Several animals are commonly considered to be 'nocturnal' by nature.
Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day. The common adjective is "nocturnal".1
Some quotes from wikipedia on owls:
Most owls are nocturnal, actively hunting their prey only in darkness.2
And on Hedgehog
Hedgehogs are primarily nocturnal, although, depending on the species, they may be more or less active during the day.3
However, isn't it more likely that they simply follow a polyphasic sleep schedule?
Polyphasic sleep, a term coined by early 20th-century psychologist J.S. Szymanski, refers to the practice of sleeping multiple times in a 24-hour period—usually more than two, in contrast to biphasic sleep (twice per day) or monophasic sleep (once per day).4
It seems rare for any animals to sleep for particularly long periods of time, such as a full night. Even some house cats in a safe controlled environment will usually not sleep for more than a few hours at a time.
I find it unlikely that most animals could survive in the wild if they were truly "nocturnal". Is it possible that their classification as such is simply a result of seeing them active at night, when in fact they may sleep equally during the day?