INSIDE THE LARGEST KOALA COLONY IN THE U.S.

Expert insights from: Nicki Boyd, San Diego Zoo Wildlife Alliance general curator and Jennifer Moll, lead wildlife care specialist, San Diego Zoo 

Photo courtesy of San Diego Zoo Wildlife Alliance

San Diego Zoo is home to the largest koala colony in the United States, and one of the largest outside of Australia. These iconic Australian marsupials thrive here because San Diego’s climate mirrors their homeland. That lets the zoo grow fresh eucalyptus onsite, so its koalas always have a buffet of their favorite food. Through the newly established Association of Zoos and Aquariums’ (AZA) Saving Animals From Extinction (SAFE) Koala program, San Diego is leading U.S. conservation efforts to help ensure these threatened animals will thrive for years to come. 

Key takeaways 

• The San Diego Zoo is home to 21 koalas, the largest colony in the U.S. and the largest outside Australia and China. 
• San Diego’s Australia-like climate lets the zoo grow eucalyptus onsite, something most zoos can’t do. 
• The zoo leads the AZA’s new SAFE Koala program and funds conservation work in Australia to protect koalas in the wild. 
• Koalas are listed as vulnerable and face growing threats from habitat loss, wildfires, invasive pests and disease. 

Koala quick facts 

• Common name: Koala 
• Scientific name: Phascolarctos cinereus 
• Animal group: Mammal 
• Mammal type: Marsupial 
• Habitat: Eastern Australia eucalyptus forest 
• Lifespan: 10 to 15 years in the wild 
• Diet: 1 to 1.5 pounds of eucalyptus leaves each day 
• Size: 2 to 3 feet tall, 9 to 29 pounds 
• Sleep: 18 to 22 hours each day to help conserve energy 
• Social life: Solitary 
• Behavior: Active at night, spends most of day eating and sleeping 
• Young: Newborn joeys live in mother’s pouch and with her until they’re around a year old 
• Conservation status: Threatened; koala’s biggest threats are loss of habitat, vehicle strikes, dog attacks, bushfires and disease 

Photo courtesy of San Diego Zoo Wildlife Alliance

How big is the San Diego Zoo’s koala colony?

Twenty-one koalas live in the San Diego Zoo. The zoo’s koala colony is the largest in the U.S. and the largest outside of Australia and China. 

What do koalas eat? 

Koalas eat around 1 to 1.5 pounds of eucalyptus leaves each day and they’re choosy about it! San Diego Zoo offers its koalas around 20 pounds of eucalyptus daily across several species so they can pick their favorite variety.  

Eucalyptus leaves don’t provide many calories, but koalas make up for this by spending most of their day sleeping.  

Video courtesy of San Diego Zoo Wildlife Alliance

Why is eucalyptus so hard to provide? 

Eucalyptus is difficult to provide because it’s naturally toxic. Most animals can’t eat it at all! Koalas are uniquely adapted to tolerate the toxins, but only in certain species of eucalyptus. Toxin levels can change seasonally and be high enough that koalas will avoid a species they’d usually eat. Of the several hundred types of eucalyptus in Australia, koalas only eat around 80. 

“Koalas will actually smell their eucalyptus before they eat it and they can tell, ‘Oh, this is safe for me to eat,’ or ‘No I should not,’” said Jennifer Moll, San Diego Zoo lead wildlife care specialist. 

Why is San Diego Zoo uniquely suited to raise koalas? 

San Diego Zoo is a great place to raise koalas because its climate mirrors Australia, which means, unlike most zoos, it can grow the koalas’ food in its backyard. While many zoos have to ship eucalyptus in, San Diego grows 35 varieties in a 10-acre farm nearby, so its koalas always have fresh, safe leaves to choose from. 

That Australian-like climate doesn’t just feed the koalas, it makes San Diego feel like a part of Australia. 

“When I went to Australia the first time, I felt like I was in San Diego,” said Nicki Boyd, San Diego Zoo general curator. “But the black birds flying around aren’t ravens or crows, they’re black cockatoos!” 

Where do the koalas live in the zoo? 

At the San Diego Zoo, the koalas live in a Queenslander-style “house” in the Australian Outback habitat. The koalas sit in tree branches about 12 feet high to simulate living up in the trees. Zoo staff use a pulley system so they can place fresh browse (eucalyptus leaves) in a canister and reel it up to reach the koalas up in the trees.  

“The Queenslander house starts with people walking on a pathway that’s supposed to mimic being on your back patio or balcony and overlooking koalas as if you were out in Australia,” Moll said. 

Photo courtesy of San Diego Zoo Wildlife Alliance

How has koala care changed over time? 

Today, the koalas live outside 24/7, but this wasn’t always the case at the zoo. 

In the 1970s and 1980s, zoos were told to keep koalas indoors most of the time. A few males were rotated outside during the day, but the females rarely went out, and every koala came back inside at night. There was some sunlight, but not enough UV. Over time, the koalas began developing metabolic bone disease.  

“We were still keeping the koalas and caring for them the same way we had been taught a couple of decades previously and didn’t realize Australia had changed their ways and found better alternatives,” Moll said. “It made us realize we need to reopen our conversations with the people we know in Australia.” 

When the new space was created in 2013, the zoo made sure all koalas lived outside 24 hours a day to combat this disease. 

“It’s definitely made a great improvement on their quality of life and quality of their health,” Moll said. 

How do koalas choose a mate? 

Female koalas at the San Diego Zoo choose their mate. The zoo has a “dating chart” or stud book that keeps track of which koalas can breed with one another to help ensure genetic diversity and a healthy population. Then, the zoo offers her first choice, but the koala may say “no thank you,” so they move down the dating chart to the next koala. 

As far as which koala makes the perfect match? Moll has a theory. 

“We’re starting to believe that female koalas are listening for the sound the male makes and also the scent he leaves behind — kind of his cologne!” Moll said. The female koala, she explains, essentially decides, “Oh yeah, that one smells good and I like the way he sounds. I’m going to go check him out.” 

Keeping genetic diversity strong is about more than the koalas in San Diego. The zoo shares what it learns with other accredited zoos — and partners in Australia — so healthy koalas here help support the future of the species everywhere. 

What’s the SAFE Koala program? 

The Koala SAFE program, Saving Animals From Extinction, is run through the Association of Zoos and Aquariums (AZA), which brings together the expertise of accredited zoos to help save koalas. Formed in June 2026 and led by the San Diego Zoo, it’s one of dozens of SAFE programs working to protect threatened species around the world.  

Koalas are what conservationists call an umbrella species: Protect them, and you protect everything living under their canopy too.  

“Koalas will be the umbrella species that can save the echidna, the wombat, the forest which would house cockatoos and many species,” Boyd said. 

Working alongside other accredited zoos, San Diego shares its research and expertise, so conservation wins reach koalas in the wild — not just those in human care. 

“We want people to see how cool and unique they are and drive empathy to help that conservation,” Boyd said. 

“We’re learning so much … we can use that knowledge and apply different strategies and send it to our colleagues in Australia,” Boyd said. 

Are koalas endangered? 

Often described as endangered, koalas are officially listed as vulnerable by the International Union for Conservation of Nature (IUCN) — a category within its broader “threatened” classification. In their home country, the Australian government has gone further, listing koalas as endangered across Queensland, New South Wales and the Australian Capital Territory. The bottom line: Koalas need our help. 

Photo courtesy of San Diego Zoo Wildlife Alliance

What are the biggest threats to koalas? 

Koalas face several threats — habitat loss, climate change and wildfires, invasive pests and disease. 

The single biggest threat is the loss of the eucalyptus forest koalas depend on. Because koalas rely almost entirely on eucalyptus for both food and shelter, anything that shrinks those forests puts them at risk. And as land is cleared for development and agriculture, koalas lose the habitat they can’t live without. 

Wildfires are destroying even more of what remains. As the climate warms, fire seasons grow more intense and eucalyptus is dangerously combustible.  

“If you’ve ever seen a eucalyptus tree burn, it’s like a candlestick. The sap is very combustible. I do worry about the future for their habitats,” Boyd said. 

The forests face a subtler danger, too. An invasive beetle that eats eucalyptus is damaging the trees in both Australia and San Diego, though Boyd is hopeful nature will find a way to keep it in check. 

“Usually there’ll be a predator that balances out the cycle for invasive pests,” Boyd said. “Hopefully, they’ll be some sort of parasitic wasp or dragonfly that decides that they’re the best thing ever.” 

Beyond their shrinking habitat, koalas also face disease, though it’s one researchers are actively fighting. Koala retrovirus, or KoRV, affects koalas in both human care and in the wild. Different strains can predispose them to other medical concerns like cancers. But there’s real progress. Australian conservationists are developing a vaccine, work San Diego Zoo hopes to support through the SAFE program. At a recent koala conference, researchers showed evidence that vaccinated koalas were doing far better than those left unvaccinated. 

How does the San Diego Zoo help koalas in the wild? 

The San Diego Zoo helps wild koalas by funding and supporting conservation work in Australia, following the lead of the researchers and organizations who know the animals and their habitats best. 

The zoo was an early supporter of the Greater Blue Mountains Koala Program and its Australian partners credit that first decade of funding with getting the research off the ground. 

San Diego’s support extends to putting its researchers in the field. On St. Bees Island off the Queensland coast, a nearly untouched koala population gave scientists a rare chance to study the animals without human interference. 

“There were only three houses on that island … so we got to watch [the koalas] without it being interrupted by the people living there, without people building and destroying the habitat,” Moll said. 

In Tandora, Queensland, the work turned to a bigger question: how to bring koalas back to places they’ve disappeared from. Researchers worked with a local farmer who once had koalas on his property and wanted them back. 

“It was a study on what does it take to repopulate an area with koalas again,” Moll said. 

And when Australia’s devastating bushfires swept through koala habitat in 2020, the San Diego Zoo’s first instinct wasn’t to rush in. It was to ask how it could help those already on the ground. 

“What we realized — they didn’t need us. That’s Australia. That’s where koalas are from … so it was more about how can we support them,” Moll said. 

It’s a philosophy that runs through all the zoo’s work abroad. The koala’s best hope lies in Australia and San Diego’s role is to help the people already fighting for them. 

Video courtesy of San Diego Zoo Wildlife Alliance

Koala fun facts 

Koalas are full of surprises, and some of the most fascinating are right at their fingertips (and toes). 

They have two thumbs. Each front paw has five digits arranged as two thumbs and three fingers, giving koalas an exceptional grip for climbing and pulling eucalyptus close. 

“They’re not opposable thumbs like ours are, but they help for grabbing that eucalyptus and bringing it down to them,” Moll said. 

They have a built-in comb. On each back foot, two toes are fused together to form a “grooming claw” the koala uses to clean its fur. 

“We call that their grooming claw because it always seems to have lots of hair stuck in it — that’s the one they’re using to help clean themselves,” Moll said. 

They’re built to climb. One toe on each back foot has no nail at all. Koalas use their powerful hind legs to push themselves up tree trunks. 

Photo courtesy of San Diego Zoo Wildlife Alliance

How can you help save koalas? 

You don’t have to be a scientist in Australia to help koalas. The simplest way to help is to support the organizations already working to protect koalas and their forests. 

• Adopt a koala. Through San Diego Zoo’s symbolic adoption program, you can help care for koalas and support conservation. 
• Visit the koalas. Seeing them in person in the Australian Outback area in San Diego, or at other AZA-accredited zoos, is one of the best ways to connect with the species. 
• Support Australian groups directly. Organizations on the ground in Australia, such as the Greater Blue Mountains Koala Program are leading the fight to save wild koalas. 

Every bit of support helps ensure that koalas, and the forests they depend on, are still here for generations to come. 

Frequently asked questions about koalas 

Are koalas bears? 

No. Despite the nickname “koala bear,” koalas are marsupials — mammals that carry their young in a pouch — not bears. 

How long do koalas live? 

Koalas typically live 10 to 15 years.  

What do koalas eat? 

Koalas almost exclusively eat eucalyptus. They eat about 1 to 1.5 pounds of eucalyptus a day, and they’re very selective about which ones they’ll munch on. 

How much do koalas sleep? 

Koalas sleep around 18 to 22 hours a day. Eucalyptus provides little energy, so koalas conserve it by sleeping most of the day. 

Photo courtesy of San Diego Zoo Wildlife Alliance

How many koalas are at the San Diego Zoo? 

The zoo is home to 21 koalas — the largest koala colony in the United States, and the largest outside Australia and China. 

Why are koalas endangered? 

Koalas are disappearing mainly because they’re losing the eucalyptus forests they rely on for food and shelter. Land clearing, wildfires, invasive pests and disease are all shrinking that habitat, leaving fewer safe places for koalas to live. 

Do koalas really have two thumbs? 

Yes, each paw has five digits arranged as two thumbs and three fingers, giving koalas a strong grip for climbing and holding eucalyptus. 

Can you see the koalas? 

Yes! You can visit the San Diego Zoo’s Australian Outback section to see their koala colony. 

All photos courtesy of San Diego Zoo Wildlife Alliance.