276 GENERAL HABITS 



I he drumming perfonnanie unavoidably advertises the bird's whereabouts to enemies as 

 well as to others. It is significant, therefore, that a bird can stop in mid-action at anv time 

 except durino: the height of the "roll". Individuals have been seen to "freeze" in this manner 

 at the approach of a dog or upon spotting a hawk overhead. Even the faint click of a well- 

 muffled movie camera will cause this reaction. Nevertheless. man\ birds arc killed each vear 

 on their drumming logs. 



The Sound 



Many times during the Investigation, field men have mistaken the sound of a distant gasoline 

 engine or tractor for a drumming grouse. Over the vears. besides likening it to "the rapid 

 rolling of a distant drum " ', a variety of other similes have been used by different observers. 

 Thus, Lahontan"'' speaks of it as a "humming noise", and Edwards"", quoting Bartram. re- 

 ported "they sound like thunder at a distance" — a comparison which has since been made by 

 iimumerable authors. Its resemblance to the booming of a far-off gun has also been suggested. 



Ventriloquistic to a high degree, the sound is deceptive with respect to both the direction of 

 the drummer and his distance away. Over the hilly, broken terrain of most grouse coverts in 

 the Northeast, it is most often audible at distances up to somewhat over a quarter of a mile. 

 Under especially favorable conditions, however, it has been heard nearly a mile awav. The 

 direction of the sound tends to be more confusing to an observer within the woods than to one 

 in the open. Apparentlv, it echoes to some extent among the tree trunks. 



How Produced. Impelled by a certain air of mystery surrounding the performance because 

 of the wariness of the birds, observers have from the beginning attempted to explain the 

 method by which the sound is produced. Certain Indian tribes believed the birds beat upon a 

 log with their wings and thus called the species the "carpenter bird"'"". Lahontan "' thought 

 they struck "one wing against the other". Bartram"" pictured them as "clapping their wings 

 against their sides", a belief shared by Audubon"^ and \uttall"". Brooke"' suggested "they 

 swell their breasts like a pouting pigeon, and beat with their wings", but left it ambiguous as 

 to whether the wings beat upon the inflated breast or merely the air. An anonymous author in 

 American Field'"" suggested that the wings beat u|)on the inflated lungs, while another writer*''" 

 stated the sound is jiroduced h\ "inflating an air sac . . . striking it with their wings and 

 forcing the air out through the mouth". In fact. Mavnard ' excn contended it to be primarih 

 vocal and that "the wings merely aid in producing it . . . just as a rooster crows, flapping its 

 wings at the same time". In 1874. however. Brewster'' |)ublished an account of a series of 

 careful observations of a drumming grouse from a blind but 12 feet awa\ and advanced defi- 

 nitely the conclu>iiui that the sound resulted from the concussion of the wing-beats on the air 

 alone. 



So the controversy went. The "hollow log theory" was earU ilispro\ed 1>\ the fact that 

 grouse frequently drum on boulders and similar objects. Neither was any appreciable degree 

 of credence placed in the possibility that air sacs or vocal sounds were involved. On the 

 other hand, while considerable belief persisted in the theories of Lahontan and Bartram, the 

 obvious care with which Brewster's observations had been made and recorded gained wide 

 acceptance for his explanation iitilil I'JO.S. 



In that \ear Hodge' threw additional fuel on the fire b\ introducing pholograpliic e\ idence 

 which he contended showed the sound to be produced b\ "the impact of the stitlU held concave 

 wing on the feather cushions of the sides". At the same lime. Jones''" joined Brewster in the 

 lielii'f that the wings beat against nothing but air. 



