I HAVE read in NATURE (p. 428) your correspondent's letter relative to the instinct shown by magpies in Scotland as to the time for commencing their nest-building, which goes so far as to assume that this particularly cunning bird is capable of fixing a certain day in March (the Sunday after the 16th as I remember) as the invariable time to start the nest. And the writer observes that it would be well to ascertain if difference of latitude made any difference in the magpies' calculation. Now I live in the south-east of Ireland, a good many degrees south of your correspondent's Scotch magpies' locality, and it so happens that I have for the last twenty years observed the nest-building of magpies, who have enjoyed undisturbed possession, and who invariably build in the trees close to my house. It is curious that this colony (if a single pair may so be called) never increases-four young “mags” are brought out every year—but though I have observed congregations of ten or fourteen at times, the breeding birds never exceed two. The young birds never, like rooks, join a colony near their paternal nests, but are shipped off to new localities. I could mention many traits of my magpies' instinct—“their tricks and their manners”—but will confine myself to the nest-building. They never repair or reoccupy an old nest. A new one is constructed every year, and always, each year, in a different tree. Their nest-building is a serious labour, and takes a long time. So they begin early in February, selecting the sites often with much deliberation. The work is entered on very early in the morning, and the “mags” seldom work in the daytime. About the end of March this domed nest with its two openings is finished, and the laying of eggs commenced. I am quite certain that the middle of March is not the time of beginning the nest, and this is important, as the claim set up for the magpies instinctive knowledge of dates therefore falls to the ground. I do not conceive it possible to prove that in this particular magpies have a more highly developed instinct than most other birds; all have their normal time of nesting, although there may be cases of abnormally late or early building; but as to the magpies or any other bird being able to fix dates exactly to the day, it is unproved and incredible.