Biologists Witness First-Ever Instance of Baby Hummingbirds Acting Like Caterpillars as a Defense

Most hummingbird babies are born naked. But one day, during the spring of 2024, when bird biologists Jay Falk and Scott Taylor, this white-necked jacobin hummingbird baby seemed to be covered in big brown feathers. They were puzzled, obviously. On the second day after the egg hatched, the two biologists visited its nest once again, as described in a report published in the journal Ecology.

All of a sudden, a predatory wasp emerged from nowhere and started pouncing upon the bird chick. Alerted by the predator hovering above its head, the hummingbird started shaking its body vigorously, also swinging and bobbing its head from side to side, just the way caterpillars do. The scene caused the biologists to become even more baffled. After extensive research, they realized that the mimicry was actually a strategy for the hummingbird to protect itself.

Birds adopt an array of different protection strategies against predators during the nesting phase, including concealment, camouflage, direct defense, distraction displays, and sometimes migration. After witnessing the abovementioned scene in Panama’s dense rainforest, they realized that one of these strategies was covering their bodies with “urticating hairs,” a type of hair found mostly on the bodies of tarantulas and caterpillars, so sharp, poisonous, and barbed that they can kill a human when touched.

Researchers called this acting behavior “insect mimicry” or “Batesian mimicry,” a rare form of mimicry in birds that they use to survive in tropical rainforests. “We found that newly hatched chicks of this species are covered in an unusual amount of long natal down feathers that look similar to Lepidoptera larvae in the area,” researchers noted. The chicks also “display a caterpillar-like disturbance behavior specifically in reaction to potential predation,” as seen in the scene of a predatory wasp. “We know so little about what nesting birds do in the tropics. But if we put more effort into observing the natural world, we might discover these kinds of behavior are very common," said Falk in a press release by the University of Colorado Boulder.

He revealed that  “The tropical rainforest is a dangerous place for small birds.” His colleagues from the Smithsonian Tropical Research Institute, who have studied birds in tropical forests, have reported that they are more likely to be eaten by predators like snakes, monkeys, insects, and even bigger birds. When Falk and his team went on a trip to the Soberanía National Park in Panama, they observed that caterpillars there also had similar hairs on their bodies that gave painful stings to predators, sometimes killing them. Some of these caterpillars also appeared to shake their heads when they felt threatened, just like the baby hummingbird did.

But it is not just the hummingbird babies who use this strategy. Researchers described that many milk snakes also employ Batesian mimicry. They cover their bodies in a pattern of red, yellow, and black coloring similar to that of venomous coral snakes as a protection strategy against predators. “A lot of these really classic examples of Batesian mimicry involve butterflies mimicking other butterflies, or snakes mimicking other snakes. But here, we have a bird potentially mimicking an insect, a vertebrate mimicking an invertebrate,” Taylor said in the press release. The study emerges like an anecdote depicting the mysterious nature of living, non-human creatures who adopt bizarre strategies to survive and feed in the wild.