HOST RELATIONS OF PARASITIC COWBIRDS 191 



suggests a less close and accurate coordination between the ovulation 

 of the parasite and the nestmg activity of the prospective hosts. 



The point is an important one, and to emphasize it, by contrast, 

 we may cite one of Hann's conclusions (1941, p. 220) from his careful 

 and protracted study of the brown-headed cowbird in relation to the 

 ovenbird, Seiurus aurocapillus, in Michigan. He foimd that the 

 female cowbh^d made regular inspection trips to nests dming the 

 absence of the o^\^lers, between the time of first discovery of the nest 

 and the time of her o^^^l egg-laying, and that she seemed to know in 

 advance where she was going to lay. This is certainly a contrast to 

 the condition of misplaced ovulation we have just described in the 

 shiny cowbird. 



A further consideration emerges from these data. There is some 

 reason to think that in a parasitic bu'd with well-marked individual 

 host specificity, such as the Em'opean cuckoo, the individual hens lay 

 their eggs in nests of the same species of host as those by which they 

 themselves were reared. A cuckoo raised by a meadow pipit later 

 tends to lay its eggs m meadow pipits' nests, while another individual 

 that has been reared by a hedge sparrow uses nests of that species 

 for its own eggs. There is no evidence of a comparable degree of obli- 

 gate host restriction in the shiny cowbu'd although there is what 

 appears to be a high degree of it in the ancestral screammg cowbu'd 

 stock. The habit of chopping eggs indiscriminately on the gromid, 

 not even in a nest at all, or of using old deserted nests clearly suggests 

 the absence of any trace of a tendency toward host specificity. The 

 inference here is clearer and more du^ect than in the more usual in- 

 stances of nest parasitism by this cowbu'd, as in the bulk of those 

 cases we have no evidence to suggest or to dismiss the possible effect, 

 or even existence, of ontogenetic host preference. 



One other relative imperfection — like the preceding, also a source 

 of loss to the parasite and not to its hosts — is the lack of "understand- 

 ing" or the lack of proper attunement in conniiunication between 

 the alarm calls of the hosts and the response of the parasite durmg 

 its nestling and early fledgling stages. When danger in the form of 

 a hawk or other predator threatens, the young cowbird appears to 

 be unaffected by the seemingly obvious distress calls of its foster- 

 parents. Instead of crouching quietly, it clamors noisily for food as 

 if no peril were imminent. This often results in its being captured 

 and eaten by the instigator of the alarm it failed to comprehend. 

 Many years ago Hudson commented on this in central eastern Argen- 

 tina, and I had essentially the same experience in the same and other 

 parts of that country. Hudson noticed that in his area a large pro- 

 portion of the nests of the cachila pipit, (Anthus correndera were para- 

 sitized, but that it was a rare thing to find a young fledgling cowbird, 



