Newly hatched hummingbird looks, acts like a toxic caterpillar

"Batesian mimicry" is when a species evolves to look like one that's inedible.

The white-necked jacobin (Florisuga mellivora) is a jewel-toned hummingbird found in the neotropical lowlands of South America and the Caribbean. It shimmers blue and green in the sunlight as it flits from flower to flower, a tiny spectacle of the rainforest.

Jay Falk, a National Science Foundation postdoctoral fellow at the University of Colorado, Boulder, and the Smithsonian Tropical Research Institute (STRI) in Panama, expected to find something like that when he sought this species out in Panama. What he didn’t expect was a caterpillar in the nest of one of these birds. At least it looked like a caterpillar—it was actually a hatchling with some highly unusual camouflage.

The chick was covered in long, fine feathers similar to the urticating hairs that some caterpillars are covered in. These often toxic barbed hairs deter predators, who can suffer anything from inflammation to nausea and even death if they attack. Falk realized he was witnessing mimicry only seen in one other bird species and never before in hummingbirds. It seemed that the nestlings of this species had evolved a defense: convincing predators they were poisonous.

“An exposed nest and high rates of nest predation [probably] create strong selection pressures to reduce predation, including strategies like insect mimicry,” Falk said in a study recently published in Ecology.

Now you see me…

Since they are so small and seemingly helpless, hummingbird chicks are especially tempting to predators, which is why Falk thinks that the white-necked jacobin developed such a unique defense. It’s a form of Batesian mimicry, in which a harmless species imitates warning signals from a species that is toxic or tastes terrible.

Further observation of the nest revealed that the female hummingbird had added to its hatchling’s caterpillar camouflage by lining the nest with hairy-looking material from the seeds of balsa trees. The researchers also noticed that, whenever they approached the nest to film, the chick would move its head upward and start shaking it sideways while its feathers stood on end. It was trying to make itself look threatening.

When the research team backed off, the hummingbird chick went back to laying low in its nest. They wondered whether it behaved this way with actual predators, but eventually saw a wasp known to prey on young hummingbirds creep close to the nest. The chick displayed the same behavior it had with humans, which succeeded in scaring the wasp off.

Falk determined that the feathers, color, and head-shaking were eerily similar to the larvae of moths in the Megalopygidae and Saturniidae families, which are also endemic to the region. They might not be the mirror image of a particular species, but they appear close enough that predators would consider themselves warned.

“The behavior of the white-necked jacobin, when approached by humans and a predatory wasp, resembles the sudden ‘thrashing’ or ‘jerking’ behavior exhibited by many caterpillars in response to disturbance, including in the habitat where this bird was found,” he said regarding the same study.

…now you don’t

Could there be an alternate explanation for this hummingbird cosplaying as a caterpillar? Maybe. The researchers think it’s possible that the long feathers that appear to mimic spines may have evolved as a form of crypsis, or camouflage that helps an organism blend in with its background. The balsa tree material that's similar to the feathers obviously helped with this.

It’s also possible that a form of convergent evolution occurred. Convergent evolution is the phenomenon of unrelated organisms evolving similar adaptations because of similar environmental pressures. Another explanation for the feathers in white-necked jacobin chicks is that the birds evolved spine-like feathers to protect the softest parts of their bodies from predators.

There is a chance that the long spines and feathers may play an additional role for both caterpillars and hummingbirds. In caterpillars, the spines also function as movement sensors, which may help detect approaching predators. The long feathers in young hummingbirds, as all feathers do, may help with thermoregulation.

Where could the head-shaking behavior come from? Along with the physical camouflage and protection, it is thought to be effective in startling predators such as the wasp caught on film, giving both caterpillars and hummingbird hatchlings a greater chance of survival.

The only other bird in which this mimicry has been observed is the cinereous mourner (Laniocera hypopyrra), which has chicks that hatch with spiny, bright orange feathers that are similar to the caterpillar of a Megalopygidae species it shares a habitat with. This caterpillar is so toxic that even monkeys and snakes won’t touch it. Much like the white-necked jacobin, cinereous mourner chicks also shake their heads when threatened.

Until now, hummingbirds have drawn the most attention for their iridescent plumage and flight feathers that allow for ultrafast wingbeats. Falk thinks that further investigation into the feathers of hummingbird chicks may reveal more insights into the evolution of a built-in costume.

Ecology, 2025. DOI:  10.1002/ecy.70060

Source

Hope you enjoyed this news post.

Thank you for appreciating my time and effort posting news every day for many years.

News posts... 2023: 5,800+ | 2024: 5,700+ | 2025 (till end of March): 1,357

RIP Matrix | Farewell my friend