Primary Feathers in Flight. 147 



primary (1) is emarginate only on the posterior web, and the 

 fifth primary (5) emarginate only on the anterior web, while 

 the three other primaries (2, 3 and 4) are emarginate on both 

 webs. The sixtli primary (6) is not emarginate and is shown 

 for comparison. The emarginate contour of the anterior web 

 is sometimes called " sinuate. "* When the primaries are in 

 their natural places in the wing the emargination of the ante- 

 rior web in every case exactly corresponds to the emargination 

 of the posterior web of the preceding feather, and permits 

 the feathers to be easily and firmly interlocked at the points on 

 the webs where the emarginations begin. (See a and ft, fig. 1.) 

 This correspondence is characteristic and demonstrates the 

 inter-relation of emarginate primaries. 



To illustrate the way in which primaries are interlocked, 

 the five outer primaries of a Red-shouldered hawk are shown 

 as they appear when they are not interlocked, as seen from 

 beneath the wing, in fig. 2, and then as they are when inter- 

 locked in fig. 3. The same set of primaries as seen from above 

 the wing are shown in figs. 4 and 5. 



The primaries may be more widely separated than they 

 appear in these figures and yet be firmly interlocked, espe- 

 cially in the case of large birds where the feathers are long in 

 proportion to their rigidity. Under these circumstances the 

 emarginate portions of the primaries are usually curved slightly 

 upward by the pressure of the air. This upward curve has 

 often been observed. 



II. Observations made at New Haven, Conn., showing the 

 Interlocking op Primaries in Certain Species. 



In September, 1891, during the hawk migrations of that 

 year, about thirty hawks were killed, examined as soon as 

 they had fallen to the ground, and the number of primary 

 feathers interlocked recorded. These observations are given in 

 Tables I and II, in which the columns marked A and B refer 

 to the wings of the bird, because the wings were not designated 

 by "right" and "left" when the observations were made. The 

 hawks were shot as they were passing over a high hill south- 

 east of New Haven, Conn. 



Large migratory flights of hawks have occurred along the 

 coast of Connecticut nearly every autumn, the greatest flights 

 having taken place in September. On numerous occasions 

 many thousands hawks have passed during a day, when flocks 

 of upwards of one hundred of certain species have been 

 observed. In the opinion of the writer, the time of these 

 extensive migratory movements is directly dependent upon the 

 direction and velocity of the wind. If the wind starts to blow 



* E. Ccraes, Key to N. Aruer. Birds. 



