78 U.S. NATIONAL MUSEUM BULLETIN 233 



my notice, distributed among the following areas: Ontario, Pennsyl- 

 vania (eight records), New Jersey, Maryland, Virginia, North Caro- 

 lina, Tennessee, Illinois, Michigan, Iowa, Alabama, Oldahoma, Texas, 

 New Mexico, Colorado, California, and Michoacan, Mexico. Lowe 

 (1917, p. 455) found that in Pueblo County, Colorado, the cowbird 

 appeared to rely extensively on the gnatcatcher; there "the young 

 may be seen yearly fed by gnatcatchers. It is rather strange that 

 I have never laiown them (the cowbirds) to lay their eggs in the 

 nest of any other species though they doubtless do so." In a similar 

 fashion, Ligon (1961, p. 235) reported that, in New Mexico, this 

 gnatcatcher was one of the frequent victims of the parasite; in Cali- 

 fornia, Ashworth and Thompson (1930, pp. 122-124) also found 

 these gnatcatchers rearing young cowbirds. In one case the hosts 

 raised one of their own chicks together with one of the parasite's 

 chicks. A noteworthy southern record is the one reported by Davis 

 (1953, p. 95) from Tzitzo, Michoacan, Mexico. 



Donald (1888, p. 26) reported a parasitized nest in Texas, and 

 recently Nye (in litt.) found another in the same state, containing 

 no less than 3 eggs of the dwarf cowbird and 1 of the gnatcatcher. 

 This is the largest number of parasitic eggs yet recorded for a single 

 nest of this small host. 



Occasionally, this species may cover over the strange eggs — if the 

 latter are laid before any of the host's eggs are present. Spicer 

 (1887, p. 38) at Goodrich, Michigan, found a pair of gnatcatchers 

 building a nest; eleven days later he examined the nest and found 

 that a cowbird had deposited an egg before "the owners, and that 

 they had put in more lining and covered it entirely over, and had 

 then buUt up the sides of the nest about three quarters of an inch 

 higher. ..." 



Despite the lesser frequency with which the gnatcatcher is para- 

 sitized, as compared with some of the vireos, warblers, and sparrows, 

 it has been noted as a cowbird host by such early writers as Wilson and 

 Audubon and by numerous others since then, many of whom merely 

 listed it as a known victim but gave no new instances. 



Black -tailed Gnatcatcher 



PoUoptila melanura Lawrence 



Three races of the black-tailed gnatcatcher are known to be im- 

 posed upon by the dwarf race of the brown-headed cowbird in Arizona, 

 California, Baja California, Sonora, and Chihuahua. There are, 

 in all, only 13 records with data in my fJes but, from discussion with 

 observers of long experience, it is clear that these are only a fraction 

 of the total number of such cases found and otherwise not placed on 

 record; thus, it is not possible to appraise adequately this species 



