Page:Condor21(1).djvu/34

 Jan., 1919 PARASITISM. OF NESTLING BIRDS BY FLY LARVAE 33 had been without food for a number of days and many of them were only half grown. At first the nestlings showed some ueasiness by shaking themselves, but this only lasted for a minute or two, after which they again came to complete rest. They were observed from time to time until about 8:30 in the evening, but there was nothing unusual in their behavior. At about three o'clock the next morning I was suddenly awakened by a thud in the cage. My first thought was that the mother bird had become frightened and had jumped from the nest; but when I looked, I found one of the nestlings down below. I was still more sur- prised to see the others, including the old bird, sitting on the rim of the nest and not huddled closely together in the center. When I picked up the nestling which bad leaped down, I noticed two maggots crawling about at the bottom of the cage, but upon examination found no naggots on the bird itself. The two maggots. which had been dragged down by the nestling--it being impossible for them to get out of the nest-box in hny other way--were not full-grown and were gorged with blood. Thereupon the four remaining birds were carefully examined. I now saw what I had been expecting to see: A number of maggots were clinging to the feet and lower parts of the body of each one of the nestlings. None were .found on the mother bird. Most of these maggots released their hold while the birds were being examined, but some of them had to be forcibly de- tached. These, like those found at the bottom of the cage, were not full-grown but were filled with fresh blood. No marks, visible to the naked eye, could be seen where the maggots had pierced the skin of the birds, nor were any traces of blood apparent. This .was conclusive proof that the sticky material found at the bottom of infested nests is not coagulated blood which has dripped from the wounds made by the maggots, but faeces deposited by the latter. The four nest- lings were then transferred to another nest and their own carefully examined. Sixty-eight maggois were taken from the nest, showing that the nest had origin- ally harbored twenty-eight. More than half of the sixty-eight maggots showed traces of fresh blood, the smaller ones being most gorged. The soft cotton lining of the nest-box was then removed and carefully examined, but no additional maggots were discovered. Thereupon the box was refilled with cotton and the nestlings put back. The latter now appeared completely at ease. They again huddled closely. together as formerly, the .mother bird sitting on them during the night. I)uring the next few days a number of other experiments were carried out with thi brood of goldfinches. While one of them was being held in the hand a few vigorous, half-grown maggots were placed among the nestling's feathers. After crawling about among them for a brief period, the maggots would invaria- bly drop from the bird. One evening several dozen half-grown, hungry maggots were placed in a pasteboard box and covered with a layer of soft cotton about an inch thick. Two of the nestlings were then transferred to this box and the lat- ter covered up. In less than ten minutes eight or nine of the maggots were found firmly, attached to the nestlings, ingesting blood, only a few releasing their hold while the' birds were being examined. This same experiment was tried the fol- lowing afternoon, but, strange to say, none of the naggots were attached to the birds. But when this experiment was repeated the same evening, and on subse- quent evenings, some maggots were again found clinging to the nestlings. This indicates that they do their deadly work at night and rest in the lower parts of the nest during the day. It is interesting to note that' both of the nestlings which