The Sleeping Patterns of Birds: A Closer Look

Birds fall into two main categories: diurnal and nocturnal. Diurnal birds, which make up the majority, are active during the day. In contrast, nocturnal species like owls thrive at night. Regardless of their activity patterns, all birds require sleep. But how does this process work for them?

Interestingly, birds and humans share similarities in their sleep cycles. Both experience two sleep stages: slow wave sleep (SWS), a light, dreamless state, and rapid eye movement (REM) sleep, characterized by deep rest and vivid dreams. Birds spend less time in REM sleep per cycle (around 16 seconds) but may not have less REM sleep overall. Initially, scientists believed only mammals and birds exhibited these sleep traits, but recent discoveries show some reptiles also share these patterns.

Birds have developed diverse sleeping strategies to adapt to their environments. For instance, pigeons often take short naps to recharge. Meanwhile, migratory birds like sparrows significantly cut down on sleep during migration without compromising their ability to function effectively.

Why Sleep is Crucial for Birds

Sleep offers universal advantages across species. It conserves energy by reducing metabolic rates and helps animals steer clear of demanding activities. In vertebrates, sleep plays a vital role in brain growth, enhancing neural connections and improving memory [PDF].

Insufficient or irregular sleep can hinder the learning and memory formation of young birds. Artificial lighting further disrupts their rest, reducing deep REM sleep, particularly in brightly lit urban environments [PDF]. Some disoriented birds may circle artificial lights or, tragically, collide with illuminated buildings.

Sleep can enhance certain birds' capacity to recall their songs. In 2008, researchers found that young zebra finches rehearse melodies heard from adult finches during sleep. The next day, noticeable improvements in their singing were observed. They might even acquire new songs while asleep. 

Unique Sleeping Behaviors

While sleep offers clear advantages, excessive or overly deep sleep can pose risks in natural habitats.

Certain birds have modified their sleep routines to protect themselves from predators. Chinstrap penguins avoid deep sleep to remain alert and guard their chicks. Instead, they engage in extreme napping, taking nearly 10,000 “micro-naps” daily, totaling around 11 hours of rest.

Another way to handle predator threats is by sleeping with one eye literally open. Ducks and ostriches can enter a half-sleep state known as sleep-watching, keeping one eye alert to potential dangers.

Do Birds Sleep Mid-Flight?

Some bird species can partially sleep while flying. In 2016, researchers discovered that frigatebirds, a type of seabird, can sleep during flight. They may rest one or both halves of their brain while airborne, enabling them to fly nonstop during migration without needing breaks. If a frigatebird sleeps with one eye open, it’s likely to avoid collisions rather than to watch for predators.

Despite this incredible ability, frigatebirds sleep less than an hour daily during migration. How they avoid sleep deprivation remains a mystery. Recently, scientists have also observed that swifts sleep while flying. 

The common poorwill is the only bird species known to hibernate. Hibernation involves a state of controlled hypothermia, lasting weeks or even months. During this period, the bird reduces its metabolism, body temperature, and heart rate to save more energy than regular sleep allows. Its mottled feathers provide perfect camouflage in the meadows and shrublands where it hibernates.

Hummingbirds experience a similar state known as torpor, a form of temporary hibernation. While torpor typically lasts a few hours, hummingbirds can enter a deep torpor that spans the entire night, during which their body temperature may drop by approximately 20°F. For comparison, a 3°F drop in humans would cause hypothermia, requiring medical intervention. Researchers are still studying how hummingbirds manage to rewarm themselves from this deep torpor every morning.