For World Penguin Day, we"re featuring a jaunty group of southern rockhopper penguins on a Falkland Islands beach. Most penguins slide over ice on their bellies, but these small penguins opt for more aerobic locomotion—they hop. Of all penguin species, rockhoppers are among the most numerous. But pollution, overfishing, and climate change have taken a toll: Their population has declined by about 30% over the last 30 years. Today, there"s an estimated 1.5 million breeding pairs of rockhoppers. About 1 million of those are southern rockhopper couples, like these, with the northern and eastern subspecies accounting for the rest.