THOUGH the singular habits of the parasitic cow-birds (Molobrus Itonariensis and M. badius) are well known to ornithologists, Mr. L. E. Miller has been able to add still further to the records of their eccentricities in a valuable paper published in the Bulletin of the American Museum of Natural History, vol. xxxvii. His observations were made during a recent expedition to Bolivia and north-western Argentina, where he found, these birds in considerable numbers foisting their eggs upon numerous species of small t>irds, especially finches. But for choice they seem always to prefer the mud nests of the oven-bird (Fur-narius). These seem to have an irresistible and fatal attraction for cow-birds, since all the eggs deposited therein appear invariably to be destroyed by the desertion of the intended dupes, which, whenever they discover the trick that has been played upon them, cover up the eggs with a layer of nesting material, refusing to incubate. In some nests layer after layer of eggs were thus found, but no young were ever met with. The numbers of eggs found in such nests ranged from six to as many as thirty-seven! While this stupidity reduces the numbers of the parasites, it at the same time reduces the number of oven-birds, which, in the areas explored by Mr. Miller, failed to produce offspring. Judging from the coloration of the eggs, Mr. Miller estimated that in some cases as many as thirteen birds may use the same nest. The egg_s of a third species (M. rujoaxillaris) were also occasionally found in these nests.