DETECTION OF AIRCRAFT.
[To TRE EDITOR opens " SPECTATOR")
Salk—The suggestion in a letter in your last week's issue as to grey shrikes being used for detecting aircraft is very interesting, but I fear that in practice it would be found a failure. Although I have never kept grey shrikes, yet for a good many years past I have been interested in noticing how various birds regard objects passing in the sky over their heads. My demoiselle cranes are very quick to notice birds flying over their enclosure at a great height, especially herons, which, when almost mere specks, they will notice and greet with loud cries. They are even more excited when swans fly over, but I have never noticed them peculiarly on the alert to detect aeroplanes, though of course somewhat excited when one passes over them at a moderate height. They had some considerable experience of this before the war. It is interesting to note that they will often turn an eye upward and greet with loud croaks the sun when just emerging from a cloud. Their greatest excitement, however, is always reserved for the time when atmospheric conditions give an echo to their own cries. On such occasions a demoiselle crane will continue calling at intervals for half an hour. The Sarin crane and the crowned crane seem to be less concerned than the demoiselle with anything passing overhead. Cayenne spur-winged plover are exceedingly quick to notice anything passing overhead, and greet it with loud cries. They can, I feel sure, readily distinguish at great distances their near relation, the English lapwing, from other birds. Some peen; ago when I kept Icelandic ptarmigan I on one occasion found them crouching paralysed with terror, the reason for which was clear when I detected a kestrel hovering at a great height over an adjacent field. The ptarmigan had evidently mistaken this for an Icelandic falcon, that arch-fear of their own country. There is no doubt to my mind that birds have very great faculties for detecting enemies at a distance, but for human beings to attempt to use these faculties for their own ends would be to employ a most uncertain instrument.—I am,
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