Baby hummingbird seen behaving like a poisonous caterpillar

In a rainforest in Panama, a baby hummingbird scared off a wasp by behaving like a poisonous caterpillar. That tiny bird, a white-necked jacobin (Florisuga mellivora), has given scientists the first clear record of caterpillar-style mimicry in a hummingbird.

The chick measured only about one-inch long and hatched in a cup nest not far above the forest floor. A small international team watched this single nest in Soberanía National Park in early 2024, knowing they were seeing something very unusual.

White-necked jacobin discovery

Field ***istants first noticed the nest when a female white-necked jacobin sat tightly over one egg on a low branch near a trail. 

After the egg hatched, the chick appeared as a brown, fuzzy lump that matched the dried plant fibers woven into the nest walls.

The work was led by Jay J. Falk, a National Science Foundation (NSF) postdoctoral fellow at the University of Colorado Boulder. He studies how hummingbird behavior and plumage tie into survival and biodiversity.

During repeated visits, the team saw the chick twitch its body and swing its head from side to side whenever something loomed nearby.

They later summarized the chick’s coat and movements in a study that proposed caterpillar mimicry as one way for nestlings to escape predators.

Life in a dangerous forest

For a nestling, the tropical forest around Soberanía is crowded with snakes, monkeys, birds, and hunting insects ready to eat soft chicks.

Many field biologists agree that predation is the main reason bird nests fail in these regions, especially for small open-cup nests.

Detailed research in central Panama found that some understory songbirds raise chicks from eggs in fewer than one fifth of nests.

Such low success highlights how even a small change in appearance or behavior could give young birds an edge against predators.

Hummingbirds face extra hazards because their nests are tiny, often built on exposed branches, and usually tended by a single parent.

A predator that finds such a nest can easily reach in with a beak, claw, or stinger before the chick can react or escape.

Understanding Batesian mimicry

Batesian mimicry, a survival strategy where a harmless animal copies the warning signals of a harmful one, can trick predators into backing off.

Predators that have learned or evolved to avoid the dangerous model often hesitate when they see anything with a similar look or movement.

Work on coral snakes and their mimics shows how powerful this kind of warning signal can be for prey species.

In those systems, predators often avoid harmless ringed snakes in areas with venomous coral snakes, a pattern supported by field experiments.

The white-necked jacobin hummingbird chick may benefit because predators in this forest have learned that certain caterpillars deliver painful stings and can even be lethal.

Anything that hints at those dangerous insects, whether through texture or motion, might persuade an attacker to choose a safer meal instead.

Clues from another strange chick

Years before this white-necked jacobin hummingbird observation, researchers described a cinereous mourner chick in the Amazon with bright orange down and slow head movements.

Those traits gave the nestling a strong resemblance to a hairy toxic caterpillar, an example of juvenile mimicry in a p***erine bird. 

Together, the cinereous mourner and the white-necked jacobin hint that imitating insects may be an overlooked way for young birds to stay alive.

The similarity between them also links distant forests in South and Central America through a shared problem, keeping slow-growing chicks from hungry mouths. 

Scientists noted that very little is known about how nesting birds behave in tropical regions, pointing out that closer and more frequent observation often reveals behaviors that had gone unnoticed before.

The white-necked jacobin chick’s performance joins a long list of deceptive behaviors birds use around their nests to protect their young.

One example is the broken wing display, a behavior where a parent pretends to be hurt, then runs from the nest to distract predators.

The white-necked jacobin chick, by contrast, never leaves the nest, so its only options are to hide or to look too dangerous to touch.

Mimicking a hairy caterpillar could camouflage it among nest fibers and send a warning signal to animals that have learned to avoid stings.

Scientists explained that Batesian mimicry is usually seen when one butterfly copies another, or when harmless snakes borrow the colors of venomous ones.

They added that this case stands out because it involves a bird imitating an insect, meaning a vertebrate may be copying an invertebrate.

Lessons from a white-necked jacobin

So far, scientists have doblockented this caterpillar-like behavior in only one white-necked jacobin chick, so they view it as a tentative interpretation rather than confirmed evidence.

The next step will be experiments with artificial chicks that differ in color and movement to see which versions predators attack more often.

Researchers also hope that birdwatchers and guides will report more hummingbird nests, especially in the tropics, where casual observations can still reveal major surprises.

Even a phone video of an odd-looking chick or an approaching predator can provide clues about how common behaviors like this may be. 

Findings like this one remind scientists that many survival strategies sit hidden in plain sight, waiting for someone patient enough to keep watching.

Understanding how a chick defends itself against a forest of predators may change how people view mimicry in birds and animals. 

The study is published in Ecology.

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