When most people think of owls, one of the facts that often comes up is that they are nocturnal. Nocturnal animals are most active during the night, sleeping by day. While most owl species are nocturnal, not all are. Adaptations found in nocturnal animals include enhanced eyesight, hearing, and sense of smell. Besides owls, other bird species known for being nocturnal include the Southern Brown Kiwi, the Kakapo, and the Common Nighthawk. Familiar nocturnal animals include bats, raccoons, and fireflies.

Diurnal animals are most active during the day, and sleep at night. For the most part, all animals first evolved to be diurnal. Nocturnal animals later evolved adaptations for being active at night in order to avoid predators and reduce competition with other species. Advanced color vision is an adaptation seen in diurnal animals. While most birds are diurnal, many species migrate at night, mostly to avoid predation. Animals known for being diurnal include most reptiles, pollinator insect species, and primates (including humans).

There are other terms to describe when animals are active:

• Crepuscular animals are most active during twilight hours, around dawn and around dusk. Examples of crepuscular birds include the Barred Owl and Chimney Swift.
    
• Cathemeral animals are active during spurts of time during the day and night. The activity is sporadic and occurs at irregular intervals. Cathermal animals are usually active during parts of both daytime and nighttime. Lions and some species of lemur are known for being cathermal.

On this date* in 1844, off the coast of Ireland, a pair of Great Auks were killed. These proved to be the last specimens of Great Auk ever collected.

The Great Auk was a flightless species. It stood up to 33 inches tall and weighed about 11 pounds. The Great Auk's scientific name, Pinguinus impennis, roughly translates to plump and flightless. The auk's black and white plumage was similar to that of penguins; penguins are so named after the auk's scientific name due to this similarity. Despite the physical similarities, the species (auks and penguins) are not closely related genetically.

Great Auks lived in the North Atlantic Ocean coasts, coming to land only for breeding. They nested colonially in areas close to favorable feeding grounds and away from predators like polar bears and White-tailed Eagles.

Although somewhat clumsy on land, Great Auks were agile in the water, able to propel itself underwater using its wings. It was also able to dive deeper and hold its breath longer than other alcid bird species.

Great Auks were once abundant. They were hunted as food by the Neanderthals more than 100,000 years ago. There are records of Great Auks being hunted more than 20,000 years ago in Spain, Italy, and France. While the Little Ice Age between the 16th and 19th centuries may have contributed somewhat to population losses for the Great Auk, it was massive human exploitation that ultimately doomed this species. Great Auks were hunted for their down and collected for their eggs, feathers, and skins.

Today there are 78 specimen Great Auks (skins) in museums and other collections. A Great Auk specimen sold to the Icelandic Museum of Natural History for £9000 in 1971; this was listed in the Guinness Book of World Records as the most expensive bird specimen ever bought and sold.

* Published sources are conflicted on the date; June 3 is also sometimes cited.