Baby hummingbird appears to mimic caterpillar to avoid death

A baby hummingbird might have a special way of warding off predators, which threaten tropical hummingbird species in infancy. Baby White-necked jacobins (Florisuga mellivora) in Panama seem to pretend to be a fuzzy and dangerous caterpillar. The findings are detailed in a study published March 17 in the journal Ecology.

White-necked jacobins are a medium-sized neotropical hummingbird species primarily found in Mexico, Central America, and parts of South America. They feed on the nectar in the area’s plentiful trees and breed early in the wet seasons. In Panama, the rainy season is roughly from May through December. 

In March 2024, the team from this study spotted a White-necked jacobin nest with one female and one egg inside within Panama’s Soberanía National Park. Since this was the first of these hummingbirds that some of the team had ever spotted, they monitored the nest regularly and recruited a videographer to help document the events. 

About 18 to 20 days later, they noticed that the egg had hatched. Surprisingly, the new baby hummingbird sported long, fluffy down feathers on its back. This plumage made the tiny bird look like a dangerous caterpillar. Some caterpillar species cover themselves with stinging hairs that can cause skin reactions and inflammation, and even headaches, nausea, and fever in humans. 

Additionally, a bird called Cinereous mourner (Laniocera hypopyrra) is known for chicks that mimic toxic caterpillars. Keeping this species in mind, the team scoured the internet for photos of related humming bird species and some non-related hummingbird species to see how common these types of feathers are. Most of the other hummingbird species they looked at do not have these particular feathers, showing just how special they are. 

The team also saw that the nest appeared to be covered in seeds from local balsa trees. These seeds are also hairy-looking and help camouflage the chick and it is possible that the feathers are used more for hiding the chick and not for making predators think they are caterpillars. However, they did observe the chick moving like some of the caterpillars do when a carnivorous wasp was nearby. Since White-necked jacobins build open cup-like nests in exposed tree branches near the ground, these strategies might have evolved in this species over time. More long-term research is needed to support these hypotheses.  

According to the team, who represent the University of Colorado – Boulder, the Smithsonian Tropical Research Institute, and the National Science Foundation, tropical forests like these are full of mysteries and future discoveries. These findings show how every observation and collaboration especially might reveal something exciting. 

“We know so little about what nesting birds do in the tropics,” Jay Falk, a study co-author and postdoctoral scholar working with the University of Colorado – Boulder and the STRI, said in a statement. “But if we put more effort into observing the natural world, we might discover these kinds of behavior are very common.”

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