BELL'S VIREO 261 



last statement. The evidence seems to indicate that the vireo will 

 usually desert the nest, if imposed upon by a cowbird. George A. 

 Moore (1928) writes from Stillwater, Okla. : 



We found ten nests, all constructed in the same manner and of much the same 

 material. All were located within one hundred yards of the first one found. 

 One nest had a Cowbird egg only ; one had a vireo egg and a Cowbird egg ; one 

 had a vireo egg; another had two dead vireos (young) and one vireo egg that 

 had not hatched ; the others were empty. From all appearances the nests were 

 all built that season. One nest was so high in a slender bush that we could not 

 see into it. 



The incident suggests to me tlie possibility that Bell's Vireo leaves its nest 

 when bothered by the Cowbird, moves over to a new site and builds a new nest. 

 There were only the two vireos in the ravine. 



Harold M. Holland writes to me from Galesburg, 111. : "Cowbirds 

 are responsible for the abandoning of many nests, and I rather believe 

 that the Bell's contribution toward increasing our cowbird population 

 may be considered relatively small." 



Pitelka and Koestner (1942) write: "Both incubating adults and 

 young apparently suffer infestation by the northern fowl mite, Lip- 

 onissus sylmarum (Can. & Franz.). On July 2, the adult bird on 

 nest No. 4 pecked and scratched its breast while on the nest. The 

 mites were numerous on the following day wiien the young hatched. 

 A heavier infestation was recorded at the nest of pair B, containing 

 three young on July 11; on July 14, two young left the nest and a 

 third was found dead in the nest. On July 15, the rim of this nest 

 and adjoining twigs were covered with 'thousands' of mites which 

 dropped to the ground in a continual little shower." 



Range. — Western United States south to El Salvador. 



DISlTtlBUnON 



Breeding range. — Bell's Vireo breeds north to north central and 

 southeastern California (Red Bluff and the Mount Lassen region, 

 Owens Valley, and Death Valley) ; southern Nevada (Ash Meadows) ; 

 central Arizona (Fort Mojave, Fort Verde, Salt Eiver Wildlife Eef- 

 uge, and the Graham Mountains) ; specimens have been collected in 

 April at St. George, southwestern Utah; southern New Mexico (Gila 

 Eiver and San Antonio) ; extreme eastern Colorado (Holly, Wray, 

 and Julesburg) ; has been reported from Wyoming (Freezeout Moun- 

 tains) ; central northern Nebraska (Thedford and Valentine) ; south- 

 eastern South Dakota (Yankton, Sioux Falls, and Dell Rapids) ; 

 southern Minnesota, casually (Minneapolis and Winona) ; southern 

 Wisconsin (La Crosse and Madison) ; and northeastern Illinois (Chi- 

 cago). East to eastern Illinois (Chicago, Urbana, and Fox Prairie) ; 

 western Tennessee (Memphis, one record) ; east-central Arkansas 

 (Stuttgart) ; eastern Texas (Marshall, Houston, Corpus Christi, and 

 Point Isabel) ; and central Mexico (Jacala, Hidalgo). South to cen- 



