70 U.S. NATIONAL MUSEUM BULLETIN 233 



case both kinds of eggs were ejected by the catbh'ds. More recently, 

 I have tried the same experiment with a robin's egg and a mourning 

 dove's egg, and again the catbird threw them out while, at the same 

 time, another catbird's egg was accepted. A catbird's egg, however, 

 on which small specks and blotches were painted was rejected. Nut- 

 tall (1840, p. 380) observed more than a century ago that other birds' 

 eggs Avere "almost instantly ejected" from catbird nests. 



Nickell's studies (1958, p. 286) of about 3,000 nests of the catbird 

 in southern Michigan, over a period of 30 years, revealed that only 

 eight nests were parasitized, or about 1 in every 375. "Six nests held 

 one cowbird egg each at the time of discovery, and one held two eggs 

 of the parasite. . . . All cowbird eggs had disappeared from five nests 

 in less than a day from the time they were laid, one egg disappearing 

 in less than an hour after being deposited." 



A relatively few species of victims have been reported to bury cow- 

 bird eggs by building a new nest floor or wall over them. Among 

 such species is the catbu'd; one occurrence, a nest with a cowbird egg 

 covered over in the lining, was found at Cranbrook, Michigan (Detroit 

 Audubon Soc, 1953, p. 74). More recently, the McGeens (1962, pp. 

 116-117) reported another instance, also in Michigan. 



Occasionally, however, cowbird eggs are accepted and the parasitic 

 chicks are reared by the catbird. Elder (1921, p. 185) reported that 

 he had known a catbird to raise one or two of its own young along 

 with a young cowbird. Recently, Nickell (1958, p. 286) reported a 

 cowbird reared to the fledgling stage by a catbu'd in Michigan. 



Some 26 actual instances of cowbu'd parasitism on this species have 

 come to my attention, in addition to a number of indefinite statements 

 or mere listings. These records come from Quebec, Maine, Massachu- 

 setts, New York, New Jersey, Pennsylvania, Maryland, Indiana, 

 Michigan, Minnesota, Iowa, Kansas, Missouri, and North Dakota. 

 Two subspecies of the parasite, the nominate race and the northwestern 

 M.a. artemisiae, are involved, the latter race in the North Dakota 

 records, the former in all the others. In the great majority of these 

 cases, only 1 cowbird egg was found in the nest, but in Nelson County, 

 North Dakota, on June 14, 1901, A. C. Bent collected a set containing 

 1 egg of the catbird and 4 of the cowbird, the latter apparently laid 

 by two different individuals. Van Winlde (1890, p. 48) found a nest 

 with 4 eggs of the catbird and 2 of the cowbird. A similar set, also 

 in Michigan, was found by Berger (1951c, p. 117). This was the only 

 parasitized nest out of 71 examined by him. 



If the proposed races of the catbird, rujricrissa and meridianus, 

 should be accepted by the next checklist, the present records would 

 include both the nominate carolinensis and meridianus. 



