Diurnal

What "diurnal" means

A diurnal animal is active mainly during the day and sleeps or rests at night. The behavior is called diurnality. It's the opposite of nocturnal.

Biologists sort animals into a few activity patterns:

• Diurnal: active during the day
• Nocturnal: active at night
• Crepuscular: most active at dawn and dusk
• Cathemeral: active at irregular times, day or night, like lions and fossas

Why some animals are active by day

When an animal is active depends on things like temperature, predators, and whether it finds food by sight. Daylight favors animals that rely on vision:

• Most primates are diurnal, including humans. Most monkeys and apes see in full color, a trait that's most useful in daylight.
• Most birds, including hawks, eagles and songbirds, are diurnal.
• Many reptiles are active by day because they warm up by basking in the sun.

Light is the strongest signal for an animal's internal clock, or circadian rhythm, which tells its body when to be awake.

Diurnal animals you can see at the zoo

Popular diurnal zoo animals include:

• Meerkats, which are active by day, mostly in the early morning and late afternoon, and duck into burrows to escape the afternoon heat.
• Ring-tailed lemurs, which are strictly diurnal, unlike many other lemurs.
• Gorillas and orangutans, which build fresh nests to sleep in each night. Orangutans often rest at midday and travel again in the late afternoon.
• Birds of prey such as the bald eagle.

Diurnal doesn't mean busy all day

Even day-active animals take breaks. Many are most active in the cooler morning and late afternoon and rest during the hottest part of the day, especially in summer. A diurnal animal napping at 2 p.m. is perfectly normal.

What it means for your zoo visit

• Arrive early. The first hour or two after opening is often the liveliest time of day, especially on hot days.
• Plan around the weather. On cool or overcast days, animals may stay active longer.
• Catch scheduled activities. Keeper talks, training sessions and enrichment are timed for when visitors can see animals engaged.
• Save indoor exhibits for midday. Reptile houses, aquariums and nocturnal buildings are good stops while outdoor animals rest.

Find a zoo to visit in our zoo directory.