STRAY NOTES ON BIRDS. 69 



Straij Notes on Birds. 

 By C. F. M. SwYNNERTON, C.M.B.O.U., F.E.S., F.L.S. 



Nightjars. 



When a nightjar is settled, even conspicuously, in a path or 

 open road, it is not easy to t-jU until one approaches it closely 

 whether the dark object is a niobtjar, a "cow-pat," or a 

 stone. But let it rise, and the white tips or outer webs o£ 

 the outer tail-feathers at once shine out as the bird, itself 

 invisible, now against the nearer landscape suddenly spreads 

 its tail in flio-ht. I have found myself able to differentiate 

 our commoner local species of (Japrimui gus at night by 

 means of the difiPerences in these tail markings, and it is 

 likely enough that they are useful to the birds themselves 

 for recognition purposes. 



Now, why do nightjars make a habit each night of settling 

 on the open ground between their flights at insects ? I 

 think that one has only to recollect how at night one ducks 

 down instinctively and remains squatted, when watching a 

 bird or insect that is invisible except when seen against the 

 sky, in order to know the reason. I tested this view when 

 it occurred to me some years ago by watching nightjars for 

 several nights in succession in an open road on which they 

 were numerous, and I came to the conclusion that it was 

 probably the correct one. The bird uses the ground as its 

 perch in order to be able to detect its prey against the sky. 



One other question is worth asking. Why the noiseless 

 flight of nightjars ? That of an owl is intelligible, for the 

 small mammals that form its principal prey would be 

 friglitened to cover by wings that were noisy. But Coprid?e 

 and cockchafers don't worry about noises, and if you find a 

 bunch of bananas or a mass of fallen peaches covered with 

 the wariest of Noctuid moths, you may shout and clap your 

 hands at them and fail to make them budge. Do owls attack 

 nightjars ? That might be a reason for noiselessness. It is 

 possible that they do occasionally take one, but I have found 

 no such remains in any owl's stomach, and I have watched one 

 owl(Bubo maculosus) perched on a dead stump and intently 



