I was not fortunate enough to detect any flashing of the white throat, as described by Preble (1902: 42).
Another silent signal is a most peculiar sprawling posture of the hind legs, attained by thrusting one of them well out to one side and setting the foot down. The legs are not then symmetrically placed; the one not moved obviously bears most of the weight of the hind quarters. I managed to film this stance in a buck standing on a sky-line on August 24 (cover). On September 9 another buck assumed the posture while looking over our camp from a ridge on the opposite side of Windy River. According to Charles Schweder, this is an expression of suspicion or alarm, designed to communicate the same feeling to other Caribou. When the others notice it, they stop and assume the same pose; it may be observed in does and even fawns. Charles added that the tail is erected at the same time—a very natural accompaniment, though I failed to notice it.
In all the literature on the Barren Ground Caribou, I have found just one reference to this posture, and that a distinctly fragmentary one:
“While [the Caribou are] thus circling around I have often been amused at the manner in which they carry one hind leg. A novice in the hunting field, after having fired a shot in their direction, would think that he had broken one hind leg of each member of the herd.” (A. J. Stone, 1900: 53.)
The author makes this observation just after mentioning a herd sighted near the shore of Franklin Bay. A virtually identical posture in the Norway Reindeer has been sketched by Seton (1929, 3: 112, pl. 18), who labels it “surprize.” An analogy to the posture of the Caribou might be found in a hand thrust out, with fingers spread, by a military scout as a signal of warning or caution to his fellow scouts. A sprawling leg is perhaps the nearest approximation to the human signal that a Caribou can attain.
As noted in the section on Gaits, an alarmed Caribou may set off by taking an initial leap into the air. According to Dugmore, such an act on the part of the Newfoundland Caribou plays an important role in its system of communications, not by means of sight or sound, but through the olfactory sense. He observes (1913: 89-90):
“For hours afterwards every Caribou, on arriving at the place where the frightened ones had jumped, has started violently, and has on nearly every occasion turned and run in a manner that showed every indication of fear, even though my presence was entirely unknown to them. My idea is that when the animal is suddenly frightened it expels a certain fluid from the glands in the foot, and that this fluid is a signal of alarm, a silent and invisible warning, but none the less so positive that none dare ignore it.”
As for the foot click—a presumptive means of communication (cf. Seton, 1929, 3: 69; Jacobi, 1931: 212-216)—I must confess that I was always so engrossed with photography whenever the Caribou were close at hand (up to within a dozen feet) that I had no thought of this phenomenon and did not detect it.
References.—Richardson, 1829: 242; A. J. Stone, 1900: 53; Preble, 1902: 42; Seton, 1929, 3: 105; Murie, 1939: 245; Harper, 1949: 230; Banfield, 1951a: 19, 27.