These Baby Hummingbirds Disguise Themselves as Toxic Caterpillars to Perplex Predators

PANAMA CITY — Deep in Panama’s lush forests, something unexpected unfolds that’s changing how scientists think about bird defenses. A baby white-necked jacobin hummingbird, just hatched and utterly vulnerable, doesn’t act like your typical baby bird. Instead of gaping its mouth and chirping for food when disturbed, it does something extraordinary and pretends to be something else entirely.

Scientists recently discovered that these hummingbird chicks are covered in unusually long, fuzzy down feathers and shake their heads from side to side when threatened. This bizarre behavior isn’t random; it makes them look remarkably like toxic, stinging caterpillars that many predators avoid.

Researchers from various universities and the Smithsonian Tropical Research Institute documented this fascinating behavior in a recent paper published in Ecology. Their observations point to a case of Batesian mimicry, where a harmless species evolves to look like a dangerous one. This is something rarely seen in birds.

A Baby Bird Acts Like a Caterpillar

“Some science discoveries take years. Others just take one curious observation, and having the right people in the right place,” says study author Jay Falk from the Smithsonian Tropical Research Institute and the University of Colorado, in a statement.

The discovery began when Smithsonian Tropical Research Institute researchers found a white-necked jacobin nest with a caring female and one egg on Plantation Road, a trail within Soberanía National Park in Panama. They enlisted videographer Joe See to help document events. This was the first white-necked jacobin nest the team had ever seen.

Around 18-20 days later, the researchers visited the nest accompanied by Scott Taylor, Jay’s advisor at the University of Colorado. The egg had hatched, and Taylor noticed something unusual: long, fluffy down feathers on the chick’s back that made it look strikingly similar to a caterpillar.

The chick’s appearance wasn’t the only surprise. Rather than begging for food when approached, it would rear its head upward and shake it side-to-side about once per second, while the long feathers stood on end.

This behavior proved effective in the wild. On March 12, while the mother was away, researchers observed a carnivorous paper wasp approaching the nest. The day-old chick responded with its head-shaking movement, after which the wasp, a potential predator, flew away.

A Rare Defense Strategy in the Bird World

Many caterpillars in the region have specialized hairs that can cause painful skin reactions, inflammation, and even headaches, nausea, and fever in humans when touched. By resembling these hazardous caterpillars, the hummingbird chick might be fooling potential predators into staying away.

Young animals often face extreme vulnerability to predation, especially in tropical regions. For hummingbirds, which are tiny and typically raised by a single parent, the risks are even greater. Studies have found extremely low nesting success rates in some hummingbird species, with predation being the main culprit.

When researchers compared the white-necked jacobin to other hummingbird species, they found most had little to no natal down (the feathers they are born with). Only white-necked jacobins and their close relatives, black jacobins, showed the combination of open cup nests and extensive fuzzy down that creates the caterpillar-like appearance.

Interestingly, Falk had previously discovered that approximately 20% of females in this species look like males, probably to increase access to food, and this chick’s mother was one of them. This makes the new discovery about chick appearance even more fascinating, suggesting multiple unusual adaptations within this species.

Beyond Mimicry: Other Possible Explanations

The researchers considered alternative explanations for the unusual appearance and behavior. They noticed the nest was covered with what appeared to be seeds of local Balsa trees which are also hairy-looking, making the chick well-camouflaged.

The long down feathers might help the chick blend in with the nest material. They could also serve as a physical barrier against smaller predators or help regulate temperature. However, neither of these alternatives fully explains the distinctive head-shaking behavior that so closely resembles what caterpillars do when threatened.

This is one of the few known cases of potential Batesian mimicry in birds. A comparable example is the Cinereous Mourner, a bird native to South America known for its caterpillar-like chicks that also display similar defensive movements.

Unfortunately, the researchers couldn’t continue observations after March 23rd because the chick died (though without apparent physical damage) and the female abandoned the area.

Nature’s Hidden Surprises

The white-necked jacobin’s strategy appears to have evolved independently in this genus. While many tropical hummingbirds nest under leaves or in other concealed locations, both white-necked and black jacobins build open cup nests on top of large leaves in the forest understory.

Tropical forests contain countless mysteries and discoveries waiting to be made. Nature conceals remarkable survival strategies, sometimes right in front of our eyes. In the complex life-or-death ecosystem of tropical forests, a defenseless baby bird’s best strategy might simply be to pretend to be something else entirely.