Texas researchers have made a first step in looking for clues to improve rhino reproduction in captivity by investigating noises present in zoo habitats.
The soundtrack to a wild rhinoceros’ life is wind passing through the savannah grass, birds chirping, and distant animals moving across the plains. But a rhinoceros in a zoo listens to children screaming, cars passing, and the persistent hum of urban life.
A group of researchers from Texas believes that this discrepancy in soundscape may be contributing to rhinos’ difficulties thriving and reproducing in captivity. During the 168th Meeting of the Acoustical Society of America (ASA), which is held 27 – 31 October at the Indianapolis Marriott Downtown Hotel, they will present their acoustical analysis of a captive southern white rhinoceros habitat, a first step towards understanding the impact of noise on these endangered animals.
Though zoologists have studied the impact of factors like diet and hygiene on rhino reproductive health, sound has been largely ignored. However, rhinoceroses have some of the keenest senses of hearing in the animal kingdom, able to perceive infrasonic sounds below the frequency range of human range of hearing. In the wild, they can sense predators coming from miles away by the vibrations their footsteps send through the ground. Because rhinos are so sensitive, noise that humans don’t notice – or can’t even hear – could be distressing and disruptive to them, negatively impacting their health, said Suzi Wiseman, a bioacoustician at Texas State University.
Wiseman and colleagues at University of Texas at Austin and Baylor University used sound detectors strategically placed around the rhinoceros enclosure at Fossil Rim Wildlife Center near Glen Rose, Texas to record different frequencies of sound that the animals encountered over the course of a week.
The about 700 hectare conservation park, located about an hour and a half drive from Dallas, is further removed from urban life than most zoos. “But when you start recording [the noises], you start to notice them on all sides. You’re really showing up with a constant infrasound the whole time,” added Wiseman.
Much of the noise recorded at Fossil Rim was natural in origin – wind, birds, and other animals at the site. However, the researchers also identified noises from a nearby road, jet planes passing overhead, and park staff and visitors. Infrasonic noise was persistent across all recordings, though its sources have not yet been fully identified.
So far, the researchers have only analysed one soundscape and so cannot conclude the specific impact it might have on the rhinoceroses. However, they plan to record sounds from more zoos and parks, looking for a connection between particular types of noise and animal health. It is likely that urban zoos would have more noise from human origins than the relatively remote facilities that have traditionally had the greatest success in breeding captive rhinos, Wiseman said.
“One of my questions is if there’s a continuum – from natural soundscape on one end to completely urban, completely anthrophonic – then is there somewhere along that continuum where an animal, particularly a rhinoceros, stops being healthy?” said Wiseman.
The researchers hope their work will help zoos develop optimal habitats for animals, often a challenge given tight space and limited budgets.
Still, Wiseman said, there are simple steps zoos can take to reduce ambient noise and improve quality of life for their inhabitants. For example, placing sound-absorbing barriers around enclosures and replacing noisy zoo vehicles with quieter electric ones both make a big difference at a relatively small cost. Zoos planning major renovations could consider more ambitious strategies, such as choosing to house large, sound-sensitive animals in more rural locations, where animals would have more space and less exposure to city noise.
The abstract of ASA meeting presentation “What comprises a healthy soundscape for the captive Southern White Rhinoceros (Ceratotherium simum simum)?” by Suzi Wiseman, Preston S. Wilson and Frank Sepulveda:
Many creatures, including the myopic rhinoceros, depend upon hearing and smell to determine their environment. Nature is dominated by meaningful biophonic and geophonic information quickly absorbed by soil and vegetation, while anthrophonic urban soundscapes exhibit vastly different physical and semantic characteristics, sound repeatedly reflecting off hard geometric surfaces, distorting and reverberating, and becoming noise. Noise damages humans physiologically, including reproductively, and likely damages other mammals. Rhinos vocalize sonically and infrasonically but audiograms are unavailable. They generally breed poorly in urban zoos, where infrasonic noise can be chronic. Biological and social factors are studied but little attention if any is paid to soundscape. We present a methodology to analyse the soundscapes of captive animals according to their hearing range. Sound metrics determined from recordings at various institutions can then be compared and correlations with the health and wellbeing of their animals can be sought. To develop this methodology we studied the sonic, infrasonic and seismic soundscape experienced by the white rhinos at Fossil Rim Wildlife Center, one of the few U.S. facilities to successfully breed this species in recent years. Future analysis can seek particular parameters known to be injurious to human mammals, plus parameters known to invoke response in animals.
(Source: Acoustical Society of America meeting press release via Newswise, 24.10.2014)