When the sun goes down, most diurnal birds retreat to rest, but the stillness of the night is often broken by unexpected vocalizations. This “chirping” is actually sustained singing or calling by birds typically heard only between dawn and dusk. While a bird’s natural circadian rhythm dictates sleep when it is dark, environmental pressures or biological drives can override this instinct, causing them to vocalize after hours. The presence of these nighttime sounds, especially in residential areas, points to a complex mix of modern human influence and deep-seated avian behaviors.
Which Birds Chirp After Dark?
The most frequent culprits for sustained nighttime singing are the Northern Mockingbird and the American Robin. The Northern Mockingbird (Mimus polyglottos) is famous for its impressive repertoire and tendency to sing continuously throughout the night, especially during the spring breeding season. This bird is a master mimic, weaving together calls and songs from dozens of other species, which can lead to the mistaken belief that multiple birds are singing. The American Robin (Turdus migratorius) is also commonly heard after sunset and before sunrise, often extending its dawn chorus into the darkness. In European settings, the European Robin (Erithacus rubecula) is the most noted nocturnal songster in urban gardens. Sometimes, the sounds are not avian at all, as the trills of insects or the croaking of frogs can be mistaken for distant bird calls.
The Impact of Artificial Light
In developed areas, the most common reason for a bird to sing at an unnatural hour is the presence of Artificial Light at Night (ALAN). Light pollution, such as that from streetlights, security lamps, or brightly lit buildings, disrupts a bird’s natural, light-regulated circadian rhythm. Birds rely on the decreasing light intensity after sunset and the increasing light before sunrise to time their activities, including the morning “dawn chorus.”
Chronic exposure to ALAN effectively tricks a bird’s system into perceiving an extended twilight period. Studies show that ALAN consistently advances the onset of singing, sometimes by an hour or more. This phenomenon is most pronounced in urban and suburban environments where light intensity remains high throughout the night.
This perceived extension of the day causes birds to begin their routine much earlier than they would in a naturally dark environment. This artificial lengthening of the active day can lead to physiological stress and reduced rest time. The effect of light pollution on the timing of vocalization is often greater than the impact of daytime noise pollution, making it a primary driver of nocturnal singing in cities.
Biological Reasons for Nighttime Vocalization
Aside from environmental disruptions, innate biological and survival factors also prompt birds to vocalize after dark. During the height of the breeding season, the drive for territorial defense and mating can override the need for sleep. Unmated male Northern Mockingbirds, for example, sing almost continuously through the night to advertise their status and attract a female.
This extended singing is a form of “sonic sparring” with neighboring males, protecting a valuable territory rich in food and shelter. The male’s large and complex song repertoire is an indicator of fitness, and singing at night maximizes the opportunity to broadcast this message when daytime distractions are minimal.
Alarm and Distress Calls
Another distinct type of nighttime vocalization is the alarm or distress call, which is a short, sharp burst of sound, unlike the sustained song. These calls are reactive, emitted in response to an immediate threat, such as a nocturnal predator like an owl or a cat. Importantly, they serve to alert other birds to the danger, allowing them to remain hidden or take evasive action.
Nocturnal Flight Calls
Finally, many species of migratory birds, particularly songbirds, vocalize while traveling high overhead during the night. These short, cryptic sounds are known as nocturnal flight calls (NFCs), which are distinct from the complex songs heard in backyards. The primary function of these calls is believed to be maintaining flock cohesion and communication as the birds navigate under the cover of darkness.