The hoopoe's Mohawk hairstyle is actually showing off "I stink!"?

The hoopoe (Upupa epops), one of the most widespread birds in China, is characterized by its retractable Mohawk hairdo and striking black and white wings. The hoopoe has become an Internet celebrity because of its fancy dress, but why is it so fancy?

A Hoopoe with a beautiful hairstyle | Antony Grossy / Flickr

The hoopoe makes people stay away

When it comes to beautiful feathers, our first reaction may be "for courtship", but some birds are equally beautiful in both sexes. Therefore, people have speculated on another mechanism that creates bright colors and strange appearances - perhaps the eye-catching appearance is a warning to warn predators that "I am not delicious."

Warning coloration is common in poisonous insects, but less studied in birds. Ornithologist Magdalena Ruiz-Rodíguez, who studies the hoopoe, and her colleagues designed an experiment to test whether predators would be wary of beautiful birds.

They chose four colorful birds for the experiment: blue-breasted koalas (Coracias garrulus), European bee-eaters (Merops apiaster), kingfishers (Alcedo atthis), and hoopoes. Koalas and bee-eaters often eat poisonous insects and may have toxins stored in their bodies, while kingfishers fly very fast and are difficult to catch, so they may be "unpalatable" or "not easy to eat" for predators. As for what tricks the hoopoes have, let me keep it a secret for now and listen to the following analysis.

Blue-breasted dace kingfisher | Zeynel Cebeci / Wikimedia Commons

European Bee-Eater | Pixabay

Kingfisher | Pixabay

Reis-Rodriguez and others ordered a batch of plaster models of birds, half of which were painted in the bright colors of the real birds and half in earthy brown. They then placed them in a national park in Spain that is famous for its large number of black kites (Milvus migrans).

As a result, whether it is the Buddha monk, kingfisher or bee-eater, their brightly colored models cannot scare off birds of prey. Instead, they suffered more attacks because of their eye-catchingness; while the models of hoopoes, whether brightly colored or gray, were rarely attacked. In two years, the researchers recorded a total of 111 attacks by birds of prey, only four of which were against the hoopoe models. It seems that when predators see the unique body outline of the hoopoe - the long "Mohawk" crown and the long beak, they will retreat, even without looking at the color.

A very tasty internet celebrity

So what’s so scary about the hoopoe? That’s where another study on the hoopoe, in which Reis-Rodriguez was involved, comes in.

Hoopoe is commonly known as "stinky aunt" because the female hoopoe and nest emit a foul odor during the breeding season. People compared the uropygial glands of hoopoes of different sexes and different periods - the secretions of male hoopoes and female hoopoes in the non-breeding season are white and odorless; but the secretions of female hoopoes and chicks in the breeding season are brown and have a foul odor. The odorous substance is produced by symbiotic bacteria in the gland.

But why did the hoopoe make itself smell so bad?

The caudal glands of a female (a, c) and a male (b, d) hoopoe during the breeding season. The smelly fluid hanging on the caudal gland can be seen | Martín-Vivaldi, Manuel, et al. / Journal of Avian Biology (2009)

The simplest and most crude answer is that, like skunks, the stench is used to ward off predators and protect the family.

During the breeding season, the caudal gland of the female bird will expand to 8 times its original size, and the amount of secretion will increase by 30 times. The female bird will produce smelly fluid from the beginning of egg laying to the eighth day of brooding, and even the light green eggshell will be dyed brown. It is not until the end of brooding that the secretion gradually returns to "normal". When the hoopoe chicks are frightened, they will defecate in large quantities and squeeze out a large drop of smelly fluid from the caudal gland.

In addition, hoopoes are not very hygienic, and their feces and food scraps are stored in their nests, which also adds to the stench. All this seems to indicate that the mother bird and the chicks are working together to use the stench to drive away predators.

This could also explain the hoopoe's strange appearance. To a breeding female, the foul smell combined with striking physical features (such as a mohawk) indicates that it is unpalatable; males and non-breeding females do not have a bad smell, but they share the same appearance, which can also scare off predators and gain protection.

Hoopoe feeding its chicks | João Manuel Lemos Lima / Wikimedia Commons

In addition, symbiotic bacteria produce antibiotics, so they have the function of preventing pathogens. The two functions of "fighting predators" and "fighting germs" are not contradictory, and may even complement each other. When chicks use poop to fight predators, it will definitely endanger the hygiene of the bird's nest, and the smelly liquid with antibacterial ingredients can act as a "disinfectant." In other words, if there is no smelly liquid, the little bird dare not poop so recklessly. It may also be because of the defense of pooping that the smelly liquid "disinfectant" has evolved as a compensation.

In short, the hoopoe is really a very interesting internet celebrity.

References

[1] Martín‐Vivaldi, Manuel, et al. "Seasonal, sexual and developmental differences in hoopoe Upupa epops preen gland morphology and secretions: evidence for a role of bacteria." Journal of Avian Biology 40.2 (2009): 191-205.

[2] Ruiz-Rodríguez, M., et al. "Does avian conspicuous coloration increase or reduce predation risk?." Oecologia 173.1 (2013): 83-93.

Author: Little Wombat

Editor: pee pee shrimp

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