The Mystery Of The Disappearing Female Penguins

Posted on February 21st 2019

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Very close to South America’s Southern tip thousands of female Magellanic penguins seems to be vanishing from their nests. This species of penguin is native to the Patagonia region of South America and when not breeding Magellanic penguins migrate North, heading towards Uruguay and Brazil where they hunt for anchovies that live in the waters of that part of the world. Over the last ten years though conservationists have witnessed a disturbing trend, some of the migrating penguins swim far too North, often hundreds of miles away from where they breed and end up getting stuck there.

Never return home

According to a recent study, thousands of penguins fail to return following their annual migration. Some end up being stranded on the beaches of Brazil Argentina and Uruguay whilst others wash up dead with empty stomachs or worse polluted with plastic waste. What is very strange is about two-thirds of the stranded penguins are female. Scientists of course wanted to find out what was happening and why females were mainly affected.

Tagging a group of penguins

A team of researchers tagged 14 Magellanic penguins, eight males and six females with GPS monitors and then watched what they did after the end of their breeding period in 2017. After a few months of observing the group the team established a pattern. During the migrations of summer and spring, they found that males tended to stay closer to their breeding grounds in Patagonia and dived deeper. In contrast, females stayed closer to the surface of the ocean but migrated much further North than the males.

Combination of natural and man-made threats

When the female penguins arrived in the waters off the coast of Uruguay and Southern Brazil, they tended to gravitate to standing hot-spots. These sites trap the penguins most likely through a combination of strong currents that prevent the penguins from swimming back home and man-made threats such as pollution in the water that is the result of oil development and marine transportation. There are also fishery related threats such as by catch and lack of prey.

Body size is probably the main reason

Ultimately the main reason female penguins seem to be disproportionately affected might come down to something as simple as body size. The researchers say that female Magellanic penguins are smaller than their male counterparts which means it is probably harder for them to compete for food in the Southern waters which are crowded. It also means it is more difficult to fight against strong currents in the North.

The entire population is at risk

Smaller bodies also likely mean the females are probably more sensitive to ocean temperatures which means they probably seek out warmer waters in the North and avoid deep dives in the cold ocean. The study is just the first step researchers are taking towards understanding the mystery behind the penguin strandings. What is clear according to the researchers is that a decreasing number of female penguins seem to be returning to their breeding grounds each year. This means the entire Magellanic penguin population could be at risk in the not too distant future.

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