Humming in bears: a peculiar sustained mammalian vocalization

Abstract

2007. Humming in bears: a peculiar sustained mammalian vocalization. Acta Theriologica 52: 379-389.A peculiar sustained vocalization has long been known under various names in several bear species but not been studied in sufficient detail. Based on a critical survey of the relevant literature, analyses of tape recordings and pertinent own observations we tried to clarify the presence of this vocalization in the species of the Ursidae as well as its structural characteristics and specific mode of sound production. To avoid confusion with other vocalization types we introduce the term humming for it. Furthermore we discuss its communicatory and functional significance and formulate hypotheses as to its evolutionary origin against the background of acoustic communication signal repertoires known in the terrestrial Carnivora. Humming is present in all extant species of the Ursidae with the exception of the giant panda. It has similar structural characteristics and the same mode of sound production in all species. It is also known in adult bears but its occurrence is largely restricted to cubs. Humming is a synapomorphic vocalization type of the Ursidae which is not phylogenetically related to another vocalization type known in the terrestrial Carnivora. It is a rapid sequence of very short single sounds; long bouts of sustained exhalatory sound production are interrupted by very short inhalatory phases without sound. Both the sound and the body vibration accompanying its production are highly likely to be communication signals. Yet, controlled physiological experiments on bear mothers and cubs are still necessary to formulate and test specific hypotheses as to the communicatory function and adaptive significance of humming.

The influence of ambient noise on maternal behavior in a Bornean sun bear (Helarctos malayanus euryspilus)

“…While we could not reliably measure nursing behavior visually in this study, the elevation in the humming vocalization suggests that cub increased its effort to nurse. However, because the precise communicative function of the humming vocalization is not known [Peters et al, ], and because the elevation in cub vocal output was not significant, we interpret these results cautiously.…”

“…The “hum” vocalization, in particular, is markedly different than the rest of the cub's vocal repertoire. Humming is a rhythmic, persistent and relatively low frequency vocalization [Peters et al, ]. While most vocalizations are presumed to convey varying degrees of need or distress (i.e., are “plaintive”), the humming vocalization is generally associated with nursing [Derocher et al, ], however the precise communicative function of this vocalization is unknown [Peters et al, ].…”

Fellatio in captive brown bears: Evidence of long‐term effects of suckling deprivation?

“…In the case reported here, the provider may have found a substitute for teat-sucking that also resulted in a let-down of substitute "milk." Notably, this animal emitted the same humming sound used by suckling bear cubs, thought to be linked to milk let-down and to signal the cub's comfort and contentment either to the mother or to itself [Peters, Owen, and Rogers, 2007], suggesting that this bear retained infantile behavior. The fact that this behavior persisted so long, remained one-sided, was not influenced by the presence of a female bear, and did not result in or reflect any other obvious social hierarchy among the two bears makes this case particularly interesting.…”

Behavior in Free-Living American Black Bear Dens: Parturition, Maternal Care, and Cub Behavior

“…On our occasional visits to maintain the webcams, the bears recognized and accepted our presence. If the mothers were nursing cubs, as evidenced by the pulsing hum vocalization of suckling cubs [ 35 ], the mothers did not move. If the mothers had their heads tucked under their chests tending to cubs, they seldom looked up.…”