Vol. xliii.] 66 



Sparrow were short or incomplete ones in the second 

 venture. It will be of interest to note that the two females 

 in question laid respectively the smallest and most heavily 

 pigmented eggs and the largest light green speckled ones 

 encountered by me of the species, representing the extremes 

 of variation, both in size and coloration of the series collected, 

 which comprised, however, thirty-six carefully chosen clutches 

 only. The bird was very abundant in the vicinity. In (Jase 

 No. 2, sections Nos. 2, 3, 4, and Cases Nos. 4 and 5, are 

 shown eggs of the Argentine Cowbird [Molotlirus honariensis) 

 with different fosterers collected by me in the Argentine 

 Republic : in 1907 at the Estancia '' Los Alfalfares," Arias, 

 Province of Cordoba, and in 1912 at the Estancia ** La 

 Ethel," Buena Esperanza, Province of San Luis. The habits 

 and eggs of this species have been very exhaustively treated 

 of by Mr. Hudson in ' Argentine Ornithology,' vol. i. 

 pp. 72-86, and my experiences (restricted to two short 

 seasons' work) coincide with what is already known, though 

 there is reason to believe I encountered new fosterers in the 

 Red-billed Ground-Finch {Emhernagra platensis), Yellow- 

 shouldered Song-Sparrow {Coturniculus peruanns), and 

 White-banded Mocking-Bird {Mimus trhirus). Altogether 

 eleven fosterers came under my observation, list of which is 

 appended. One point, Mr. Hudson always found ('Argentine 

 Ornithology,^ vol. i. p. 154) that the Scarlet Tyrant-Bird 

 {Pyroceplialus ruhineus) deserted the nest when victimized 

 by the Cowbird, but in the one example encountered by me 

 of the nest of that bird being chosen as a foster-home, I 

 found the female Tyrant-Bird sitting contentedly on a full 

 clutch of three of her own eggs (one damaged and useless) 

 and one (a large-sized one — and these eggs differ notably in 

 size and colour) of the intruding Cowbird. 



In Section No. 1 of Case No. 2 are eggs of the Bay-winged 

 Cowbird (Molothrus hadius) and the Screaming Cowbird 

 {Molotlirus Tufoaxillaris) , these last being perhaps the first 

 collected or brought to this country. 



As is fairly well known now, the Screaming Cowbird is 

 parasitical on the Bay-winged Cowbird only, while the last- 

 mentioned, under no circumstances, allows the ordinary 



