1. Why Emperor Penguin Parents Can Find Chicks Without Nests
In emperor penguin breeding sites, a gathering of only chicks called a "creche" forms. While parents are away at sea getting food, the chicks wait there for their return. When the parents come back, it is said that they find each other among thousands of birds [6].
Emperor penguins do not build nests, so there is no nest to use as a landmark. It is explained that parents distinguish the calls of their chicks [7]. Chicks in a creche can form groups of more than 100 birds [7]. Despite this, parents and chicks still meet.
The mechanism behind this voice identification is examined in the next section. During the creche period, chicks gather in groups that can exceed 100 individuals, and occasionally a few adults watch over them [7].
2. How Two Overlapping Sounds Work Like a Penguin's Name
The voice of an emperor penguin is made up of two overlapping sounds. When these overlap, a growling resonance is created, and this pattern serves as a clue to distinguish individuals, according to research [8].
Researchers processed recorded voices to create calls where only one of the two sounds was removed. When played back, adults and chicks responded to voices with both sounds present but did not respond to voices with one sound removed [8]. It appears that parents and chicks call out to each other using the combination of these two sounds in their voice. This is a report from one study and may not apply to all situations.
Voice recognition has also been reported in other penguin species. King penguin chicks have been reported to distinguish their parents' voices in crowds mixed with other birds [9]. Since this is a different species from the emperor penguin study, results should not be directly applied.
It is safe to accept that "experiments like this exist."
3. How Male Emperor Penguins Guard Eggs Without Eating
Each pair lays one egg. Emperor penguins do not build nests; instead, the male places the egg on his feet and incubates it. While the female goes to sea to get food for about 2 months, the male continues to warm the egg without eating anything [1].
Hatching takes between 65 and 75 days, and estimates widely used suggest the total period of fasting is about 4 months, or 115 days [2]. Another source writes approximately 120 days, showing variation depending on how it is counted [3]. It is thought they endure this using fat stored during the summer [2].
There are accounts stating that body weight decreases from an average of about 38 kg (about 84 lbs) to about 23 kg (about 51 lbs), a loss of about 40%. A loss of 15 kg is about 39% of 38 kg, which fits the description of "about 40%." Another source states 45–50%, so there is variation in the numbers [3]. What happens if the chick hatches before the female returns?
4. How Fasting Males Feed Newly Hatched Chicks "Esophageal Milk"
If the female's return is too late for the chick's hatching, it is said that the male gives the chick a curd-like substance formed from shedding esophageal tissue. This is described as being very high in fat and protein [4].
This is not the same mechanism as the "milk" produced by pigeons; it is a secretion from esophageal tissue. The period during which this can be given is said to be short, so it is reasonable to view it as a stopgap until the female returns.
When the female returns from the sea, she also feeds the chick. This is done by regurgitating food; when the chick pecks at the parent's beak, the parent releases semi-digested food [5]. Details of the regurgitation process rely heavily on secondary sources.
While only males incubate the eggs, after the chicks hatch, both parents share the care [5].
5. Why Both Parents Go to Sea While Growing Chicks Wait in the Creche
Once the chicks have grown to a certain extent, both parents begin going to sea for food. By around September, the chicks are always hungry, and it is not enough unless both parents go out to gather food together [2]. By early December, the chicks are almost the same size as their parents and grow feathers [2].
The creche is not "collective parenting" where everyone cares for all chicks. While parents are away, chicks gather in the nursery. Occasionally, a few adults watch over them [7]. At one time, there was a view that parents collectively cared for the chicks together. Later research has revised this view [7].
Parents bring food and care for their own chick. Therefore, when they return, they must find their own chick among thousands. The answer from Section 1 connects to this point.
During the creche period, chicks can form groups of more than 100, and occasionally a few adults watch over them [7].
6. What Scientists Are Still Studying About Males at Sea and Voice Recognition
Some males might be feeding in the sea at night during their fast, according to research. In winter 1998, satellite tags on four birds at Cape Washington suggested this possibility [10].
However, they did not directly see the birds eating, and the tagged birds were not necessarily breeding males. It is not yet a stage where we can say definitively that they "are eating" [10].
The number of days for fasting varies in sources: 115 days, about 120 days, and about 4 months. The amount of weight loss also varies, with accounts saying about 40% and others stating 45–50% [2][3]. There is a range in the figures due to counting methods, so this article retains that variation.
Voice recognition is also being studied in other penguins [9]. The mechanism for selecting only their own parent's or chick's voice from thousands of others still has room for further investigation.
7. A Voice-Guessing Game to Try and How to Read Original Sources
Something you can try today: Ask a family member for help. Close your eyes and have them say only "ah" from behind you, and try to guess whose voice it is. Next, have two people speak different words at the same time and test if you can distinguish who said what. When voices overlap, does it become harder to tell apart who said what? Since penguins distinguish individuals from voices where two sounds overlap, comparing this to humans helps imagine the difficulty.
For official information: The breeding flow of emperor penguins can be read on the Ministry of the Environment's page for Antarctic Penguins (available in Japanese).