438 f'HILOSOPHlCAL TRANSACTIONS. [aNNO I788. 



nest, incubate its eggs, and rear its own young ? There is certainly no reason 

 to be assigned, from the formation of this bird, why, in common with others, it 

 should not perform all these several offices ; for it is in every respect perfectly 

 formed for collecting materials and building a nest. Neither its external shape 

 nor internal structure prevent it from incubation ; nor is it by any means in- 

 capacitated from bringing food to its young. It would be needless to enumerate 

 the various opinions of authors on this subject, from Aristotle to the present 

 time. Those of the ancients appear to be either visionary, or erroneous ; and 

 the attempts of the moderns towards its investigation have been confined within 

 very narrow limits ; for they have gone but little farther in their researches than 

 to examine the constitution and structure of the bird, and having found it pos- 

 sessed of a capacious stomach with a thin external covering, concluded that the 

 pressure on this part, in a sitting posture, prevented incubation. They have not 

 considered that many of the birds which incubate have stomachs analogous to 

 those of cuckoos : the stomach of the owl, for example, is proportionably capa- 

 cious, and is almost as thinly covered with external integuments. Nor have they 

 considered that the stomachs of nestlings are always much distended with food ; 

 and that this very part, during the whole time of their confinement to the nest, 

 supports, in a great degree, the weight of the whole body ; whereas, in a sitting 

 bird, it is not nearly so much pressed on ; for the breast in that case fills up 

 chiefly the cavity of the nest, for which purpose, from its natural convexity, it 

 is admirably well fitted. 



These observations, I presume, may be sufficient to show that the cuckoo is 

 not rendered incapable of sitting through a peculiarity either in the situation or 

 formation of the stomach ; yet, as a proof stijl more decisive, I shall state the 

 following fact. In the summer of the year 1786, I saw, in the nest of a hedge- 

 sparrow, a cuckoo, which, from its size and plumage, appeared to be nearly a 

 fortnight old. On lifting it up in the nest, I observed 2 hedge-sparrow's eggs 

 under it. At first I supposed them part of the number which had been sat on 

 by the hedge-sparrow with the cuckoo's egg, and that they had become addle, as 

 birds frequently suffer such eggs to remain in their nests with their young ; but 

 on breaking one of them I found it contained a living foetus ; so that of course 

 these eggs must have been laid several days after the cuckoo was hatched, as the 

 latter now completely filled up the nest, and was by this peculiar incident per- 

 forming the part of a sitting-bird.* 



Having under my inspection, in another hedge -sparrow's nest, a young cuckoo, 

 about the same size as the former, I procured 2 wagtail's eggs which had been 



• At this time I was unacquainted with the fact, that the young cuckoo turned out the eggs of the 

 hedge-sparrow ; but it is reasonable to conclude, that it had lost the disposition for doing this when 

 these eggs were deposited in the nest. — Orig. 



