by careful consideration of existing facts. It seems safe to prophesy that certain 

 apparently anomalous occurrences now on record will find their explanation in con- 

 ditions that were overlooked at the time those observations were made. It is evident 

 from Mr. Dawson's evidence, from the record by Alexander Walker in The Condor 

 (vol. 16, 1914, p. 94) which first gave Dawson his clue, from the statements in Grinnell 

 and Storer's "Animal Life in the Yosemite" (pp. 373-374), and from additional corrob- 

 orative facts that I have found in the collection of the Museum of Vertebrate Zoology, 

 that Empidonax griseus is an upper Sonoran and Transition Zone species, confined in 

 the breeding season mainly to sagebrush surroundings in the Great Basin. Empidonax 

 wrighti nests mainly in the Canadian Zone, occasionally in the Hudsonian Zone, from 

 southern California north at least to extreme northern British Columbia. Any appar- 

 ent overlapping of breeding ranges (as is claimed to occur in the White Mountains) 

 is doubtless to be explained either by the upward extension locally of lower zones, thus 

 carrying griseus to an altitude where wrighti usually breeds, or else as an unwar- 

 ranted assumption of nesting from the mere occurrence of birds (juvenal or adult) 

 outside their normal nesting ground. — H. S. Swarth, Museum of Vertebrate Zoology, 

 University of California, Berkeley, April 21, 192i. 



