It doesn’t take a degree in ornithology to recognize that hummingbirds are unique. From their tiny bodies to their iridescent feathers, almost everything about the winged gems is distinctive. But beyond the gravity-defying acrobatics and perpetual pollination, there is a lesser-known hummingbird behavior that is almost unheard of in the avian world: peeing.
In fact, the winged gems urinate all the time, says Anusha Shankar, a biologist at the Tata Institute of Fundamental Research in Hyderabad, India. She would know: As the self-described “hummingbird pee person,” Shankar’s professional bona fides include being peed on by countless hummers and collecting their urine to study their metabolism.
It may seem surprising that this is possible—after all, the vast majority of birds don’t pee in a stream like mammals, instead releasing all of their watery waste with their poop. How and why did hummingbirds develop such a different behavior?
A Tricky Balance
As with so many animal adaptations, it all begins with water. Since drinkable water is often a fickle resource in nature, most birds constantly contend with the threat of dehydration, which could prove fatal. Accordingly, they have evolved to obtain most of their water from their food and cut down on losses wherever possible.
One of the most critical mechanisms protecting birds from dehydration involves how they remove waste from the body. To dispose of unwanted metabolic byproducts, almost all birds convert unneeded nitrogen—a major component in the urine of humans and other animals that excrete liquids—into crystals of uric acid. While this process is energetically costly, it offers a distinct advantage: Unlike other forms of nitrogen waste disposal, uric acid can be expelled with a bird’s poop without wasting any water. This chemical is what gives bird droppings their characteristic whitish color.
The uric-acid system works perfectly for birds that eat everything from meat to insects to seeds. But hummingbirds have very different dietary requirements. To power their turbocharged lives, hummers need to consume more energy per gram of body mass than any other vertebrate, Shankar says. That’s why they have evolved to constantly drink nectar, the syrupy liquid produced by plants to entice pollinators. With its high sugar concentration, nectar is ideal hummingbird fuel.
If a hummer retained all of the water that it drank as nectar, it would quickly put on too much weight to fly.
However, the sugar-water diet presents its own challenges. “A hummingbird’s main goal during the day is to maintain a proper body weight,” Shankar says. If a hummer retained all of the water that it drank as nectar, it would quickly put on too much weight to fly. “If you can’t pee, what are you going to do with all of that water?”
To maintain this tricky balance, hummingbirds have developed a host of features to adapt. With a diet of easy-to-digest foods like sugar and spiders, hummers have reduced their digestive tracts to the bare minimum. “Birds mostly have simple guts, but hummingbird guts are just tubes going straight through their bodies,” Shankar says.
But don’t confuse this simplicity for a lack of functionality: Studies have found that hummingbird guts are incredibly efficient at extracting energy from nectar, leaving pee almost entirely sugar-free. (“I’ve been tempted to taste it,” Shankar confesses, but she ultimately deferred to more precise methods.) This is made possible due to the birds’ specialized kidneys, which can strip water from their blood and pump out pee faster than you can say “Amethyst-throated Mountain-Gem.” From beak to cloaca, Shankar estimates that it takes hummers only about an hour to process a meal.
From beak to cloaca, Shankar estimates that it takes hummers only about an hour to process a meal.
After leaving the kidneys, all that’s left is highly diluted urine containing trace amounts of excess salts and sugars. And the nitrogen waste that other birds so cleverly convert into water-saving uric acid? That’s in a hummingbird’s pee, too—but mostly in the form of ammonia. Because ammonia can be toxic and requires a lot of water to remove, animals that pee out the chemical tend to be aquatic. Thanks to their perpetual overhydration, though, hummingbirds and other nectar-drinking species are more than happy to spare some extra liquid to flush the substance.
If you spend enough time watching hummers at a feeder or a patch of native flowers, you might be able to catch them in the act of peeing. Of course, you would be forgiven for focusing more closely on their gorgeous gorgets and whistling wingbeats. But even if hummingbird pee is more splashy than flashy, it’s yet another remarkable behavior by a family of birds that never ceases to amaze.
