Diurnal and Nocturnal Birds
Most birds are diurnal, which means they are most active during the day but they typically rest at night. Nocturnal birds, such as owls, frogmouths, nighthawks, and night-herons, on the other hand, are most active during the night. They forage, hunt, care for their young, preen, and do other activities necessary for survival in the darkest night hours. Passerines, waterfowl, shorebirds, gulls, and most raptors are all diurnal birds, but when they’re not being active, what do they do?
How Birds Sleep
Like other animals that are active during the day, the principle nighttime activity of birds is sleeping. Birds choose how they sleep very carefully to ensure they can survive through the night, and they have certain tricks that help give them warning about predators or to protect them from the elements.
Many bird species choose cavities or niches to roost in at night, which prevents predators from having easy access to them. These same cavities also provide shelter from poor weather and may include bird roost boxes or empty birdhouses. Snags, dense thickets, and tree canopies are other common roosting spots. Wading birds such as herons, egrets, and flamingos will sleep standing in water or on an island. The splashing sounds and wave vibrations of a predator coming toward them through the water acts as an instant warning system in case of danger. Ducks, geese, and other waterfowl will float on the water to sleep, which gives them the same noise alarm system that wading birds take advantage of. These birds also often float in large flocks while they sleep, giving them a better advantage of numbers in case a predator approaches. Small birds sleep perched high in trees, typically close to the trunk of the tree. The trunk holds heat from the daytime to provide better shelter, and the birds will be alerted to any vibrations or noises predators make if they climb the tree looking for prey. Many birds, such as red-winged blackbirds and other gregarious species, form large roost flocks at night. This provides them safety in numbers as they sleep. Several birds on the edges of the flock may remain alert through the night to guard against predators or other threats as well.
Sleeping on Cold Nights
Very cold winter nights present extra challenges for birds at night. When temperatures drop, a sleeping bird could be subject to hypothermia, frostbite, and other dangerous conditions, but birds have adapted to sleep well even on the coldest nights.
Many bird species, most notably hummingbirds, can enter a state of torpor when they sleep. This lowers their body temperature, slows their metabolism, and conserves energy for them to survive colder temperatures at night. Birds that gather in large roosts or join together in cavities or roost boxes can share body heat as they sleep. This can be risky, however, and birds may smother if they are grouped too closely in a small area with little ventilation. Birds tuck their bills into their shoulder or backs while sleeping. This puts their nares (nostrils) into their plumage where the air is heated by their bodies, giving them warmer air to breathe while they sleep. Birds have other methods to keep warm, and on cold nights they will fluff their feathers to create better air pockets to insulate themselves from low temperatures. Parent birds will cover their chicks at night to keep them safe and warm no matter what the weather conditions.
No matter where birds sleep or what the weather may be, they always take steps to ensure they survive to see another day of activity.
Other Bird Nighttime Activities
While sleeping is the most popular nighttime activity for most birds, it is not the only thing birds will do at night. Depending on the time of year, birds may also work to attract mates or migrate to a new part of their range at night.
Night Singing: Birds that sing at night are advertising their territory at a time when there is less ambient noise and their calls can be heard at greater distances. This can help deter competitors as well as attract a mate. Many birds, such as the northern mockingbird, sedge warbler, and whip-poor-will have been known to sing nearly through the entire night. Nights with bright moonlight or in areas where there is a lot of artificial light are often filled with birdsong. Night Migration: Many diurnal birds disrupt their activity patterns in order to migrate during the night instead of during the day. This allows them to take advantage of the same routes that birds of prey will use. Since raptors need daytime thermal currents to soar, migrating at night helps smaller birds avoid contact with too many airborne predators. Birds also use stars for navigating, and the less turbulent air at night can make flight easier and more efficient.
While daytime may be the best time to see most birds, understanding where birds go at night can help birders better appreciate how birds survive and take steps to help even the smallest birds survive every night.
