Vol. xliii.] 68 



It will be understood that on this occasion I deliberately 

 collected the clutches as laid and completed, always con- 

 vinced (and hoping) that the Screaming Cowbirds would 

 eventually occupy the nests of the Bay- wings, once the 

 opportune moment or time arrived — in which conviction 

 fortunately I was not disappointed ; the eggs, as stated, 

 being first found on the 5th of December, 1907, or at the 

 fifth attempt of the Bay-wings (both pairs) to rear their 

 young. It will also be noted that the eggs of this particular 

 Screaming Cowbird are slightly larger than those laid by 

 either of the females of the Bay-wings concerned, as well as 

 differing in form. Measurements : — 



Bay-winged Cowbird, com. variety, average 2*5 x l"175 cms. 



„ „ rare „ „ 2-5 x 1-16 „ 



Screaming Cowbird „ 2*8 X 1*1625,, 



List of Fosterers found loith Eggs of Argentine Cowhird 

 (Molothrus bonariensis). By J. M. Goodall, Oct./Dec. 

 1907 and Sept./Dec. 1912. 



No. of 

 times. 



3 Short-winged Tyrant-Bird {Machitornis rivosa). 



,3 Yellow-breasted Marsh-Bird {Pseudoleistes virescens). 



1 Yellow-headed Marsh-Bird {AgelcBus Jiavus). 



1 White-throated Spine-tail {Synallaxis albescens). 



25 White-banded Mocking-Bird {Mimus triurus). 



13 Scissor-tailed Tyrant-Bird [Milvulus tyrannus). 



12 Chingolo Song-Sparrow (Zonctrichia pileata). 



4 Red-billed Ground-Finch {Einhernagra platensis). 

 3 Lesser Diuca Finch {Dhica mmor). 



1 Scarlet Tyrant-Bird {Pyrocephalus ruhinea). 



1 Yellow-shouldered Song-Sparrow {Catwniculus peruanus). 



11 Total. 



Note. The White-banded Mocking-Bird was very abundant 

 in the Estancia " La Ethel " in 1912. 



This bird did not breed in " Los Alfalfares,'-* neither did 

 the Lesser Diuca Finch. 



