How hummingbird chicks protect themselves from being eaten

By Stephen Beech

Hummingbird chicks pretend to be a caterpillar to avoid being eaten, reveals new research.

The tiny birds, smaller than a pinky finger, act like poisonous caterpillars to survive, American ecologists say.

The unique behavior was discovered by bird biologists Jay Falk and Scott Taylor who did not know what they were looking at when they first saw the white-necked Jacobin hummingbird chick in the dense rainforest of Panama.

When they walked closer to the nest, the day-old chick, was covered in brown fuzz. began twitching and shaking its head—a behavior they had never seen in birds before.

It turns out the bird might fend off predators by mimicking a poisonous caterpillar that lives in the same region, according to the study published in the journal Ecology.

Falk, a postdoctoral fellow in Dr. Taylor’s lab at the University of Colorado, Boulder, said it was the first time such mimicry had been seen in hummingbirds.

He said: “We know so little about what nesting birds do in the tropics.

“But this could be a very common thing if we had dedicated more efforts to observe and discover new things about the natural world.”

Dr. Falk explained that white-necked jacobin hummingbirds are common in Central and South America.

Male birds have shimmering blue and green feathers, while females tend to sport low-key green plumage.

Dr. Falk, who is also a researcher at the Smithsonian Tropical Research Institute, said the rainforest is a dangerous place for small birds with snakes, monkeys, birds and even insects all preying on them.

Previous studies have suggested bird chicks in the tropics are more likely to be eaten by predators than those in temperate forests.

But the researchers may have stumbled on how the tiny hummingbird chicks survived during a trip last year to Soberanía National Park in Panama.

Despite the birds’ frequent visits to Dr. Falk’s feeders outside his research station in Panama, he had never seen a white-necked jacobin chick or its nest before.

But, last March, researchers discovered a female jacobin hummingbird incubating an egg in its nest, not far from a forest trail.

The nest, smaller than Dr. Falk’s palm, was made of plant parts to blend in perfectly with the surrounding environment.

Over the following month, the team closely monitored the nest and witnessed a chick hatch from the egg.

Unlike most hummingbirds that are born naked, the jacobin chick was covered in long brown feathers, looking nearly identical to the nest material.

The team then witnessed the chick’s unusual jerking behavior.

Scientists had never reported a similar behavior in any other hummingbird species.

Dr. Taylor said: “I started texting a video to people and asking them, ‘What does this look like?’

“And invariably, they said, ‘That looks like a caterpillar.’ It was very exciting.”

On the second day after the egg hatched, the team saw a predatory wasp approach the chick when the mother was away.

As the wasp hovered above the nest, the chick started to twitch its body vigorously like it had for the researchers, swinging its head from side to side.

A few seconds later, the wasp flew away.

The jacobin hummingbird chick reminded Dr. Falk and Prof Taylor of a paper they came across previously.

Another team of researchers reported that a young cinereous mourner, a songbird native to the Amazonian rainforest, might resemble toxic orange caterpillars from the region by having a bright orange coat and waving its head from side to side when disturbed.

Dr. Falk and his colleagues looked into other caterpillars in this region of Panama and found that many have similar-looking brown hairs that can give painful stings to predators and even kill them.

Some of the caterpillars also shake their heads when they feel threatened, much like the chick.

Scientists refer to this survival strategy of mimicking the defensive signaling of a harmful species as Batesian mimicry. For example, some non-venomous milk snakes have developed a pattern of red, yellow and black coloring similar to that of venomous coral snakes to ward off predators.

Dr. Taylor said: “A lot of these really classic examples of Batesian mimicry involve butterflies mimicking other butterflies, or snakes mimicking other snakes.

"But here, we have a bird potentially mimicking an insect, a vertebrate mimicking an invertebrate."

While the study described a single observation, the researchers hope to test their theory in the future through experiments such as placing artificial chicks with different looks and behaviors in nests to see which are more likely to be attacked by predators.

They also hope to encourage birdwatchers and citizen scientists to document more hummingbird nests.

Dr. Taylor added: “Our perception of the natural world is very biased by our own thoughts about what could be possible.

“It’s incredible what we can discover, but we really have to think broadly.”