SAFETY DEVICES IN BIRDS WINGS — GRAHAM 



303 



considering the fitting of some form of aid to control and lift. As 

 all airplanes are, in effect, gliders with motors in the place of 

 gravity to give them forward movement, the same thing should 

 apply to them as well. 



SUMMARY 



The connections between the ways of birds in the air, their size, 

 the shape and loading of their wings, the presence or absence of slots, 

 and, when present, their development, are so intricate that many 

 years of investigation would be required before really satisfactory 

 conclusions could be reached. 

 The surface of the subject has 

 only been scratched in this 

 paper, but it is hoped that the 

 scratches will have indicated 

 the amazing width of this 

 field for research and the pos- 

 sibility of the riches that may 

 be found in it. For what they 

 are worth, the observations, 

 theories and tentative conclu- 

 sions which have been men- 

 tioned are summarized below. 



1. Wing-tip slots are 

 formed by the gaps 

 left between the emar- 

 ginated tips of the 

 flight feathers of a 

 fully spread wing. 



2. They vary in 

 number, if present at 

 all, from one to eight, and in size from nearly half the length of a 

 wing to mere vestiges. 



3. Their presence appears to depend primarily on the proportion- 

 ate length of the wings of a bird and on the shape of their tips. 

 Short wings, with rounded or square tips, have the greatest number 

 and the highest development of these slots. Long, narrow, pointed 

 wings have none. 



4. By doing away with mutual support between feathers, slots 

 form an automatic antistalling device, which appears to work in 

 somewhat the same way as the Handley-Page slotted airplane wing. 



5. Wing-tip slots increase lateral control at low air speeds. 



6. They reduce the losses in efficiency of a wing that are due to 

 the spilling of air over the tip. 



FiGDRB 40.— Meadow-pipit about to alight to 

 feed a young cuckoo. The wrist-slots arc 

 open. (Sketched from a photograph) 



Figure 41. — Great black-backed gull ; on left, with the 

 wrist-slots open and, on the right, closed. (Sketched 

 from photographs.) 



