The Role of Melatonin in Bird Sleep Cycles

As with humans, birds require a solid stretch of sleep to remain in good health. A bird’s prime physical condition enabling them to fly, forage and avoid predators, depends on getting enough quality rest each day (or, in the case of nocturnal birds, each night), as the internal physiological processes to get to work, repairing, reviving and restoring their bodily functions.

In simple terms, melatonin is a hormone that is produced in response to darkness. Associated with the regulation of sleep, melatonin also influences the wider health and behavior of birds, including controlling the timing of eggs hatching and adjusting to seasonal environmental changes.

Understanding Melatonin in Avian Sleep Cycles

A bird’s internal body clock controls the timings of the key functions it experiences on a daily or seasonal basis, including sleeping, migration, birdsong and reproduction.

Melatonin production helps to set a bird’s inner biological clock by responding to the natural, daily and seasonal changes in daylight and darkness. The changing levels of melatonin secretion offer cues that help to initiate and regulate various physiological and behavioral processes. This allows birds to synchronize their internal circadian rhythms with the natural environment.

Light exposure, melatonin production, and sleep-wake cycles interact to regulate the daily patterns of restfulness and activity of birds. Levels of light exposure control the secretion of melatonin which in turn dictates how much rest a bird will get each night.

Rest is crucial to the overall physical health and fitness of a bird on a day-to-day basis, but the benefits of synchronized circadian rhythm do not end there.

Being in tune with the timings of the natural world and their immediate environment is a significant factor in anticipating and initiating key life processes such as breeding, molting, learning, or using birdsong and migration between breeding grounds and winter territories.

A pair of Bar winged Prinia. A bird’s internal body clock controls the timings of the key functions it experiences on a daily or seasonal basis, including sleeping, migration, birdsong and reproduction

Seasonal Adjustments via Melatonin

As daylight diminishes in fall and winter, melatonin levels rise, prompting birds to adjust their daily routines. Increased melatonin cues them to start migration and prepare for the coming changes, such as molting and the reduced availability of food. Conversely, with spring's longer days, decreased melatonin production signals the time for courtship and breeding.

Daytime light regulates melatonin levels, impacting birds' sleep-wake cycles. Thus, prolonged exposure to artificial light can disrupt these natural patterns, causing health and behavioral issues. The benefits of a regulated sleep cycle extend to physical fitness, immune function, and reproductive success.

A pair of Common Cranes. With spring's longer days, decreased melatonin production signals the time for courtship and breeding

Challenges in Modern Times

Birds in the modern world face a diverse range of challenges that their predecessors didn’t encounter due to issues such as increased light pollution in urban and rural areas and habitat loss due to urban sprawl and development. Read on to learn more about the impact on birds’ sleeping patterns that the avians of today may experience.

Light Pollution

In urbanized areas, nocturnal light pollution levels from traffic and buildings can have a significant effect on melatonin production in birds at night. Melatonin production, which is inhibited by the presence of light, could be interrupted as birds may be confused into thinking that increased overnight levels may be interpreted as seasonally shorter nights.

Excessive levels of light at night can result in a range of bird behavior changes, including earlier activity in the mornings and changes to breeding patterns. Regular nocturnal activity, during the typical rest period of birds, can impact their health as they are not getting the required amount of sleep or rest needed for the necessary overnight recovery processes needed to remain in good health.

Disruption of circadian rhythms and artificial light at night can both lead to impaired cognitive function. Sleep deprivation, for example, can negatively affect memory and decision-making.

Habitat Disturbance

Disruption to habitats, including construction and deforestation, can remove vital nesting and roosting sites, which can have the knock-on effect of less quality sleep. Where roosting spots are lost, birds may necessarily settle in less suitable perches overnight and may end up not being able to get the regular quality rest they need each night.

Sleeping in sites where there is too much light exposure, for example, in areas that have been taken over by urban development, can lead to a drop in melatonin production, and may, in turn, throw a bird’s natural circadian rhythms out of sync.

In turn, this can have an impact on the timings of courtship and breeding, leaving birds in less than prime condition due to sleep deprivation and confusion over seasons and ultimately leading to a decline in bird populations.

A Wood Thrush. Disruption to habitats, including construction and deforestation, can remove vital nesting and roosting sites, which can have the knock-on effect of less quality sleep

Addressing the Melatonin Disruption

Dark skies schemes can help to minimize the use of artificial light at night, allowing birds to thrive in natural day/night conditions and benefit from more regulated melatonin production levels. Initiatives include using shielded lighting fixtures, downward-facing lights, etc.

Regulations to minimize light pollution in urban planning guidelines can help to introduce low-intensity lighting, which is less intrusive.

Conservation projects can protect habitats from excessive artificial lighting, with specialized reserves, particularly in known breeding grounds and along migration corridors, promoting natural darkness in areas or implementing bird-friendly lighting solutions.

Summary

Daily production of melatonin plays a pivotal role in the health and day-to-day behavior of birds.

As melatonin is necessary for synchronizing a bird’s circadian rhythms, a stable and uninterrupted supply is needed to ensure they remain naturally in tune with seasonal timings, including the shortening nights as winter approaches or longer days throughout the summer.

Conservation efforts to reduce light pollution and the associated disruption of a bird’s natural day-night rhythms can help to regulate a stable pattern of melatonin production. This can have far-reaching benefits not only to the immediate health of birds but also to their chances of long-term survival.