they return, but, as is the case with the small birds at the stacks, not in nearly so instantaneous or simultaneous a manner; and this may be repeated for a greater or lesser number of times. All the remarks that I have made in regard to this phenomenon in the case of other birds apply equally here, perhaps, indeed, to a greater extent; for, as remarked, at the moment of each sudden exodus a certain number—sometimes about half—of these sand-martins will be more or less hidden within the holes they are excavating, yet out they all dart with the rest. Such sudden flights and disappearances for a few minutes, after which all come back, strike me as being extremely curious.
Sand-martins appear to be pugnacious. Indeed, they sometimes fight fiercely, and I have seen two, after closing with a sharp, shrill "charr" and struggling in the air for a little, roll down the steep declivity of sand in which the perpendicular face of the pit often ends. It, therefore, seems the more curious that they allow their holes to be taken possession of by sparrows (and, also, by tree-sparrows)—without offering any resistance. I have seen one of the latter birds sitting quietly and calmly in the mouth of a hole, whilst a pair of martins, who had, probably, excavated it, hovered excitedly just over and about him, but without doing more. On many other more or less similar occasions there has been excitement on the part of the martins, but never an attack. Yet a tree-sparrow, or even a sparrow, is not such a very much larger and stronger bird than a sand-martin, and, considering the numbers of the latter, as well as their greater activity and powers of flight, it seems to me an odd thing that they should submit to such a
