How do you get elephants to exercise, safely introduce two songbirds, or prepare cheetahs for veterinary exams? In this series, learn how animal keepers use activities, food, training, and toys to care for animals at the Smithsonian National Zoo. Learn how enrichment stimulates the senses, why training can build trust, and how breeders can come up with new ways for animals to explore and use their natural behaviors every day.

Breeders can learn a lot about the needs of animals by monitoring their weight. A heavy armadillo may need abundance (such as a puzzle feeder) to encourage it to move around. A monkey’s weight loss may mean too much competition for food, and it needs to be manually fed separately from the other monkeys in the exhibition. But how do you weigh a wobbly ferret or put an adult elephant on a scale? In this update, the breeders share their unique skills and settings for weighing animals at the Smithsonian National Zoo and Institute of Conservation Biology.

The zoo is home to five Asian elephants, but the 10-foot-tall, 40-year-old male Spike is the largest. In fact, he is the biggest animal in the zoo! So, how does the breeder weigh such a large animal? "We let him stand on the scale (politely) and reward him with his favorite food," goalkeeper Debbie Flinkman said. 

It needs a unique scale to bear the weight of an adult elephant. In this example, it is a 10-foot-long and 5-foot-wide scale made of steel plates and beams. The scale is built into the bottom of the elephant protection chute, and the breeder has trained the elephants to enter. "Opening several 10-foot high gates and several tons of hydraulic doors, we can safely weigh any of our five elephants to manage their health and welfare," Flinkman said, adding Sometimes Spike prefers to return to scale rather than enter first.

Training is especially useful for large animals that cannot be picked up and placed on the scale. At the children’s farm, the breeder helped Maggie, a 3-year-old Holstein cow, put on a halter and walk on a lead rope so that she could weigh herself weekly. They also trained her to back up when asked, which helped to ensure that all her hooves were properly placed on the scale.

"At less than 2,000 pounds, Maggie is a very big cow! Being able to work with her safely while remaining calm is the key to making the weighing process go smoothly," said goalkeeper Nikki Maticic.

Giant pandas may not be as good as elephants and Holstein cows, but they still weigh hundreds of pounds. The giant panda family is trained to enter the chute where their scale is located. "Weekly weight is easy to get because pandas often pass through this training area," said Laurie Thompson, assistant curator of pandas. Their reward for staying still while the breeder notes their weight? Honey water-favorite treat! When he was 9 months old, Xiao Qi had already learned to step on a scale and started weighing regularly.

Bird keepers must be creative to weigh everything from small hummingbirds to large Kolly bustards. Small mammal breeders teach their pair of Vondeken hornbills that the scales are not terrible. "Hornbills are easily frightened around unfamiliar objects, so we lure them to the scale with live worms," ​​said keeper Ann Gutowski. The logs placed on the scale provide a rough surface for the birds. When the birds are looking for worms, the breeder records their weight.

A small bowl of peas, corn and seeds can attract parakeets-but when five birds share an exhibition, the scale can become crowded. "In order to get everyone's accurate weight without occupying the food bowl, I am training these birds to'target' the scale at a time," said breeder Shelby Burns. The parakeet is learning to follow a goal pole—a wooden peg painted green on one end—to reach the goal. Some parakeets catch faster than others, so training sessions are tailored for each bird in the group.

It is important to weigh songbirds regularly because their weight can change rapidly. "Their fat storage and body weight fluctuate greatly during the breeding season and during spring and autumn migrations," Burns explained. Some songbirds have difficulty measuring or doubting new things. Breeders came up with clever solutions, such as disguising a weight scale or setting up a camera so that they can record weight without needing to be nearby.

The breeder also set up scales according to the natural abilities of the birds. For example, a hummingbird can hover on the scale without touching it. A perch strategically placed on the sugar water feeder keeps the hummingbird perched and still long enough to gain its weight. Take a look:

At the Smithsonian Institute of Conservation Biology, Guam Railroad Tahi is easy to weigh. "In fact, he would weigh himself," goalkeeper Erica Royer said. Tassi is the ambassador of its critically endangered species and spends a lot of time interacting with people. “Since Tasi is raised artificially by our breeder, it is easy to train him to board the scale,” Royer explained. The large terrestrial birds in the zoo, such as Kolly bustards and finches, use large scales and feel slippery on their feet. To help, the breeder puts hay on it and uses beetle larvae as bait.

"It can take months or years for birds to feel comfortable on a scale, so practice and patience are required to gain voluntary weight," Burns said. Over time, the breeder has collected a lot of data on the bird's weight, which helps the nutrition team formulate the best diet plan.

The long body and swinging nature of the black-footed ferret make it difficult to weigh. Ferrets from the Smithsonian Institute of Conservation Biology are also possible candidates for reintroduction into the wild. "They need to maintain a natural fear of humans, so we can't spend a lot of time interacting with them or training them to step on a scale," explained the breeder Vicki Lake. The long wire basket is the perfect solution for breeders to weigh ferrets quickly and safely.

In the Amazon River, guinea pigs walk into a plastic box, where they will get their favorite snack: lettuce. The breeder uses the trash can to move the small rodents to a nearby scale, then picks them up and places them on the scale to weigh them individually. "Just because I'm older than guinea pigs and can pick them up from their exhibits, doesn't mean I should do it," says breeder Cristina Castiglione. The litter box creates a familiar and safe experience for guinea pigs, so any breeder can successfully weigh them.

The lemurs in the Lemur Island exhibition are weighed once a month, and they are voluntarily placed on the scales. Breeder Walschultz said: "However, black and white lemurs have long, hairy tails. The tails are often hung on the edge of the scale, causing weight readings to fluctuate." In order to obtain more accurate weights, the breeders train lemurs. Raise the tail. After the success of the black and white collared lemurs, they also began to train ring-tailed lemurs.

Weighing can help the breeder understand whether the animal is feeling well or getting too little or too much food. Each animal has a diet designed specifically for its needs, so in order to maintain balance, the reward for stepping on the scale usually comes directly from their favorite diet. Zoo nutritionists can pair body weight with visual or hands-on inspections to monitor physical conditions and ensure that animals develop normally or maintain proper weight. If the animal needs medication, the veterinarian will use body weight to calculate the correct dose.

Breeders have developed many creative methods to measure the weight of different animals based on their knowledge of the natural history, personalities and food preferences of animals. They can get a wealth of information from a simple number and use it to help provide the best care for all the animals at the Smithsonian National Zoo and Institute of Conservation Biology.

This article was published in the National Zoo News in November 2021.

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