World Penguin Day – the globe 'must do more' to protect penguins' Antarctic habitat

Penguins – a favorite animal for many because of their clumsy, waddling gait – offer researchers a useful way to measure the health of their habitat. Christian Reiss, an Antarctic fisheries biologist at the US-based National Oceanic and Atmospheric Administration, said: "Penguins are great ambassadors for understanding the need to conserve Southern Ocean resources."

Two thirds of the world's 18 penguin species, which range from the volcanic Galapagos Islands on the equator to the frozen sea ice of Antarctica, are in decline, according to a Pew study from 2015. Antarctic penguins in particular are vulnerable to climate change as shifting ice reduces their habitat and warming seas affect their prey.

Scientists blame the decline in penguin numbers on intense fishing pressure on forage species such as krill, as well as pollution, damage to penguin breeding grounds, and climate change. Only two types of penguin – the Adélie and the King - are increasing in numbers, according to the International Union for Conservation of Nature Red List of Threatened Species.

Penguins live most of their lives at sea but return to land to breed and molt. This makes them important gauges of marine health that are easily accessible to researchers, who can then develop conservation strategies. Stanford University marine scientist Cassandra Brooks said: "Scientists need to continue working to untangle the complex interactions between climate change and penguin populations."

The Ross Sea – one of the last intact marine ecosystems in the world, home to penguins – is getting a boost. A deal sealed last year by the Conservation of Antarctic Marine Living Resources - an international group tasked with overseeing conservation and sustainable exploitation of the Antarctic Ocean - will see a massive US and New Zealand-backed marine protected area in the Ross Sea.

The largest of the 18 penguin species found today are emperors. They are around 120cm tall and weigh about 40kg, although their weight fluctuates through the year. But fossils recovered from the Antarctic peninsula reveal that a huge species of penguin which lived around 37 million years ago would have dwarfed emperors – the ancient penguins may have stood 2 meters tall and weighed up to 115kg.

Adélie penguins are one of only five species of penguins that live on the Antarctic continent, the others being the emperor, gentoo, chinstrap and macaroni penguins. Like all penguins, Adélies are excellent swimmers - some have been recorded swimming as far as 300 km (150 km each way) to forage for their chicks.