How the Smithsonian Zoo weighs its animals

At the Smithsonian’s National Zoo and Conservation Biology Institute, weigh-ins are a way of life.

Animals are routinely weighed by zookeepers who monitor their development and well-being. In return for having to hop, slide or slither onto a scale, the animals get a reward: a fat, juicy worm or a slice of their favorite fruit.

The Smithsonian has nearly 400 different species, and each one requires special attention. Newly born black-footed ferrets need to be weighed at least once a week to make sure they’re healthy, while mature male animals like Gunther the gray seal and Spike the Asian elephant need to pack on the pounds during breeding season. Some creatures, like the Japanese giant salamander, just need a routine checkup once or twice a year. But knowing an animal’s weight is also important if a creature suddenly needs medicine, because weight dictates the dosage.

So, how exactly do you get a salamander or a seal on a scale? Take a look:

Story continues below advertisement

Advertisement

Story continues below advertisement

Advertisement

Songbird

Getting a bird to land on a scale is hard enough — even if that dish has wiggly worms on it.

Similar in weight to:

Five sugar packets

Songbirds are neophobic — meaning they’re scared of new things, said Shelby Burns, a bird keeper at the National Zoo’s Bird House. It takes keepers a long time to acclimate these birds to strange objects like electronic scales, but enticing them with their favorite bugs for their monthly weigh-ins helps.

The red-eyed vireo, an olive-green songbird with red irises, eats insects in the spring and summer. In the fall, these birds feast on seeds and berries to give them enough energy for their long migratory flight to South America, where they winter. During breeding season, the zoo feeds them a mix of bugs and eggs, Burns said, to ensure they have enough calcium and protein to lay eggs.

Question 1 of 10

The red-eyed vireo is quite the songbird. How many songs can it sing per day?

Black-footed ferrets

With their expressive faces and compact stature, black-footed ferrets may not look like ferocious hunters. But make no mistake: These creatures are a prairie dog’s worst nightmare. A black-footed ferret’s diet is 90 percent prairie dog, and they rely on their burrows for their homes.

Similar in weight to:

A small handheld flashlight

When cattle ranchers and landowners sought to poison and kill prairie dogs, their actions made these ferrets more scarce, too. Black-footed ferrets were presumed extinct by 1980, until a small group of them was discovered on a Wyoming farm. They are still considered one of the most endangered mammals in North America.

When we visited, the Smithsonian’s National Zoo had 33 adults and 51 kits, or babies. The zoo feeds them horsemeat and rats. Live rats are given to mothers so they can teach their young how to hunt.

Question 2 of 10

Black-footed ferrets were thought to be extinct until an unlikely event led to them being rediscovered. What happened?

Fennec fox

Native to the deserts of North Africa, fennec foxes are the smallest of the canid species and don’t really hang out with humans. Getting 9-year-old Barkley to approach a keeper and then step onto a scale took training to make him less skittish, keeper Mimi Nowlin said.

Similar in weight to:

A pair of women’s shoes

Now, when keepers say the word “target,” Barkley uses his nose to tap the end of a stick. It’s a way to get him to move to a certain spot. He knows what comes next: soft bits of meat. There’s a small dead mouse, too, as a grand prize.

In the wild, fennec foxes eat insects, rodents, lizards, birds and eggs. Consuming roots, leaves and fruit helps them hydrate. As desert dwellers, they can go for long stretches without water.

Question 3 of 10

Fennec foxes have large ears that help them detect prey and ...

Story continues below advertisement

Advertisement

Story continues below advertisement

Advertisement

Red ruffed lemurs

These primates are mobile and highly curious, and their tiny, humanlike hands allow them to climb and grasp a variety of objects.

Similar in weight to:

A newborn baby

Red ruffed lemurs usually maintain a consistent weight, keeper Esther Wray said. During mating season, they may get lighter because they’re more active.

Lemurs live in a protected area on the island of Madagascar. They use their limbs to move in all kinds of ways on the forest floor and on the branches above, searching for veggies and fruit. At the zoo, their diet includes squash, green peppers, corn, sweet potatoes and carrots.

Question 4 of 10

Red ruffed lemurs eat all kinds of fruit in Madagascar. But what is their absolute favorite?

Red pandas

With so many trees and rocks to climb, getting two red pandas to step on a scale is like herding cats. Red pandas are more closely related to raccoons or skunks than giant panda bears, but they do share the same forests as pandas and also eat bamboo.

Similar in weight to:

A bowling ball

And, like pandas, they have instantly Instagram-able faces.

To get Asa and Chris-Anne to the scale, keeper Trish Jarvis has blueberries, grapes and apple slices on standby. The zoo weighs them biweekly to make sure their diet is balanced and right.

Red pandas mostly eat bamboo, which isn’t exactly high in calories. To meet their nutritional needs, the zoo also gives them biscuits and fruit.

Question 5 of 10

Where do red pandas call their home?

Japanese giant salamander

If you live in water and you’re nocturnal, a late-morning wake-up call that yanks you out of aquatic bliss can be pretty annoying.

Similar in weight to:

An average road bike

Hiro is a Japanese giant salamander out of water. Yes, he’s squirming in the plastic tub placed on an electronic scale. Yes, that rubbery, musky odor is coming from him, too. Pungent point taken, Hiro.

The National Zoo has four Japanese giant salamanders. Hiro moves among three interconnected 718-gallon tanks. Except for the occasional weigh-in or vet check, these creatures are hardly ever touched.

They are the second-largest salamander species in the world, behind the Chinese giant salamander. Their North American kin is the hellbender, found in the South and in the eastern United States. The likes of Hiro live in streams and eat fish, frogs, crabs and even the occasional rodent, Kyle Miller said. But they don’t eat that often: A slow metabolism means they can go weeks without feasting.

Question 6 of 10

How does a Japanese giant salamander breathe?

Story continues below advertisement

Advertisement

Story continues below advertisement

Advertisement

Cheetah

Cheetahs have the willowy build of a track star. Their slender frame, light skeleton and long limbs enable them to achieve speeds of 60 to 70 mph.

Similar in weight to:

A large bookcase

But it’s really their sharp turns and sudden stops that make them successful predators. They have a remarkable ability to accelerate and change direction when hunting their prey. They also have a powerful bite and suffocation technique.

In the wild, cheetahs go after small animals like rabbits, as well as young antelope, wildebeests and zebras. Yet despite its speed and maneuverability, only about half of their hunts are successful.

As of this summer, the National Zoo had 24 adult cheetahs and two youngsters, both 10 months old. The cheetahs here get weighed monthly. The Smithsonian says there are 7,500 to 10,000 cheetahs in the wild, mostly concentrated in southern Africa. However, their numbers are shrinking due to habitat loss and overhunting.

Question 7 of 10

A cheetah’s two dark tear marks give it an edge in the wild. How so?

Dama gazelle, or addra gazelle

Sahel is a shy dama gazelle. On this day, his timid nature is endearing. The 15-year-old wanders out of his stall and onto the scale as part of a weekly ritual.

Similar in weight to:

Two full-size mattresses

These gazelles are listed as critically endangered by the International Union for Conservation of Nature. Fewer than 300 remain in the wild, according to keeper Dolores Reed.

Habitat loss has pushed the dama gazelle to the fringes of the sub-Saharan desert. The shrubs and acacia trees they rely on have been cleared to make room for domesticated livestock.

They’re also threatened by overhunting and poaching. Reed says dama gazelles have ended up as bushmeat for people and armies in nations that are experiencing ongoing conflict, such as Mali, Burkina Faso, Niger and Chad. Still, Reed says there’s an effort to reintroduce the dama gazelle to Chad as part of a larger plan that also involves the oryx and addax, also part of the antelope family.

Question 8 of 10

Dama gazelles have pretty cool headgear. But what’s the technical term?

Gray seal

Getting Gunther the gray seal on a scale doesn’t just take snacks. It takes patience.

Similar in weight to:

A vending machine

“I can’t force this 600-pound seal to do anything,” keeper Sam Milne said. But she can do positive reinforcement training, a common zoo practice: Ask an animal to do something, and if they do it, they get a reward.

Gunther is a well-trained seal: He was born at the Los Angeles Zoo and has been around humans his entire life. He knows how to get on a door-size scale and stay awake for injections, blood draws and other treatments. The zoo’s five gray seals are fed herring, butterfish, capelin, mackerel and squid. They do weigh-ins once a week.

Question 9 of 10

A gray seal’s Latin name is Halichoerus grypus. What does it mean?

Story continues below advertisement

Advertisement

Story continues below advertisement

Advertisement

Elephant

At close to 13,000 pounds, Spike is one of the zoo’s biggest animals. Measuring him takes an industrial-size scale.

Similar in weight to:

A heavy-duty pickup

He’s been at the zoo since 2018, coming from Busch Gardens Tampa Bay in Florida. He is one of seven Asian elephants at the zoo, but the only male. Asian elephants are smaller than those in Africa — down to their flappy ears.

Spike is weighed weekly, and his stats are sent to the zoo’s nutrition department for any dietary tweaks. The usual fare is hay, fruits, vegetables and other nutrient-dense items.

Spike is on the heavier side now, but that’s good for a male elephant going through musth cycles when testosterone levels ... spike.

Question 10 of 10

They say an elephant never forgets. Is there any truth to this phrase?

And now, for the outtakes

About this story

Design and development by Alexis Arnold. Editing by Julie Vitkovskaya, Christian Font and Frances Moody.

Your score: 0 out of 10

ncG1vNJzZmivp6x7uK3SoaCnn6Sku7G70q1lnKedZLGkecydZK%2BZX567tbHRmpqtoaaafHN8kWxmrKWZqbW0u82imKdlqqS8bq3NoqSapF2ssqqzx61m