Primary Feathers in Flight. 167 



VIII. The Wear of the Primaries as seen by the Micro- 

 scope. 



The primaries of a number of hawks killed when their 

 plumage was at various stages of wear, were subjected to, 

 microscopic examination. In this way it was hoped to deter- 

 mine if the primaries had become worn by habitual inter- 

 locking, or by the absence of any wear to find an argument 

 against any such interlocking, 



It was found that the wear of the extreme edge of the pos- 

 terior webs of the emarginate primaries began very shortly 

 after they had completed their growth, that is, after the moult. 

 Also that a general breaking of the feather structure all along 

 the edge of the webs in most cases obscured any special wear 

 at any particular place. In a number of cases, however, the 

 webs of the feathers, where the webs touched when inter- 

 locked, were completely broken down, apparently showing 

 wear from constant contact or pressure. Owing to the uncer- 

 tainty of this evidence, no further observations were made. 



IX. Final Summary and Conclusions. 



The most salient facts established in this paper are as fol- 

 lows : 



(1) Of over thirty hawks killed while in coasting flight, 

 which were examined immediately after they fell, in every 

 case some emarginate primaries were interlocked (several 

 slightly wounded birds not included). In the case of 27 spec- 

 imens of one species, 175 out of all emarginate primaries (270) 

 were found to be interlocked, or about 65 per cent. Other 

 observations agree approximately with this ratio. Many 

 hawks, including seven species not recorded in this paper, 

 have been shot and found with their primaries interlocked by 

 the writer and others. There is, therefore, conclusive evidence 

 that when hawks are killed while in flight, of certain types, a 

 large percentage of the emarginate primaries are found firmly 

 interlocked. 



(2) The webs of emarginate primaries of hawks that have 

 just been killed show well-defined "notches" where the edges 

 of the interlocked webs have rested against one another. The 

 facts determined by a long continued study of the formation 

 of the notches are these : 



(3) The notches formed by artificially interlocking the pri- 

 maries are identical with those found after birds are killed and 

 which are always present when the primaries are found inter- 

 locked. 



