278 GENERAL HABITS 



Thus reopened, the dehate rontinued. The next important rontribution was that of Vree- 

 land"^' who. after walching a grouse drum at close ranjip and securing a series of photographs. 

 reached the conclusion that the wings "did actually strike behind the drummer's back", which 

 was supported by Beck'" who also used the sensitized |)late. The latter writer termed the 

 sound "|)ercussion music". Then in 1923, Sawyer'™ reported on a study made during the 

 spring of 1921. After watching over a hundred drummings, he became convinced that the 

 sound is produced by the wings striking the air alone. 



Such was the status of the problem when the senior author began photographing drumming 

 grouse in 1927, three years before the Investigation was inaugurated. During that and suc- 

 ceeding years, a wealth of material, both in the notebook and on movie film, has been gath- 

 ered. In addition to the observation of wild birds, there has been abundant opportunity to 

 study individuals in captivity at the Research Center. The data assembled fiirlher attest the 

 fundamental correctness of the conclusions of Brewster and Sawyer, as do. also, the excellent 

 motion pictures of A. A. Allen. 



With respect to the sound itself, the authors believe that it represents the concussion of the 

 air filling in the vacuum created 1>\ the powerful forward, upward and somewhat inward 

 stroke of the wing followed by its instantaneous reversal of motion. The reaction is some- 

 what akin to that which produces a clap of thunder or the crack of a whip. In creating a 

 sufficient displacement of air, the concave nature of the underside of the wing, together with 

 the angle at which it is held, are undoubtedly of great importance. 



Purpose 



An attribute of the male grouse only, drumming is fundamentally a corollary of courtship 

 and functions to announce the whereabouts of vigorous cocks both to females and to other 

 males. Called "tlic throbbing heart, as it were, of awakening spring'"", it is indulged in 

 most commoidx' during the early breeding season. On the other hand, it has been heard every 

 month of the year and often becomes quite frequent in the early fall. In the spring, it may 

 serve either as an invitation to the female or as a challenge to the world in general. At other 

 seasons, it undoubledly represents an expression of exuberatice on the |i;irt of an utiusually 

 vigorous individual. 



The Drumming Season 



Over most of New York, the drumming season begins in late March and reaches its height 

 during late April and early May. At the higher elevations in the northern part of the State, 

 the kettledrums commence a week or so later. Observation of grouse in captivity at the Re- 

 search Center reveals that they must learn to drum. Apparently they instinctively know the 

 motions but, even after acquiring adult ])luinage. require considerable practice to develop 

 the ability to drum with tin- normal sound effect. On several occasions young males, which 

 never attempted to drum wliilc in a mixed grou|). have been placed in individual pens with 

 the coming of spring. These birds have usually jiroceeded to give a perfect drumming per- 

 formance excejjt that there was little sound. A biid reported by Allen" took two weeks to 

 learn. Thus, it might Ix- that the staggered dates on which one first notices various wild birds 

 commencing to drum may be due. in jjart. to tlie young birds in the population, although the 

 comparative vigor of vaiioiis individuals is probaliK llic prirnaix reason. 



TTie predominant drumming periods during llie spring are earl\ morning and late after- 

 noon. Beginning usuall\ ucll before daylight. iIk- performance is repeal<"d with remarkable 

 regularity until sunrise or somewhat thereaflcr. Mlbongh at the height of the season inter- 



