Nocturnal Birds and Their Sleep Patterns
Owls are well known for their nocturnal lifestyle, hunting (and hooting) throughout the night and resting out of sight during daylight hours. Other nocturnal species, including Nighthawks, Nightjars, Frogmouths and Whip-poor-wills, are also active during hours of darkness and catch up on their sleep after the sun rises.
Learn more about the typical sleeping habits of nocturnal birds and how they achieve quality rest while the rest of the world is wide awake.
There has always been an air of mystery about the lives of nocturnal birds. We may hear owls hooting at night or catch sight of a ghostly silhouette flying across a moonlit sky. However, sightings are far less common, adding to the intrigue of the ‘upside-down’ lives they lead.
Nocturnal birds are awake and active at night, foraging or hunting for food, engaging in courtship behavior, building nests and raising young under cover of darkness. During the day, they are rarely seen as they catch up on their rest, roosting in well-concealed spots tucked away deep in foliage, in a tree cavity, or camouflaged next to a tree trunk.
What Defines a Nocturnal Bird?
We know that nocturnal birds are typically active at night and rest during the day. But is there more to their behavior and lifestyle patterns than this? Read on to find out.
The fundamental difference between diurnal and nocturnal bird species is their daily awake-asleep routine. Nocturnal birds are awake during the night, and rest during the day, while the reverse is usually true for diurnal birds that sleep once darkness falls.
However, there are also several key anatomical differences and dietary variations that may also help to indicate whether a species is likely to be nocturnal or diurnal.
Nocturnal birds tend to have larger eyes and a highly developed vision. Their eyes are particularly well adapted to see in low light. Another adaptation is specialized feathers, that allow nocturnal birds to fly silently, enabling them to remain undetected while hunting.
Most nocturnal birds are carnivorous, being able to track prey that are active at night, including rodents and other small mammals. In contrast, the diet of diurnal birds is more varied, with a broader and more diverse range of feeding habits that are available and more readily found in daylight.
In nocturnal birds, the sense of hearing is particularly accurate, allowing them to track any tiny movement in their habitats without necessarily catching sight of their prey. Diurnal birds are more reliant on their eyesight, including color vision, for finding food.
Vocalizations and calls are another area in which there are differences between nocturnal and diurnal birds. Birds that are active in daylight use a wider range of songs and calls to raise alarm, to attract a mate, or to keep in contact with flock mates or family members. Hoots and screeches of nocturnal birds can be heard piercing the night sky, used as communication or to mark a territory.
A Great Horned Owl. Nocturnal birds are awake during the night, and rest during the day
Common Nocturnal Birds and Their Characteristics
Owls are perhaps the best-known example of nocturnal bird species but they are by no means the only birds that rest during the day and go about their usual business in darkness. Read on to learn more about some other nocturnal species around the world.
Owls
There are more than 200 owl species in the world, of which only the Northern Pygmy Owl and Northern Hawk Owl are not generally nocturnal. Most owls start to become active around dusk, emerging from the cavities or branches they’ve been resting on to hunt for prey.
Owls’ are known for their heart-shaped facial disks, their large eyes and their fluffy plumage, all of which are special adaptations that help them to navigate their territories in pitch darkness. Hearing and night vision are the two most important senses that help owls to successfully hunt in the dark.
An owl’s huge eyes, with enlarged corneas and lenses, account for up to 5 percent of their total body weight and contain tightly packed retinal rods that enable them to see incredibly clearly and accurately in the absence of natural or artificial light.
Nightjars
Nightjars are ground-nesting birds found in forests, grasslands and deserts. Their cryptic plumage allows them to nest unseen among leaf litter, although they may also roost among tree branches with dense foliage during the daytime.
Nightjars have excellent night vision that allows them to spot and catch flying insects which make up the bulk of their diet. Certain nightjar species, including the Common Poorwill and the Whip-poor-will, are especially vocal during the hours of darkness, and their repetitive song is usually the first (or only) sign that they are nearby.
A Northern Pygmy Owl. The Northern Pygmy Owl and Northern Hawk Owl are generally not nocturnal
A European Nightjar. Nightjars have excellent night vision that allows them to spot and catch flying insects
Kiwis
Another primarily nocturnal species is the Kiwi, native to the forests of New Zealand. Both flightless and endangered, kiwi populations have decreased in recent decades, and conservation efforts are in place to protect their habitats and eliminate predators.
Kiwis have a number of adaptations that make them well-suited for night-time activity. Their soft feathers enable them to move through their forest habitats silently, avoiding detection by potential predators. Despite having poor eyesight, Kiwis have a particularly acute sense of smell, which allows them to locate insects, worms, and fruit from the forest floor and pick them up using their long bills.
In New Zealand, the Kiwi is recognized as a keystone species, maintaining the balance and stability of the local ecosystems. They play a crucial role in seed dispersal in forests through the fruits they eat as they wander on foot, and are also important in controlling insect populations.
Kiwis also help with boosting nutrient cycling through soil aeration, piercing the ground with their needle-like bills in search of prey. All under the cover of darkness - not bad for a plump, short-sighted bird!
A Kiwi. Kiwis have a number of adaptations that make them well-suited for night-time activity
Adaptations for Nighttime Navigation and Hunting
Nocturnal birds have certain features that equip them for night-time survival. Without the visual clues that diurnal birds use for finding food and identifying nesting sites, Owls, Nightjars, and other nocturnal birds rely on other senses and adaptations to catch prey and evade predators.
Visual adaptations
The structure of the eyes of a nocturnal bird differs from those of diurnal birds, and are adapted to function well in low-light conditions.
Owls have large eyes that are tubular in shape, containing a dense concentration of photoreceptor cells called retinal rods which allow them to see even in the dimmest light. They also have a reflective layer behind their retina, which maximizes the amount of light available for vision.
Auditory adaptations
Many nocturnal birds have an acute sense of hearing, which helps them to locate any nearby prey as well as any predators that may be in the vicinity.
The Barn Owl is known for its particularly enhanced hearing, being able to catch prey with pinpoint accuracy on even the darkest moonless nights. Their flat facial disk acts as a kind of radar surface, directing even the most inaudible sounds to their ears.
Sensory adaptations
Birds that are active at night not only rely on their sense of hearing to hunt effectively but also benefit from specially adapted feathers in their plumage that allow them to fly silently through, drawing minimal attention to themselves.
This helps to avoid their prey being alerted to their presence and also from waking other birds and mammals sleeping nearby, which may end up creating a lot of unwanted noise and other activity.
Some nocturnal species, including the Kiwi, have an especially heightened sense of smell which allows them to forage for food successfully, even when they cannot clearly see the environment they are moving through.
A Barn Owl. The Barn Owl is known for its particularly enhanced hearing, being able to catch prey with pinpoint accuracy
Sleep Patterns of Nocturnal Birds
Being active at night, the sleep patterns of nocturnal birds are largely the reverse of bird species that are awake during daylight hours. But for Owls, Nightjars and Night Herons, is it just a simple case of being awake at night and sleeping all day? Read on to find out.
Remaining out of sight is the key to a good chunk of solid daytime rest for nocturnal birds. Cavities and tree hollows are favored by many owl species, as they offer additional protection from daytime predators, such as larger birds of prey.
Where hollows are not available, popular roosting spots can be found close to tree trunks, with owls taking advantage of their camouflaged plumage to blend into their surroundings unnoticed.
Nightjars have a highly cryptic plumage, which makes it hard to detect them against the leaf litter on the forest floor, even in daylight.
Diurnal birds (those that are typically active during the day), tend to sleep for longer, uninterrupted periods than nocturnal birds. Noise levels in urban environments are higher during the daytime, meaning that it is more likely that more quality rest is possible overnight rather than in daylight hours.
The presence of ambient light is a huge factor in the sleep patterns of birds, with diurnal birds sleeping for shorter periods during the summer when the sun sets later and rises earlier.
A study into the sleep of Starlings reported that on summer nights, the total duration of sleep was five hours less than in winter, and during a full moon and in areas that were well illuminated by stars, the amount of sleep was reduced by up to two hours.
A Yellow-crowned Night Heron. Remaining out of sight is the key to a good chunk of solid daytime rest for nocturnal birds
Challenges Faced by Nocturnal Birds
Sleeping when the vast majority of the world around you is awake, can pose a challenge for humans, as many night shift workers will agree. The same is true for birds, when they try to sleep during the daytime, with the presence of light, noise and risks associated with sleeping while there may be active threats or predators nearby.
For birds that naturally sleep in the daytime and hunt in darkness, the presence of light pollution can be a serious problem. Owls and other nocturnal birds are adapted to sleep in the daytime, using many techniques to minimize exposing themselves to risks.
Their camouflaged plumage allows them to blend into their woodland habitats without being noticed, and they can rest unseen next to tree trunks, or alternatively in cavities in trees.
Roosting spots are chosen out of direct sunlight, allowing them to remain still, comfortable and undisturbed all day long. Occasionally the presence of artificial light and noise pollution will cause a disturbance nearby, waking them too early. Lights that are too bright during the night, for example, from traffic, can confuse and disorient nocturnal birds.
During the day, it’s quite common for nocturnal birds to rely on a type of sleep known as Unihemispheric Slow-Wave Sleep, which allows them to shut off half of their brains while retaining a degree of awareness and vigilance of their surroundings. They can rest and benefit from the recovery from sleeping, but they are never fully unconscious and are tuned into any potential threats in their immediate environment.
Roosting in sheltered cavities or tree hollows is another way that nocturnal birds avoid predators during the day.
A Tawny Frogmouth. Roosting spots are chosen out of direct sunlight, allowing them to remain still, comfortable and undisturbed all day long
The Beauty of Nighttime Bird Calls
Birdsong is most commonly heard during the day, as males sing from perches in the upper branches of trees to attract mates and lay claim to a territory. However, some species are also well known for their nocturnal warblings. Keep reading to find out why birds may choose to sing under cover of darkness.
The eerie hooting of an owl, carrying across an empty night sky is unmistakable and typically used as a means of communication and territorial defense. The distinctive churring call of a Nightjar is possibly less familiar, although particularly soft and melodic, and is used to attract mates and claim a territory. One such Nightjar family member, the Whip-poor-will, has a distinctive and persistent call that is heard mainly at night.
Although not traditionally ‘nocturnal’, there are certain songbirds that are strongly associated with singing after dark, including the Nightingale and Northern Mockingbird. For these species, night-time tunefulness reaches a peak in the spring and summer, as males stay up late expanding their repertoires, and perfecting tuneful and complex melodies that stand out against the relative silence of the night sky.
A Northern Mockingbird. Although not traditionally ‘nocturnal’, there are certain songbirds that are strongly associated with singing after dark
Summary
More commonly heard than seen, nocturnal birds are shrouded in mystery, as we rarely catch sight of them and marvel at their ability to go about their routine activities in total darkness, including courtship, nesting, raising young, hunting and avoiding predation. Their skill at sleeping in broad daylight is impressive, and the adaptations that help them survive successfully around the clock are a source of fascination.
The threat of habitat loss is not limited to diurnal birds, and nocturnal birds are also at risk of losing their natural landscapes due to deforestation, urbanization and changes to agricultural land use.
As night hunters with specialized dietary needs, the destruction of habitats can prove a major threat to the survival of nocturnal birds. Preserving these corridors that support birds around the clock is vital to ensuring their future survival.