446 A CURIOUS PROBLEM. 



sparrow's eggs remained, and the next day there were none. I sought in vain for them 

 on the ground in every direction. 



Having found the eggs of the Cow Bird in the nest of a yellow-throat, I repeated my 

 observations. The process of incubation had commenced, and on the seventh day from 

 the discovery, I found a young Cow Bird that had been hatched during my absence of 

 twenty-four hours, all the eggs of the proprietor remaining. I had not an opportunity of 

 visiting the nest for three days, and on my return there was only one egg remaining, and 

 that rotten. The yellow-throat attended the young interloper with the same apparent 

 care and affection as if it had been its own offspring. 



The next year after, my first discovery was in a blue-bird's nest, built in a hollow 

 stump. The nest contained six eggs, and the process of incubation was going on. Then 

 a few days after my visit I found a young Cow Bird and three eggs remaining. I took the 

 eggs out : two contained young birds apparently come to their full time, and the other was 

 rotten. I found one of the other eggs on the ground at the foot of the stump, differing in 

 no respect from those in the nest, no signs of fife being discernible in either. 



Soon after this I found a goldfinch's nest, with an egg of each only, and I attended it 

 carefully till the usual complement of the owner were laid. Being away at the time, 

 I could not ascertain precisely when the process of incubation commenced, but from my 

 reckoning, I think the egg of the Cow Bird must have been hatched in nine or ten days 

 from the commencement of incubation. On my return, I found the young Cow Bird 

 occupying nearly the whole nest, and tlip foster-mother as attentive to it as she could 

 have been to her own. 



I ought to acknowledge here that in none of these instances could I ascertain exactly 

 the time required to hatch the Cow Bird's eggs, and that, of course, none of them are 

 decisive ; but is it not strange that the eggs of the intruder should have been so uniformly 

 the first hatched ? The idea of the egg being larger, and therefore from its own gravity 

 filling the centre of the nest, is not sufficient to explain the phenomenon ; for in this 

 supposition the other eggs must be proportionably elevated at the sides, and therefore 

 have as much or more warmth from the body of the incumbent than the others. This 

 principle would simply apply to the eggs of the blue-bird, for they are nearly of the same 

 size ; if there be any difference, it would be in favour of the builder of the nest. How 

 do the eggs get out of the nest ? Is it by the size and nestling of the young Cow Bird ? 

 This cannot always be the case, because in the instance of the blue-bird's nest in the 

 fallen stump the cavity was a foot deep, the nest at the bottom, and the ascent perpen- 

 dicular ; nevertheless, the eggs were removed, although filled with young ones. Moreover, 

 a young Cow-hen finch is as helpless as any other young bird, and so far from having 

 the power of ejecting others from the nest, or even the eggs, that they are sometimes 

 found on the ground under the nest, especially when the nest happens to be very small. 



I will not assert that the eggs of the builder of the nest are never hatched ; but I can 

 assert that I have never been able to find one instance to prove the affirmative. If all the 

 eggs of both birds were to be hatched, in some cases the nest would not hold half of 

 them: for instance, those of the sparrow or yellow-breast. I will not assert that the 

 supposititious egg is brought to perfection in less time than those of the bird to which the 

 nest belongs, but from the facts stated I am inclined to adopt such an opinion. How are 

 the eggs removed after the accouchement of the spurious occupant? By the proprietor 

 of the nest unquestionably, for this is consistent with the rest of her economy. Aftei 

 the process of hatching, she is taken away by her attention to the young stranger ; the 

 eggs would be only an incumbrance, and therefore instinct prompts her to remove them. 

 I might add, that I have mostly found the eggs of the sparrow, in which were remarked 

 young ones, lying near the nest containing a Cow Bird, and therefore 1 cannot resist this 

 conclusion. 



Would the future parent feed two species of young at the same time? I believe not. 

 I have never seen an instance of any bird feeding the young of another immediately 

 after rearing their own. I should think the sooty-looking stranger would scarcely interest 

 a mother while the cries of her own offspring, always intelligible, were to be heard. Should 



