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UF study says hearing loss in stranded animals causes behavior changes

Researchers wonder whether the problem of animals adapting to new environments might be hearing related and more common than initially thought

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Megan Strobel, DVM, a graduate of University of Florida College of Veterinary Medicine, partnered with SeaWorld’s veterinary and training teams, the National Marine Mammal Foundation, the International Fund for Animal Welfare, Dolphins Plus, Dolphin Research Center, Gulf World, and Clearwater Marine Aquarium.

Several years ago, University of Florida aquatic animal veterinarian Michael Walsh, DVM, a clinical associate professor of aquatic animal health at the UF College of Veterinary Medicine, noticed a concerning pattern of two stranded dolphins after they had been rescued. Both dolphins returned to the beach once they had been released back into the wild.

While Dr. Walsh worked to rehabilitate the animals, he noticed they exhibited numerous behavioral problems. A hearing test at Mote Marine Laboratory in Sarasota, Fla., revealed one of the dolphins was completely deaf (the second dolphin couldn’t be tested), which led Walsh to wonder whether the problem of animals adapting to new environments might be hearing related and more common than initially thought.

When Megan Strobel, DVM, then a first-year UF veterinary medical student, went to Walsh, her faculty mentor, in 2013 to discuss a possible research project, he suggested that she might compare hearing capacity and behavior changes in wild and facility-housed dolphins. The result of their collaboration, which also involved numerous other individuals and organizations, was a study that appeared in the Journal of Zoo and Wildlife Medicine.

The study found that stranded animals with hearing deficits showed markedly different behaviors than animals with normal hearing and concluded that hearing assessments should be routinely administered as part of regular health examinations in all animals under human care.

Hearing is the primary sense of odontocete cetaceans, also known as toothed whales, which include dolphins, porpoises, and all other whales possessing teeth. Currently, little information on the relationship between odontocetes and hearing loss reaches those taking care of the animals, the researchers said.

Hearing loss in odontocetes can be caused by loud noises, parasites, trauma, and medical issues such as infection, just as it can in humans. But the loss of sonar capability, which relies on hearing, is especially difficult and traumatic for the wild individual, Dr. Strobel said.

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“If we recognize that all animals will lose hearing over time, then putting technology such as the auditory evoked potential test we used into their health exams as they get older will help everyone understand how their sensory systems are doing,” said Walsh.

For animals that have grown up in facilities, the environment is known and their daily lives are somewhat predictable, he said.

“But if you change the environment on a deaf animal, it’s similar to changing the environment on a human individual,” he added. “They have to give more effort to understanding the new environment and what it means.”

The researchers felt it was important to educate caretakers about challenges the animals face in situations where hearing deficits in older animals or deafness may result in behavior that is misunderstood.

Just like people, all animals as they age can potentially lose some of their senses, like hearing and sight. The long-term health and wellness assessments of those creatures should include the same considerations as would be applied to an older human being, the researchers said.

“And for their cohorts in the wild, we need to understand the implications of hearing loss so we can approach those animals differently at a time they are trying to adapt to a rehabilitative environment with the loss of their most important sense,” Walsh said.

To make the project work, Strobel partnered with SeaWorld’s veterinary and training teams, the National Marine Mammal Foundation, the International Fund for Animal Welfare, Dolphins Plus, Dolphin Research Center, Gulf World, and Clearwater Marine Aquarium.

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