Re: At what frequencies do Grizzly bears and Black bears hear?

Greetings,
This was a tough question, but, I was able to use the internet to find 
your answer, with many thanks to the following sites.
 http://
www.bowhunting.net/bearhunting.net/bear2.html

Bears probably hear in the ultrasonic range of 16-20 megahertz, perhaps 
higher." "The grizzly’s ense of hearing is far more sensitive than man's," 
writes Thomas McNamee in Grizzly Bear, "and it is undoubtedly an important 
aid in the pursuit of such subterranean prey as gophers, ground squirrels, 
mice, and voles, which grizzlies locate blindly and pounce on with 
noteworthy accuracy."

"At 300 meters [328 yards]," write Shepard and Sanders, "the bear can 
detect human conversation, and it responds to the click of a camera 
shutter or a gun being cocked at 50 meters [54.7 yards]."

 http://
www.inco.com/invest/voisey/mine-mill/chap17/chap17.htm 

17.2.2 Noise and Visual Disturbance

Black bears living in the Landscape Region will experience some noise 
disturbance from activities during all phases of Project development. 
Previous research
(Sopuck et al. 1979; DND 1990; RRCS 1994) and observations of bear 
behaviour during VBNC studies and exploration activity (drilling, 
helicopter overflights and
human presence) (JWEL 1997) suggests that black bears will avoid certain 
parts of the VBNC Claim Block (e.g., quarries and open pit). 

Research on the response of bears to noise indicates that bears are likely 
to show a startle response when alarmed. With few natural enemies, the 
response of black
bears to noise is likely to vary. They may be confused if approached by a 
potentially threatening object. Since bears are omnivores, they are 
considered to be less
sensitive to high frequency sounds than carnivores, which depend on 
hearing to detect prey (RRCS 1994). 

Noise modelling was undertaken by VBNC to predict noise levels resulting 
from Project activity within the VBNC Claim Block (Morrison Hershfield 
1997). The
average sound over a 24-hour period is known as the equivalent sound level 
(LEQ) and was projected for construction and operation phases. 

The loudest noise from Project activities will be from blasting. Blasting 
will result in a 24-hour LEQ peak greater than 100 dB that will extend 
over bear habitat,
including three known den sites. Experience at Cold Lake in Alberta, 
indicates that black bears are capable of habituating to either constant 
or periodic noise
(Sopuck et al. 1979). It is anticipated that the association of a warning 
noise before each blast will reduce any startle effect for wildlife. 

Projected 24-hour LEQ values will not exceed 50 dBA in the vicinity of 
other activity (excluding blasting) during construction or operation. For 
example, in the
vicinity of the airstrip and approach corridors, 24-hour LEQ values is 
estimated at 35-45 dBA. During black bear field studies in the vicinity of 
the VBNC Claim
Block, bears were observed to not react to approximately 50 percent of 
helicopter over-flights during the summer of 1996. For those that did 
react, the degree of
reaction varied but was considered strongest (e.g., flight response) 
amongst females with cubs (JWEL 1997). Displacement or short-term 
avoidance of habitat will
occur as a result of helicopter and aircraft traffic, but is not expected 
to result in any measurable effect on physiology or reproductive success. 

Denning could be affected by noise associated with Project activities. 
During denning, bears are totally dependent on fat reserves and use the 
reduced energetic
costs of torpor and thermal insulation of the den to survive. Disturbance 
(e.g., noise) during this phase of the life cycle could have much greater 
costs in terms of
survival and reproduction than at other times of the year (Tietje and Ruff 
1980; Linnell et al. 1996). 

Disturbed bears are more likely to vacate den sites than undisturbed bears 
(Tietje and Ruff 1980; Goodrich and Berger 1994). Female bears have been 
observed to
abandon dens more readily than males. Bears disturbed during the fall, 
through handling by researchers, were reported to have lost more weight 
than undisturbed
bears, although no overwinter mortality or reduced reproduction was noted. 
Researchers handling bears during mid-winter have reported den abandonment 
and a
subsequent energy disadvantage or cub abandonment (Goodrich and Berger 
1994). Once bears have emerged from their dens, they are unlikely to 
abandon their
cubs due to disturbance (DND 1994).