This penguin has a unique way of molting, and they've been having some trouble lately...

Produced by: Science Popularization China

Author: Su Chengyu (popular science creator)

Producer: China Science Expo

Editor's note: In order to decode the latest mysteries of life science, the China Science Popularization Frontier Science Project has launched a series of articles called "New Knowledge of Life", which selects cutting-edge achievements in the field of life science and interprets them in plain language as soon as possible. Let us delve into the world of life and explore infinite possibilities.

Before we begin the article, we turn our attention to a sea lion from South Georgia Island.

Sea lions of South Georgia Island

(Image credit: John Eastcott)

It seems unhappy, for a simple reason: it is covered with hair that does not belong to it. This land is the territory of king penguins, and it is the molting season for king penguins. The land is covered with winter fur. The sea lion rolled in the mud and was covered with white feathers, which made it look a bit embarrassed and funny.

Not only king penguins, but all penguins will shed their fur. This is an awkward period. When king penguins shed their fur when they are young, they look like kiwi fruit with half of its skin peeled off, while yellow-eyed penguins look like they are wearing a worn-out down jacket...

Emperor Penguin Molting

(Image source: metro)

All of these penguins undergo an intensive annual molting process during which they fast and the growth of new feathers precedes the loss of old ones.

Yellow-eyed penguin molting

(Image source: Britannica)

The main reason for moulting is to keep warm and waterproof. Penguins live in cold environments, and the thermal insulation of feathers is essential for them to maintain their body temperature. Over time, old feathers gradually lose their thermal insulation and waterproofing properties. By moulting, penguins are able to renew their feathers, thereby ensuring that the new feathers have optimal thermal insulation and waterproofing properties, helping them maintain their body temperature in extremely cold environments.

There is a kind of penguin that molts a little differently, and that is the Papua penguin. During its molting process, the synthesis of new feathers precedes the shedding of old feathers. Therefore, in the early stages there will be a double layer of feathers, which become super fluffy, equivalent to wearing two layers of sweaters at once, which makes the penguin very hot.

A gentoo penguin has a double feathering (left), while another has just begun to molt (right).

(Photo credit: Agnès Lewden)

This is entirely possible because in the early stages of molting, when new feathers are growing and beginning to appear on the skin surface and the old feathers have not yet completely fallen off, the penguins are in a high metabolic state to support the rapid growth of new feathers. At this time, the double layer of feathers can better block heat, and their own metabolism produces a lot of heat. The combination of high metabolism and high thermal insulation will naturally lead to the risk of overheating.

Gentoo penguin

(Image source: wiki)

To verify this point of view, in late summer and early autumn of 2022, Agnès Lewden of the University of Brest in France came to the Aquarium in Brest and found 31 penguins for research.

Scientists used thermal imaging cameras, which detect infrared radiation emitted by surfaces and convert it into temperature data, to measure the surface temperature of different parts of the penguins every morning, including the torso, around the eyes, beak, flippers and feet.

First of all, the molting period of the Gentoo penguin is divided into 7 stages. Scientists affectionately call the "M2 stage" when they wear two layers of feathers in the early stage of molting the popcorn stage.

Gentoo penguin molting

(Image source: Reference 1)

Using thermal imaging, scientists have figured out how surface temperatures change during the molting period of Gentoo penguins. The following image uses a color scale ranging from 10°C to 32°C, with colors grading from blue (lower temperature) to yellow (higher temperature).

Thermal imaging shows changes in surface temperature during gentoo penguin molting

(Image source: Reference 1)

It can be clearly seen that the penguin in B has the lowest body surface temperature of all stages. It is in the first stage of shedding old feathers (M3), and more low-temperature colors (blue and purple) appear on the body surface, dropping from about 16 degrees Celsius to 15 degrees Celsius. This shows that the presence of double feathers increases thermal insulation, and wearing two sweaters is still very warm.

At the same time, although the penguin's trunk temperature is low, the area around the eyes is still very hot (very bright). Because the skin around the eyes is thin and rich in blood vessels, the temperature changes in this area can better reflect the penguin's core body temperature. In other words, when the core body temperature rises, the temperature of the area around the eyes will also rise accordingly.

Through software calculations, scientists calculated that at M3, the temperature of the periocular area rose from about 30°C to 32°C, and remained at a high level in the middle stage (M3 to M5). The increase in periocular temperature may be a manifestation of penguins dissipating heat through the periocular area, which is also the reason why their feet, beaks and fins emit white light in thermal images.

In the old feather stage (M1), the thermal insulation of the Gentoo penguin is poor, and the heat escapes, and the surface temperature is high at this time. Therefore, the old feathers really do not keep warm, and they must molt. As the old feathers fall off and new feathers grow, the surface temperature of the trunk gradually rises, and finally returns to the initial level when the new feathers are fully grown (M7).

In the early stages of molting, Gentoo penguins are more warm when wearing two layers of sweaters, and their body temperature rises. Fortunately, the double-layer sweater is only on the trunk, and there is less hair around the eyes, mouth, fins and feet, which are equivalent to heat dissipation outlets. The increase in temperature in these areas helps penguins dissipate excess heat in the body through radiation and convection, thereby maintaining a stable core body temperature.

Of course, Gentoo penguins have other ways of regulating their body temperature. Studies have shown that penguins regulate their body temperature by increasing peripheral blood flow during molting.

Gentoo penguin caring for chicks

(Image source: wiki)

In the context of global warming, scientists are concerned that the double coat of the Gentoo penguin may increase its risk of heat stroke, as rising ambient temperatures may cause penguins to face greater heat stress during molting, requiring more heat dissipation mechanisms to regulate body temperature.

However, organisms always have a certain ability to adapt. A 2019 study on Gentoo penguins on the Antarctic Peninsula found that these penguins have expanded their distribution range and established new breeding colonies in new ice-free habitats under the background of climate change, indicating that Gentoo penguins are able to adapt to environmental changes to a certain extent.

Another study used DNA analysis to assess the impact of past climate change on Gentoo penguin populations and found that they have historically demonstrated strong adaptability. These results can help predict the potential impact of future climate change on penguin populations.

However, as climate change intensifies further, penguins will face greater uncertainty, and protecting their habitats and food supplies remains a vital measure.

References:

1.Lewden A, Halna du Fretay T, Stier A. Changes in body surface temperature reveal the thermal challenge associated with catastrophic moult in captive gentoo penguinsJ. Journal of Experimental Biology, 2024, 227(11).

2.Kelton W. McMahon el al., "Divergent trophic responses of sympatric penguin species to historic anthropogenic exploitation and recent climate change," PNAS (2019).

3. Peña MF, Poulin E, Dantas GPM, et al. Have historical climate changes affected Gentoo penguin (Pygoscelis papua) populations in Antarctica? J. PLoS One, 2014, 9(4): e95375.

4.Tattersall, GJ, Roussel, D., Voituron, Y. and Teulier, L. (2016). Novel energy-saving strategies to multiple stressors in birds: the ultradian regulation of body temperature. Proc. R. Soc. B 283, 20161551