138 Vol. XX 



THE YOLLA BOLLY FOX SPARROW 



By JOSEPH MAILLIARD 



AS WE BECOME better acquainted with the genus Passer ella we find it 

 proving to be one of the most plastic forms of our North American avi- 

 fauna. It bids fair to rival even the Melospiza group, which has been split 

 up into subspecies from so many different localities that it is hard to keep track 

 of them. It has been said that we have song sparrows described from every 

 marsh in California ! While this is not literally true, there certainly are re- 

 markable differences in a great many instances, and we are finding the same 

 sort of thing in the fox sparrows. 



For some years students interested along these lines, especially observers on 

 the Pacific coast, have been sorely puzzled by the differences among individual 

 specimens of Passerella found in winter in the same localities. These differ- 

 ences were such as could only be accounted for upon the hypothesis that they 

 indicated separate forms, each with its definite breeding ground, and not that 

 they were individual variations of any one race. As time goes on and we have 

 more numerous and widespread records, with more detailed observations, we 

 are discovering that this hypothesis is the correct one. 



Readers of The Condor may remember that their attention was called to 

 the occurrence in winter in Marin County, California, of a very large-billed fox 

 sparrow which seemed more nearly related to the Stephens Fox Sparrow (Pass- 

 erella iliaca stephensi) than to any other known form (Condor, xiv, March, 

 1912, p. 63). Alternative explanations of this occurrence were that either there 

 was an undiscovered race closely approaching stephensi breeding somewhere to 

 the north of Marin County, which it visited in winter ; or else, contrary to the 

 rule that in the northern hemisphere birds do not winter north of their breed- 

 ing range, these individuals were actually examples of stephensi which had 

 straggled northward in the winter season. At the time I first took up this mat- 

 ter the only specimens of stephensi available for comparison were in worn sum- 

 mer plumage, while the Marin County birds were in bright new feather. This 

 made the comparison very unsatisfactory, in that the difference in color might 

 be accounted for by this fact. Measurements of parts unaffected by wear were 

 practically identical in the two lots. This Marin County form was again men- 

 tioned in The Condor, xv, March, 1913, p. 93. 



Since that time material has been accumulated in the way of 

 breeding birds obtained in Trinity and Tehama counties, California, by col- 

 lectors from the Museum of Vertebrate Zoology of the University of Califor- 

 nia, which proves that there actually is a race of fox sparrow breeding to the 

 north, as already suspected. But this form, for want of sufficient material for 

 seasonal comparison, was still linked up with stephensi of southern and south- 

 eastern California. Recently, however, Mr. H. S. Swarth of the Museum of 

 Vertebrate Zoology, has become interested in the status of the Passerella group 

 and has gotten together a large number of specimens for comparative study. 

 While working over these he came across just the sort of material needed to 

 put together the chain of evidence in favor of the distinctness of this new form, 

 and kindly notified me of the fact, we having often discussed this matter to- 

 gether. As he is working out the status of the subspecies of Passerella on this 



