Author Archives: vgarduno

The Better to Hear You With? Noise Mitigation in Captive Environments

By Victoria Garduno

African Cheetahs are facing one of the most dire extinction crises in the world today. Zoos and sanctuaries around the globe have been working tirelessly to try and protect them, first by navigating them through arguably one of the worst genetic bottlenecks we have seen to date, and now by carefully walking the tightrope that is captive cheetah breeding. Suffice to say, captive cheetahs are delicate creatures [1]. So you can imagine my surprise when, on a recent trip to Busch Gardens Tampa, I discovered that they had built a brand new roller coaster attraction…..which passed less than 100 yards from their cheetah enclosure.

Busch Gardens2

Portion of Busch Gardens Park Map, with cheetah enclosure in blue, and coaster passby in red.

 

The average roller coaster produces sound at anywhere from 40 to 90 decibels as it passes by an observer. This is about as loud as a jackhammer, and just shy of the point where hearing loss occurs in humans. In fact, the most noise is measured from the side of the cars, rather than the front or back[2], which means that the position from which the cheetahs, or any other animal which may be exposed, experiences the noise is actually the most extreme position, acoustically speaking. However, noise in captive situations is not limited to places which employ ride attractions. Many popular zoos have music and performance attractions, which, with the use of microphones, speakers, and amplifiers, are more than capable of producing enough sound to affect the captive environment. In some cases, the noise output from concerts or performances may even exceed the level produced by ride attractions.[3] Research has shown that zoo animals can be affected even by the crowds that visit them, showing increased vigilance and movements in response to escalating crowd noises.[4]

Chart showing relative decibel levels of common sounds.

Chart showing relative decibel levels of common sounds.

So then, what may be done in terms of noise mitigation? Continuing with my Busch Gardens case study, I secured an audience with a senior cheetah keeper at the park, who was able to shed some light on what had been done in this particular situation to reduce the effect of the coaster noise on the cheetahs. Surprisingly, most of the measures employed were behavioral. The most important part, she said, was done even before the cheetahs arrived in Tampa, when they were still at the sanctuary where they were received from, in Africa. Recordings of the cars going by on the track were made, and sent over to the sanctuary, where they were played for the cheetahs who were slated to take up residence at the park. This effectively habituated them to the type and level of the noise that they would experience, and decreased any negative effects which could be caused by sudden or unexpected exposure. Additionally, the recordings could be played softly at first, and then increased in volume to real-life levels once the cheetahs were comfortable. In other cases, habituation has been shown to reduce stress and startle responses in animals, both captive and wild, however, stress levels may remain elevated [5].

cheetah rest

In terms of sound design, clever engineering may be employed to reduce noise levels and reduce stress on captive animals. In the case of the roller coaster, there are many techniques which reduce noise, including filling the track with sand or vermiculite, and the addition of walls, buildings, or tunnels to absorb sound. These approaches may reduce the sound produced by ride attractions by as much as 20 decibels [6]. Additionally, animal enclosures also play a role in dampening sound. The shape of an enclosure has been shown to affect the type and level of sound that reaches the occupants, as well as the addition of trees, water features, rocks, and ‘ambient’ or ‘natural’ sounds. Exhibits which feature plexiglass fronts are also extremely effective against crowd noises, as those tend to be directionally oriented at the front area of an exhibit.[7]

sound2

In the case of the Busch Gardens cheetah coalition, this story does have a happy ending. Until recently, no cheetah participating in an animal ambassador program had ever had a successful litter. That changed in November of 2014, when one of Busch Gardens’ ambassador cheetahs, who had been previously housed at the park, produced a healthy litter of four cubs, two of which remain at the park. It would appear that the sound mitigation techniques, both behavioral and structural, were successful in reducing stress sufficiently for the cheetahs to feel comfortable enough to breed. If these methods are successful in cheetahs, it is probably safe to assume that they will also be successful in other, less fragile species. If we can implement these measures in zoos and sanctuaries across the globe, we may be able to improve the welfare of captive animals everywhere, and maybe even save ourselves a headache or two as well.

New arrivals!

New arrivals!

[1] O’Brien, S., M. Roelke, L. Marker, A. Newman, C. Winkler, D. Meltzer, L. Colly, J. Evermann, M. Bush, and D. Wildt. “Genetic Basis For Species Vulnerability In The Cheetah.” Science: 1428-434. Print.

[2] Menge, Christopher W. “Noise from Amusement Park Attractions: Sound Level Data and Abatement Strategies.” Noise Control Engineering Journal: 166. Print.

[3] “Sound Advice Note 10.” – Rock and Pop. Ed. David Adams. 1 Jan. 2007. Web. 26 Mar. 2015.

[4] “Zoo Visitor Effect on Mammals: Does Noise Matter?” Applied Animal Behavior Science 156 (2014): 78-84. Print.

[5] Knight, Richard L. “Responses of Wildlife to Noise.” Wildlife and Recreationists Coexistence through Management and Research. Washington, D.C.: Island, 1995. Print.

[6] Davis, Joshua I., Charles Birdsong, and Harold Cota. “Vibroacoustic Study of Circular Cylindrical Tubes in Roller Coaster Rails.” Noise Control Engineering Journal: 333. Print.

[7] AZA Ape TAG 2010. Chimpanzee (Pan troglodytes) Care Manual. Association of Zoos and Aquariums, Silver Spring, MD. 1.4 “Sound and Vibration”