is 

 destitute of the knowledge of any other factor by which he may check up or correlate 

 his guesses. 



Naturally, the taxonomist turns to the geologist. He is able to help out some- 

 times, but his answers are apt to be a little vague. For how long a period has Santa 

 Cruz Island been separated from the mainland of California? "A hundred thousand 

 years," says Mr. John R. Pemberton, who has done a great deal of topographic work 

 for the U. S. Geological Survey in this section. That is a generous allowance, more 

 than ample to account for this increase of the bird's bulk. But are there any other 

 possibilities besides this of original occupancy by which this semi-distant island might 

 have been stocked? Yes, three at least; and in naming them we shall rule out of 

 present consideration the "obvious," but also impossible, hypothesis of flight. The 

 wings of a jay, whether insularis or californica, are too short and weak to permit of 

 its attempting a sheer flight of twenty-five miles. The jays of Santa Cruz,' if not 

 actually autochthonous, are colonists, and their immigration must have been assisted 

 either by storm, or by drifting wreckage used as a refuge, or by human agency. 

 Either one of these, or else the migration occurred at a time when the channel which 

 separates the island from the mainland was much narrower than at present. 



A consideration of the soundings of the Santa Barbara Channel might be instruc- 

 tive here, but it would lead us too far afield for our present discussion. The point is 

 that the anatomist unaided is absolutely helpless in trying to answer these questions. 

 He cannot tell whether the Santa Cruz Island Jays are a split-off branch of the 

 mainland stem, resident for a hundred thousand vears, or whether they were carried 

 over a few thousand years ago by the Indians. He cannot tell whether they are the 

 motley residue of a familiar traffic between island and shore, which finally ceased only 

 when the channel became too wide to cross conveniently awing, or whether, indeed, 

 the place was peopled by a chance pair blown over in a storm. 



At this point the oologist comes in. He does not pretend to know all about it, 

 but he is able to make a modest contribution to knowledge. At least he feels compe- 

 tent to circumscribe the area of this inquiry. A series of some fifty sets of eggs of 

 the Santa Cruz Island Jay passed in review by the Museum of Comparative Oology 

 shows them to be the most absolutely uniform of any spotted eggs known. The series 

 is practically without deviation as to ground color; and while there is inevitably some 

 difference in the distribution of the spots, there is no substantial deviation in the color 

 of the pigment. 



If this series had to be compared with a mainland series, showing also a sub- 

 stantial uniformity, we should be as far at sea as the anatomist; but when we place 

 this series alongside one accumulated on the mainland shore, only twenty-five miles 

 away, we find the most startling contrast. The eggs of Aphelocoma insularis are 

 among the most homogeneous known; the eggs of A. californica exhibit the highest 

 degree of habitual variation of any passerine species in North America. There can be 

 only one meaning to this. A. insularis does not represent a general derivation or 

 stock from the mainland, nor could it have achieved such a uniformity if it had been 

 variously derived. The Santa Cruz Island Jays represent a single Mendelian type 

 accidentally derived from one of the multitudinous strains existent on the mainland. 

 We have in their eggs an example of purest inbreeding, an exact selection; and the 

 birds are in all probability the offspring of a single original pair. There have been 



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