Past Threats:
Penguins thrived in the Southern Hemisphere, even though they lacked flight, due in part to the absence of land-dwelling predators at their breeding grounds. This was especially true for those penguin species breeding on islands. This safety disappeared however, when humans began arriving to previously un-explored Antarctic islands and other penguins homes. Humans greatly reduced penguin populations through hunting and ill-managed research expeditions.

Hunting:
When explorer Captain James Cook reported the presence of fur seals in the Southern Ocean in 1775, it lead to a century of seal and penguin hunting. At first, seal hunters killed penguins only for use as cooking fuel, but as seal populations declined, penguin oil was produced as a substitute for seal oil. Between 1864-1866, 63,000 gallons of penguin oil were shipped from the Falkland Islands, an amount obtained from killing over 500,000 penguins. Over the next decade, penguins were harvested for oil, but harvesting eventually stopped as penguin populations became too small to make harvesting profitable. Penguin eggs were also heavily harvested, with those species living in the lower latitudes closest to human populations affected the most. The population of African penguins declined from 575,000 in 1900 to 18,000 in 1990 due to excessive egg harvesting.

Research Mishaps:
Penguins have been killed as a result of research expeditions within the Antarctic. In 1948, while conducting research on Adelie penguins, Dr. Sladen killed over 2,000 Adelie and chinstrap penguins to feed his sled dog team. As late as 1980, researchers at the Argentina Esperanza Base in Antarctica continued to feed penguins to their dogs. All sled dogs were removed from the Antarctica continent in 1990 however, and no longer pose a threat to penguins. Scientific research stations built on or near penguin colonies also upset penguin populations. For example, in 1990, an aircraft flying too low over a breeding colony in route to a base on Macquarie Island caused a stampede that resulted in the death of 1,000 adult penguins and 6,000 chicks.

Modern Threats
Penguins are threatened today by both direct and indirect human actions. Recent penguin population reductions are directly related to human actions of tourism, habitat destruction, and commercial fishing. Penguins are also harmed by secondary effects of human actions through invasive species, oil spills, and global warming.

Direct Human Actions:
Although tourism of penguin homes has the ability to raise awareness and understanding of penguins, it also causes adults to desert their nests when stressed by human intrusion. Human presence brings more harm to penguins than good, so the best way people can enjoy penguins is to visit them in captivity and view them from afar in the wild. Habitat destruction is also a significant threat to species like the African, Humboldt, Little, and Yellow-eyed penguin, whose coastal forest and desert habitats are cleared for farming or development. By developing penguin habitat for human use, penguins are brought into closer contact with humans, which has already been shown to have negative effects. On Antarctica however, most direct human interactions are minimized due to the 1991 Antarctic Environmental Protocol, which made the continent a natural reserve.

Commercial fisheries can directly harm penguins when penguins are caught in fish traps, but the greatest impact may lie in the competition of fisheries with penguins for the same fish species. Now that world fish stocks have decreased, fisheries are targeting previously unexploited species. Also, fisheries now routinely travel farther from land to fish, which places them in penguin foraging grounds. It is unknown how greatly fisheries will affect future penguin populations, but studies of the effects of krill fishery on Adelie penguins reveal that declines in breeding success and adult survival are expected as krill catch increases.

Indirect Human Actions:
Indirect human actions pose the greatest threat to penguins. Oil spills, resulting from offshore drilling or oil transportation, pose a huge threat to penguins and other marine species. In 1994, an oil spill off South Africa killed 40,000 African penguins and every year along Argentina more than 20,000 adult and 22,000 juvenile Magellanic penguins die from oil leaks in ships and pipelines. Oil destroys the insulating ability of penguin feathers, causing their body weight to drop rapidly. If penguins don't die from hypothermia, they eventually die from kidney, liver, or intestinal disease caused by inhaling and swallowing toxins while preening. The introduction of non-native species like cats, ferrets, rats, and mice to penguin habitats also has placed penguins at risk. Penguins traditionally lacked land predators, but now with few defenses against these invasive species, many penguin eggs and chicks are killed each breeding season.

Climate change is currently the largest threat to penguins. It is not know to what degree humans actions contribute to climate change, but much climate change has been linked to the rise of industrilaized human society. Penguins are very sensitive to climate and change their diets or home ranges as a result. Global warming, influenced by human pollution, has caused warming of the Antarctic Peninsula over the past 50 years. This has led to Gentoo and Chinstrap penguins extending their ranges southward. As the climate warms, it results in fewer cold winters and less sea ice. In turn, krill populations drop because young krill require sea-ice to survive the winter and grow to adulthood. A reduction in sea ice over the past 50 years may be responsible for Emperor penguin populations dropping by 50%, due to decreased adult survival. Warmer ocean temperatures caused by global warming may also cause an increase in El Niño events, which can devastate Galapagos and Humboldt penguin populations, in addition to other seabirds.

Conserving Penguins:
Human threats to penguin populations are especially grave because penguins have a low rate of reproduction due to their small clutch size and late breeding age. These factors make it difficult for penguin populations to recover quickly from large environmental and catastrophic events. Conserving penguins therefore requires reducing direct human interactions with penguins and raising awareness of the unintentional ways humans harm penguins. By reducing the use of pollutants that add to global warming and taking action to prevent oil spills and habitat destruction we can help ensure that penguins continue to delight future generations.