With their charismatic nature, signature tuxedo look, and unique mating rituals, penguins are among Earth's most beloved creatures.
The 18 species differ greatly in size, from the four-foot-tall emperor penguins, regal birds native to the rugged coastlines of Antarctica, to the little blue penguin of southern Australia and New Zealand, which grow to just 13 inches tall. (See "On World Penguin Day, Could There Be a More Adorable Bird?")
Many penguins thrive in harsh climates, such as the Adélie, which has survived in Antarctica for nearly 45,000 years. Flightless and aquatic, penguins live almost entirely in the Southern Hemipshere, where they chase after small prey with expert diving and swimming skills.
Penguins are known for their remarkable relationship habits—for instance, the birds are largely monogamous despite spending most the year apart. During mating season, males will seek out the same female every year, despite the crowds of hundreds or even thousands of other birds that live in their colony.
Unfortunately, some penguins have fallen victim to the effects of climate change. Antarctic researchers believe that climate change will reduce their nesting habitat and supply of food, particularly krill.
Warming seas and rising regional air temperatures have already caused penguin populations to plunge by as much as 50 percent in the past three decades in the West Antarctic Peninsula and Scotia Sea.
For April 25, World Penguin Day, we put together our best photographs of these gorgeous, comical birds.