The Newly Discovered Defense Mechanism of the Jacobin Hummingbird

A chance encounter in a Panama rainforest has uncovered a new defensive behavior in white-necked jacobin hummingbird chicks. In March 2024, Michael Castaño of the Smithsonian Tropical Research Institute and Sebastian Gallan-Giraldo of the University of Antioquia in Colombia came across a hummingbird nest in Soberanía National Park. Having monitored it for a month, they were rewarded by witnessing a chick hatching and immediately noticed something unusual. Instead of emerging naked, as is the case with other hummingbirds, this one was covered with long brown feathers. What’s more, the chick started to make twitching movements, making it look like a caterpillar. The researchers published their findings recently. So why would a hummingbird chick want to do this? Let’s find out!

White-Necked Jacobin Hummingbirds

Hummingbirds are small birds native to the Americas, and they largely form the Trochilidae family of avians. There are already hundreds of known species, but new ones are discovered every year. One of their most talked about traits is their ability to fly backward, but there is still a lot that we do not know about them, especially the species that live in the more remote areas.

The white-necked jacobin hummingbird (Florisuga mellivora) is a medium-sized hummingbird between 4.3 and 4.7 inches long. Its range covers part of Mexico and south through Central America (including Panama) into Northern South America including parts of Brazil, Bolivia, and Peru. They are found in humid forest canopies and edges, often high in trees. However, they have also been spotted lower near clearings and in coffee and cacao plantations. Their diet is tree flower nectar.

Males have a dark blue head and chest but their belly and tail are white with the exception of black tips on the tail feathers. They also have a white band on the nape of their neck. Females have variable plumage but most have green upperparts and a blue-green throat.

Breeding – Protecting the Nest and Chicks

These hummingbirds are very clever about where and how they build their nests. The eggs and chicks are very vulnerable to predation by other birds, snakes, monkeys, and even insects so this clever hummingbird has a few tricks. The nests are very small and located pretty high up – some are found 10 feet off the ground. They are constructed in a shallow cup shape made from plants and cobweb materials that look exactly like their surroundings. As well as using camouflage to keep the occupants safe, the nest is positioned under a leaf that acts as a roof.

Female white-necked jacobin hummingbirds have also been seen using a special fluttering flight to distract predators.

Hatchling Hummingbirds Protecting Themselves

Despite all of the above precautions, some determined predators still make it to the nest. Therefore, the chicks themselves have developed an impressive technique through evolution. Their long brow feathers and twitching movements make them look like toxic orange caterpillars that live in the region. The researchers even witnessed a hatchling using this technique to deter a predatory wasp.

Mimicry as a Defense Mechanism

Creatures all over the world have developed a huge range of techniques and physical attributes to stop themselves from being hunted and eaten by predators. Some common examples include camouflage, playing dead, sharp spines, startling noises, and chemical features. However, mimicry is one of the most fascinating defense mechanisms you will come across.

A special type of mimicry, called Batesian mimicry, is when a non-toxic species mimics a dangerous or unpleasant species to fool predators. Batesian mimics are named after 19^th-century naturalist Henry Walter Bates. Bates conducted his pioneering research in South America  For Batesian mimicry to work you need three elements:

The model: a toxic/venomous or foul-tasting animal. In this case, the model is the native toxic orange/brown caterpillar.

The mimic: an animal that has evolved to look/act similarly to the model. In this case, it is the newly hatched chick of the white-necked jacobin hummingbird.

The predator: an animal that would prefer to avoid eating the model and therefore also avoids the mimic. In this case, it is any animal that attacks hummingbird chicks including predatory wasps.

Batesian Mimicry and Aposematism

Batesian mimicry only works because of the model’s (in this case the caterpillar’s) appearance and behavior. The caterpillar uses a type of warning signaling that comprises its color and its jerky movements. This is called aposematic signaling. After all, there is no point in being poisonous, dangerous, or foul-tasting if the predator only finds that out after it has eaten you! Ideally, you want to advertise your unpalatability in order to avoid being eaten in the first place. Batesian mimicry also relies on the predators associating the aposematic signaling with an unpleasant experience. In this case, the predator (e.g. a predatory wasp) must realize that a brown-orange color and jerky movements means something risky and damaging or at least something non-profitable.

What Affects the Success of Batesian Mimicry?

Some research has suggested that mimics are most likely to be protected by Batesian mimicry when there are many more models than mimics. So, for the hummingbirds, it would work best if there were loads more toxic caterpillars in the forest than hummingbird chicks. The theory is that if there are lots of hummingbird chicks, a small number of predators will risk it and eat them and suffer no adverse effects. This causes the aposematic signaling to stop being so effective and even the toxic caterpillars start to get eaten! However, other researchers have proposed that this increases the effectiveness of Batesian mimicry due to a feedback model. So, in this case, the caterpillar that is now getting eaten evolves to be even more toxic which in turn sometimes causes even better mimicry by the hummingbird chicks. Nature is constantly changing and evolving!

There is also evidence that the more distasteful the model, the more effective the mimicry. Finally, both the model and the predator must have occupied the area for a while so that the predator has had time to figure out what the aposematic signaling is warning them about. Having said that, there is also evidence that predators tend to generalize once they associate a particular appearance or behavior with an unpleasant outcome. Therefore, mimics can gain protection by looking like a less toxic species model if there is another model out there that is more toxic.

Which Other Animals Use Batesian Mimicry?

This type of mimicry is common in frogs, snakes, and butterflies. For example, the sanguine poison frog (Allobates zaparo) is harmless but has evolved to look like the Ecuador poison frog (Ameerega bilinguis) with its two-tone coloration. This puts off its potential bird predators.

The butterflies Papilio Memnon use Batesian mimicry to copy several other butterfly species including Pachliopta aristolochiae. The latter contains poisons that it manufactures from the plants that it eats as a larva and is therefore inedible for predators.

When it comes to snakes, the coral snake has a distinctive banding made up of red, yellow, and black. This aposematic signaling of this model lets raptors (their predators) know that the snake is venomous. It produces a neurotoxin that causes muscle weakness, breathing difficulties, and potential respiratory arrest in its victims. This includes humans if they are unlucky enough to get bitten. Scarlet kingsnakes are impressive mimics of coral snakes. They have very similar banding but the order of the bands and the color at the front of the head are slightly different. Nevertheless, it is similar enough to reduce the predation rates on scarlet kingsnakes when there are corn snakes in the same area. The scarlet snake is another corn snake mimic but does not do it quite so well!

Stand-Out Example of Batesian Mimicry

In most other examples of Batesian mimicry, the model and the mimic are the same type of animal. This means that a frog imitates another frog and a snake imitates another snake. The remarkable thing about the white-necked jacobin hummingbird chicks is that here we have a bird mimicking the larval stage of an insect and is replicating movements as well. These impressive little birds are clearly taking Batesian mimicry to the next level!