How Do You Weigh a Hummingbird?

See Spot.

Spot is a ruby-throated hummingbird who lives at the Smithsonian’s National Zoo in Washington, D.C. But his story began just a short distance away in Virginia. Hummingbirds hatch from eggs the size of a small pea, and when Spot was just a young chick, he fell into a swimming pool and almost drowned.

Luckily, fate was on his side that day; he was scooped out of the water and rushed to a local bird rehabilitator. Due to the injuries Spot sustained from the fall, releasing him back into the wild was not an option. The rehabilitator contacted Bird House curator Sara Hallager and asked if the Zoo would be able to care for Spot. After securing the necessary permits, the team welcomed Spot into the Zoo’s collection in November 2016.

Today, Spot is 5 years old and thriving. For such a small bird, he’s got a lot of personality. Spot is a calm and curious fellow who enjoys sunning himself under the UVB lamp in his enclosure. He is also very perceptive of his keepers and likes to interact with each new item that we add to his habitat.

Curiosity is how Spot came to be scale-trained. Many of our birds participate in positive reinforcement training and voluntarily “station,” or stand still upon a scale, on a keeper’s cue. From there, we record the birds’ measurements and keep track of whether they have gained weight, lost weight or stayed the same. If needed, we can work with the Zoo’s nutritionist, Erin Kendrick, to adjust a bird’s diet to ensure they are in optimal health.

Obtaining our birds’ weights is especially important for migratory species, who appear to be hard-wired to fluctuate in weight to coincide with breeding and migration season. Ruby-throated hummingbirds like Spot breed in North America—east of the Mississippi River—in spring and summer, then fly non-stop over the Gulf of Mexico to their wintering grounds in Central America.

Obtaining voluntary weights on birds takes a lot of patience and a little help from technology. We place part of the birds’ diet on top of scales in their enclosure, then watch via camera as they land, eat their meal and fly away. Most birds just ignore the cameras, but Spot aggressively flew at the device and tried to attack it. It was clear that he did not like having a camera in his enclosure, and we had to come up with a new way to weigh him.

Thankfully, Spot is calm around keepers. Having cared for him for several years, we know that the way to his heart is through sugar water. In the wild, hummingbirds feast on tiny insects (like gnats and aphids), spiders and nectar from flowers. At the Zoo, Spot’s diet consists of a nutritionally complete nectar designed specifically for hummingbirds and other nectar-feeding birds, which we serve in a brown nectar feeder.

To differentiate his normal diet from his training reward, we serve the sugar water in a clear nectar feeder. As soon as Spot sees this special feeder, he knows he’s getting his favorite treat!

We set Spot’s sugar water feeder on a T-stand atop the scale and added a wire at just the right distance where he could sit on the perch without flapping his wings. Hummingbirds beat their wings so rapidly that they can fly forwards, backwards and hover. If you have ever seen a hummingbird feed at a flower, then you know that they hover at just the right distance so that their long tongue can lap up the nectar inside.

Encouraging Spot to land—and sit still—was crucial to getting a good reading on the scale. Now, we can get monthly weights on him. At his last weigh-in, Spot tipped the scales at 3.6 grams—1.4 grams less than a nickel!