Animal Tales

Giving A Hand for Heart-Healthy Bonobos


Milwaukee County Zoo staff performs an echocardiogram (ultrasound of the heart) on Brian the bonobo in 2014. The Zoo is now able to perform echocardiograms on many of the bonobos while they’re awake.

Zuri the bonobo is an easy-going, quiet guy. He’s not a leader of the bonobo group at the Milwaukee County Zoo, but he’s as active as a typical bonobo, says Stacy Whitaker, lead bonobo keeper. You might not guess he was diagnosed a few years ago with heart disease. In fact, he might not be alive today if not for the Zoo’s work studying heart disease in great apes. The Zoo was a founding partner of the Great Ape Heart Project (GAHP) and the first zoo to train bonobos for “awake” – without anesthesia – echocardiograms and blood-pressure readings. Through this work, Zoo veterinarians discovered Zuri’s heart problems. With daily medication, he remains a healthy 19-year-old bonobo.

“Twenty years ago, sudden death was often the first and only sign of heart disease in great apes,” says Dr. Marietta Danforth, GAHP project and database manager. “Today, through routine cardiac health screenings, we are able to detect and treat heart disease and reduce sudden cardiac-related mortalities.”


Zuri the bonobo presents his finger to zookeeper Stacy Whitaker and veterinary technician Bob Korman so they can take his blood pressure.

Zuri’s diagnosis didn’t come as a surprise – his father died from a heart condition at age 14, quite young for a species that can live 40 years or more in captivity. In fact, cardiovascular disease is remarkably common in bonobos and other great apes. About 45% of captive bonobos that live past the age of 1 die from heart problems, says Dr. Vickie Clyde, Milwaukee County Zoo veterinarian. The disease often strikes males early, with many of them dying in their 20s or 30s.

At least, that’s how it used to be. But Clyde and Zoo staff are contributing to the effort to slow the progression of cardiovascular disease, improve quality of life and extend lifespan in affected apes. The latest piece of that effort is a grant allowing the Zoo and its partners to study bonobo genetics and evaluate diagnostic tools such as finger blood-pressure cuffs.

Clyde has been collecting information about bonobo heart health since 2005 as the veterinary advisor to the Bonobo Species Survival Plan®, which manages captive bonobos in North American zoos. At the same time, the veterinary advisor to the Gorilla Species Survival Plan was collecting similar information. Their efforts became the basis for the Great Ape Heart Project based at Zoo Atlanta in 2010. Since then, the project has expanded to collecting heart data for chimpanzees and orangutans as well as gorillas and bonobos. Nearly every institution in the Association of Zoos & Aquariums that houses great apes participates, Danforth says.


Clyde and her team, including Zoo veterinary technician Bob Korman, local cardiologist Dr. Sam Wann and cardiac sonographer Leann Beehler, recognized the importance of measuring the bonobos’ heart health often. That meant training the animals to get blood-pressure readings and echocardiograms (ultrasounds of the heart) while awake instead of putting them under anesthesia. Blood-pressure cuffs placed around the arm didn’t work because the bonobos would panic when the cuff tightened. “We assumed they felt like they were being grabbed, so they instinctively pulled back,” Clyde says. Instead, the team has trained 14 of the Zoo’s 21 bonobos to sit for blood-pressure readings using a finger cuff, which doesn’t cause as much alarm. “These finger cuffs really don’t feel like anything,” Korman says. “Even the really skeptical bonobos, after they feel it, they’re fine with it.”

The GAHP hopes to confirm that finger cuffs are an effective way to measure bonobos’ blood pressure through a three-year grant from the Institute of Museum and Library Services. The grant, now in its second year, has provided finger cuffs to the six other institutions in North America that house bonobos. With the additional data, the GAHP hopes to establish more reliable baselines for normal bonobo blood pressure.

After years of practice, the staff at the Milwaukee County Zoo has refined the process for taking bonobos’ blood pressure. They start by simply putting the cuff on the bonobo’s finger and letting the animal get used to the machine. In future sessions, the staff increases the pressure on the cuff, offering food rewards such as grapes for good behavior. One of the main challenges is getting the bonobos – especially the younger ones – to sit quietly for the procedure. “If you get a bonobo to sit still, that’s amazing,” says Whitaker, the bonobo keeper. Laura, the oldest bonobo in the group at age 50, is the best at keeping still for the readings, and younger bonobos learn from her, Korman says. “They just stick their fingers out,” he says. “It’s amazing. They see it and they imitate it.” As part of the grant, the Milwaukee County Zoo and GAHP have created a video to train other zoos in taking finger-cuff readings.

The data from these readings help zoos understand more about heart disease in bonobos and how to treat it. “We want to identify who’s at risk, treat them if they are at risk and help them live long, high-quality lives,” Clyde says. Affected bonobos are typically treated with human medicine, but veterinarians don’t always know how much to give them. The finger-cuff readings help the veterinarians determine if the medications are working or if the dosage needs to be adjusted.


Dr. Sam Wann (left), a cardiologist, and Leann Beehler (second from left), a sonographer, serve as advisers to the Great Ape Heart Project and have volunteered many hours working with the Milwaukee County Zoo’s apes. Here they take an echocardiogram of Tommy the orangutan.

The grant also allows the Milwaukee County Zoo and the Medical College of Wisconsin to look at bonobos’ genes to learn about the genetic causes of cardiovascular disease. Dr. Melinda Dwinell, associate professor of physiology at the college, says the team has mapped the genomes of three bonobos already – a father, mother and child – and plans to map six more. “We hope to identify some variants that are present only in the bonobos with cardiovascular disease that can be used to screen living bonobos and predict if they are at risk of developing the disease,” she says. “If they are at risk, it might be possible to treat them before they show signs of disease or alter their diet and environmental conditions to reduce the likelihood of mortality.”

The project still has much to learn about heart disease in bonobos and other great apes, including why the disease is so prevalent and how it differs from heart disease in humans. But it has made great strides that have benefited Zuri and many other apes. Zuri already has lived five years longer than his father and shows no sign of slowing down. “That’s a victory,” Whitaker says.

By Stacy Vogel Davis

From the Winter 2018 issue of Alive