Tuesday, November 12, 2019

Do birds fly at night?

Many birds sleep at night, tucked away in some dense tree or bush. Likewise there are also birds that are awake and even flying around at night. There are several reasons birds fly at night. Birds fly at night for one or more of the following reasons:
  • They are nocturnal. They sleep during the day and are active at night, or
  • They are primarily diurnal but frequently forage at night, or
  • They are primarily diurnal but have been disturbed from their night time roost, or
  • They are primarily diurnal but carry on singing for courtship or to declare their territory at night, or
  • They are primarily diurnal but migrate at night

Let's discuss this in a little more detail.

Why would a bird fly at night?


You probably know that most owls are nocturnal: sleeping during the day, active at night. Most. Not all. There are some owls that are diurnal: carrying on their lives during the daylight hours and resting at night.

Owls have excellent hearing and eyesight. They can locate hidden prey items by hearing them rustle in the grass. But don't think of owls as eating only mice, though some do. Some owls eat primarily moths and other larger insects. Some owls eat wood rats, flying squirrels, and even skunks! Some owls eat earthworms, fish, salamanders, frogs, snakes, and even other smaller birds.

Photo of Western Screech-Owl sleeping in a cedar
This nocturnal Western Screech-Owl sleeps in a cedar 
during the day and flies around at night.
Photo by Greg Gillson
Owls aren't the only birds that fly at night. A group of birds called nightjars are nocturnal or crepuscular: most active at dawn and dusk. Nightjars eat moths and large insects at dusk or all through the night. They are camouflaged in mottled gray and brown plumage. They have large eyes. But like the owls, nightjars give away their presence by their voice, jarring the night with their unique calls that often serve as their names, like the Whip-poor-will.

Owls and nightjars aren't the only nocturnal birds that fly at night, though. There are some species of birds within other primarily diurnal groups that are nocturnal, or at least, active at night under certain circumstances. And, sometimes, normally diurnal birds fly at night.

Some birds that we think of as diurnal forage at night. They may hunt at night to avoid direct competition with other more aggressive species. Or they may find food that is unavailable during the daytime. For instance, at night zooplankton moves to the surface of the ocean. Lantern fishes follow. Squid follow the fish. Certain seabirds feed on these fish and squid at night.

Any bird might fly at night if its roost site is disturbed. An owl might fly into a tree, scattering the songbirds roosting there. A coyote may sneak up on the edge of a pond, causing nearby marsh birds to flee. These noisy fleeing birds may excite other birds until a whole flock is up and flying at night.

Sometimes courtship activities happen at night. There are some birds known for singing at night in the spring or, indeed, nearly year round. Many sing from a perch on the ground. Some birds may sing at night while flying overhead.

Many birds fly at night during their annual migration between nesting and wintering grounds. Not all birds that migrate do so at night, but many do. We'll discuss migration separately below.

What kind of birds fly at night?


Owls: We've discussed that many owls are nocturnal. You may be familiar with the Barn Owl, or hearing owls call at night, including Great Horned Owls, Eastern Screech-Owls, and Western Screech-Owls.

Nightjars: Eastern Whip-poor-wills and Common Poorwills are nocturnal. Common Nighthawks and Lesser Nighthawks are better though of as crepuscular.

Photo of a Killdeer on a shore line
You may hear Killdeer calling and flying day or night.
Photo by Greg Gillson
Shorebirds: The unusual American Woodcock is a crepuscular species that feeds on earthworms in Eastern forests. You may be familiar with the Killdeer at your local wetlands or ball field or shopping mall parking lots. Many people would be surprised to learn that these birds are active day and night. In fact, due to the tides rising and falling based on moon position, shorebirds forage on exposed mudflats at low tide, day or night.

Photo of a Black-crowned Night-Heron
Black-crowned Night-Herons feed at night, rest during the day.
Photo by Greg Gillson
Herons: The Black-crowned Night-Heron and the Yellow-crowned Night-Heron are two species that fly around and hunt at night. During the day they may roost in dense tangles in small groups.

Swallows: Tree and Violet-green Swallows rise several hours before sunrise to fly around "singing" and declaring their territory in the dark.

Albatrosses and petrels: Many seabirds feed on squid and other ocean animals that rise to the surface at night.

Ducks and geese: Very active at night in late winter and early spring. May fly from one pond to another several miles away if they are disturbed at their nightly roosting pond.

Photo of Northern Mockingbird singing from a tree top
Northern Mockingbirds sing through the night and through the year.
Photo by Greg Gillson
Songbirds: Some birds are well-known night singers. Two in North America that are most known for singing through the night are Northern Mockingbirds and Yellow-breasted Chats. American Robins and Hermit Thrushes are early and late singers, as well. It is believed that these night singers are lonely birds seeking a mate (okay, maybe I'm anthropomorphizing a little bit). They generally don't fly around during this singing. Rather, they tend to keep to one perch, sometimes keeping people awake who would rather be sleeping themselves.

Why do birds migrate at night?


Birds migrate between a winter home and a summer home. Migrating is dangerous and uses a lot of energy. So the rewards have to be higher than the risks of staying put. Often, birds migrate far north where there is an abundance of insect food in summer to rapidly grow and raise young. But in winter there are no insects to be found. So they may migrate back to the tropics where there are insects in winter, but more birds to compete for them.

Swallows, swifts, pelicans, loons, falcons, hawks, cranes, and hummingbirds migrate primarily during the day. Most other migrant bird species migrate at night. Why?

Migrating birds fly at various heights. Most fly between 5,000 and 20,000 feet. Small, slow-flying warblers, flycatchers, buntings and others would be easy prey for hawks during the daytime. So they fly under the cover of darkness. Flying non-stop for hours at a time is also energy-intensive and creates heat. So flying at night at higher elevations keeps birds cooler. (source)

What kind of birds migrate at night?


In the previous paragraph I listed a few birds that migrate during the day. Most other groups of birds migrate at night.

Night migrants include insect eaters such as warblers, flycatchers, vireos, tanagers.

Seed eaters migrate at night, too. These include sparrows, buntings, grosbeaks, cowbirds.

Fruit eating night-time migrants include orioles, thrushes, waxwings.

Photo of 3 Tundra Swans coming in for a landing
Tundra Swans migrate at night.
Photo by Greg Gillson
Ducks and geese migrate at night.

Some birds start migrating as soon as the sun sets. The peak of night time migration is midnight. Most birds keep flying until dawn, depending upon weather conditions.

Migrating birds are easily seen on doppler weather radar. If you are curious, check out the Birds over Portland website that features daily radar animated gifs of the previous night's migration in NW Oregon.



Many bird fly at night, for various reasons. You may hear them if you are outside at night in a quiet area. You may observe birds flying against the moon during migration. But mostly, the movement of birds at night is hidden from our view. Just know that it is happening. We have a lot to learn about the natural world.

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