Myopic and occasionally ornery, rhinoceroses are like the grandfathers of the African plains. But, unlike most grandpas, they communicate by poop and also have an incredible sense of hearing.
And when captive rhinos are subject to the noise of human activity, the sounds picked up by their sensitive ears may get in the way of their sex lives. "Hearing is acute;" wrote the American Society of Mammologists of white rhinos in 1972, "the ears move constantly and independently." Bioacoustics experts at Texas State University and Baylor University recently recorded the ambient noise near a rhino enclosure in suburban Texas, picking up a panoply of sounds that rhinos might find strange - and detrimental to their reproductive health.
Though the park seemed tranquil to the scientists - it's about 80 miles outside of Dallas - the threshold for rhino hearing is lower than ours. "You go there and it feels really quiet, and most people aren't aware of the noises," Suzi Wiseman, a bioacoustics expert at Texas State University, said in a statement. Not so for the rhinos: "You're really showing up with a constant infrasound the whole time."
The sultry baritone of Barry White these sounds were not: the rumble of a plane, passing cars, the voices of park staff and visitors. Wiseman and her colleagues caution that the results, presented Friday at an Acoustical Society of America conference, consist of only one zoo and have not made a concrete link between rhino reproductive health and too much noise. They point out, however, that noise can adversely affect human reproduction.
"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?" Wiseman says.
Considering the toll that poaching and habitat loss have taken on rhinos - white rhinos, for example, are listed as a near-threatened species by the IUCN - captive breeding programs offer a way to ensure the next generation of the animals. Rhinos have, historically, been reluctant to mate while in human care. Wiseman suggests that zoos could opt for quieter electric vehicles and erect sound-absorbing barriers near sensitive creatures. And preserving wild rhinos in their natural habitats is, of course, a crucial aspect of long-term conservation.