A study published in Public Science Library-Comprehensive on October 12, analyzed the existing data and found that the reason for the above habit is that penguins are not able to feed two chicks, and the second egg is usually larger than the first one and is more likely to hatch

2025/05/2911:11:35 housepet 1500

text | Xu Rui

brow penguin. Image source: Lloyd Davis

Endangered brow penguin has a strange nesting habit - abandoning its first egg.

A study published in "Public Science Library - Comprehensive" on October 12, analyzed the existing data and found that the reason for the above habit is that penguins are not able to feed two chicks, and the second egg is usually larger than the first one and is more likely to be successfully hatched.

This study, conducted by Lloyd Davis and colleagues from the University of Otago, New Zealand, also describes the impact of the above findings on penguin protection.

brow penguins breed on two isolated islands southeast of New Zealand - Antipodis Islands , Bonti Islands. Therefore, compared with other species of penguins, they have the least relevant research. The only studies have shown that the number of brow penguins has dropped sharply over the past 50 years.

Davis and two colleagues investigated the islands where the brow penguins live in 1998 and observed their extremely unusual courtship and spawning habits. Since these observations remain the latest and most extensive data on brow penguins collected so far, the researchers decided to re-analyze them to provide reference for future research and conservation efforts.

brow penguins follow the countermeasures of "reducing the number of nests". Five days after the brow penguin lays its smaller first egg, the second egg will be laid, which is usually larger than the first one. Davis and colleagues found that the first egg usually disappears from the nest before or shortly after the second egg was born—and the brow penguin couple sometimes intentionally break or kick it out of the nest.

In addition, about 40% of the brow penguins will not hatch the first egg, but the second egg, and the hatching task is mainly completed by the female.

researchers suspect that this is because the brow penguin retains the two-egg reproduction strategy of its ancestors. But it will sacrifice the first egg because it will not be able to provide enough food for the two chicks.

The first egg is smaller probably because it is formed during the migration of female penguins to the island, while the second egg is formed after arriving on the island land, less restricted and therefore grows larger.

Researchers also found that the strange reproductive behavior of the brow penguin is also accompanied by amazing fluctuations in hormone levels. Analysis of penguin blood samples showed that during egg laying, female penguins had as high testosterone levels as male penguins. Female testosterone levels drop during hatching, while male testosterone levels rise, which may help males protect their nests and protect females in hatched eggs from bullying from other birds.

Davis et al. pointed out that unless the research and protection of brow penguins are increased, insufficient understanding of this species will lead to its survival being threatened.

There is evidence that climate change has negatively affected the breeding of brow penguins in the Antipodis Islands. In recent decades, more and more extreme weather has destroyed some breeding grounds and caused the death of nesting penguins.

In addition, changes in the ocean around the island have caused a sharp decline in the number of rock-hopping penguins in the eastern part of the region, which may also spread to squinting penguins.

"Such an interesting endangered penguin species is still little known today, and the best data we have is actually from 24 years ago. We urgently need more research on this extraordinary species to provide better protection," the researchers pointed out.