New research: Hummingbird chick mimics poisonous caterpillar?
ARCC Media specialist Joseph See recently accompanied researchers at the Smithsonian Tropical Research Institute to observe a rare discovery: the nest of a hummingbird known as the White-necked jacobin (Florisuga mellivora). Little did they know at the time, this special nest would unveil new scientific insights: only the second published record of caterpillar mimicry by nestling birds. You can read the full peer-reviewed publication in the journal of Ecology.
Found from Mexico to the Amazon Basin, this hummingbird is one of the most well-known hummingbirds in the Neotropics. They are big, bold, colorful, and abundant around homes and gardens. However, despite this, the nesting biology of the bird remained undescribed. In fact, for one researcher who was a specialist in this species, it was the first time in 10 years he had ever seen a nest.
The nest, a small cup of tan-colored fluff (likely constructed from the seeds of the balsa wood tree), was on top of a large leaf of a thin sapling—maybe a meter and a half off the forest floor, out in the open. We waited, and before long, a buzz of wings announced the arrival of the mother.
She had a bright blue head that contrasted with her emerald green back. Her tail flashed white in the dim forest understory. Most female hummingbirds possess an overall greenish color. However, in the White-necked jacobin, about 1/3 of female hummingbirds are nearly identical to the males in color! This is a phenomenon that researchers are still investigating, but it seems that appearing more similar to the pugnacious males may make feeding easier for these dazzling male-pattern females. This is because they are attacked less often at feeding stations than the grayish green females of the same species.
“There are many predators in the tropical rainforest that would be happy to feast on a small chick that cannot escape. Mimicry is just one of the many ways that rainforest birds have found to survive in this challenging environment. ”
We wondered if perhaps this might prove disadvantageous during nesting, when it is important for the nest and the chick to remain unnoticed. The mother alighted on the nest and began to feed the chick, inserting her sabre like bill into the chick’s tiny mouth. She settled in to brood it for a few minutes and then quietly slipped off the nest, fanning her bright tail and flying slowly across the forest floor until she was about 30 feet away, upon which she abruptly climbed into the canopy and zoomed off.
We knew the mother would be away for at least 10 minutes so we took the opportunity to carefully examine the chick. It was covered in tan fluffy hairlike feathers, that matched the nest almost perfectly. I had never seen a hummingbird chick up close, but the researchers noticed some oddities. Most hummingbirds are born nearly featherless. When the nest was disturbed the chick began twitching its head in a spasmodic manner. It looked like a fluffy caterpillar. This wasn’t normal hummingbird baby behavior. In fact, this is similar behavior to a few caterpillars in the rainforest that deliver a poisonous sting. Could this, in fact be mimicry? After taking some measurements we had backed away from the nest when a small wasp showed up. Wasps have been recorded attacking baby birds. As it hovered over the nest, the chick began to flick its head to and fro again. The wasp flew away.
This isn’t the first time a baby bird in the rainforest has been proposed to mimic a caterpillar. Chicks of the otherwise unremarkable looking cinereous mourner—who’s sad song is one of the characteristic morning sounds of the Amazon rainforest resemble bright orange flannel moth caterpillars. Flannel caterpillars look like Trump’s hairpiece has gone for a walk in the jungle, and deliver one of the most excruciating stings of any insect. And just like the baby jacobin, the cinereous mourner chick twitches like a caterpillar when disturbed.
For many tropical rainforest birds studied, nest predation is a serious issue, with nest mortality rates being much higher than other studied species in temperate forests. There are many predators in the tropical rainforest that would be happy to feast on a small chick that cannot escape. Mimicry is just one of the many ways that rainforest birds have found to survive in this challenging environment.
As we left, we were eager to continue to monitor this hummingbird family. There were still many unknowns about the life history of this common hummingbird. No one had documented, for example, how long it would take for the baby to fledge. Unfortunately, about 2 weeks later disaster struck. When researchers arrived, they found the chick dead in the nest, the mother nowhere to be seen. That morning there had been a heavy downpour that perhaps caused the chicks demise.
While we were unable to tell the full life story of the White-necked jacobin, this observation demonstrates that so much about our natural world remains to be discovered. Knowing about each species life history not only helps us understand more about what each species needs to survive, but it gives us a deeper appreciation of the wonderful diversity of life on our planet.
