Previous to his departure, however, we will see them collecting in large flocks at certain places, and for once they seem eager to economise their strength, spending much of the day sitting and resting. This goes on for a few days and then suddenly they all disappear, and we shall see them no more till next spring. Where have they gone, and how? By what instinct will they find their way over hundreds of miles of sea, perhaps, for the first time, and yet again in due season return to their birthplace? By what power will they be able to undertake so long a journey and not fall exhausted on the way? Such are some of the questions that force themselves upon us, and our inability to answer them helps to keep alive that spirit of wonder and reverence for the powers of nature that is too apt to be overlooked in this matter-of-fact twentieth century. Its colour above is of a deep metallic blue; forehead and throat dark chestnut; pectoral band blue, rest of under parts buffish pink, somewhat variable in tint. Tail forked, the outermost pair much longer than the rest, and all except the central pair with white patches on the inner webs. In the female the outer tail feathers are shorter and the chestnut less intense. The young are duller, and the chestnut on the throat is very pale. Length 7·5 in.; wing 4·9 in. RED-RUMPED SWALLOW Hirundo rufula, Temminck. This species is found in Southern Europe west of Italy through Asia Minor to Persia and Afghanistan. An adult male was picked up dead on Fair Isle near the Shetlands early in June 1906. It may easily be recognised from our own Swallow in having the tail black; rump, nape and sides of neck, rusty red; and the under parts rufous finely streaked with black. Length 7 in.; wing 4·8 in. THE HOUSE-MARTIN Chelidon urbica (Linnæus) More local and less abundant than the preceding species, from which it may always be distinguished by its white rump and shorter tail, the House-Martin is nevertheless sufficiently common to be familiar to every one. In habits, except for its method of nest-building, it closely resembles the Swallow. It arrives about a week later, and stragglers may sometimes be seen even as late as November, long after the bulk of their comrades have departed. These stragglers are either family parties that have delayed their departure till the young were ready to fly, or more often inhabitants of the far north passing through on their long journey to the tropics.