Hummingbird Slumber: The Secret to Conserving Energy at Night

While looking out my kitchen window and watching the hummingbirds zip around my patio I wondered, if a hummingbird has a high metabolism during the day, how do they survive through the night? I did some research and decided to write a helpful post on my findings.

How do hummingbirds conserve energy at night while they sleep?

Hummingbirds enter a hibernation-like state called torpor (pronounced TOR-per), significantly reducing their metabolic rate to conserve energy at night.
During this deep sleep, they reduce their body temperature, heart rate and breathing rate to only 5% of their normal energy expenditure during the day, closely resembling death.

Due to the petite size and high metabolism of a hummingbird they have huge hurdles to overcome every night. 

Key Components to Torpor:

• Core Body Temperature Drops
  (105°F (40°C) to as low as 48°F (9°C) or lower)
• Decreased Heart Rate
  (1,250 beats per minute to as few as 50 beats per minute.)
• Reduced Breathing
  (1250 beats per minute to as few as 1-3 breaths per minute)
• Decline In Energy Expenditure
  (up to 95% lower)

In order to meet these demands successfully, hummingbirds that are in torpor slow all of their bodily functions and reflect or mirror their body temperature to the environment around them to near ambient temperatures.
While in torpor, they can look like they have stopped breathing but are still very much alive.

Common types of torpor include:

• Daily torpor – Short term torpor lasting a few hours and occurring daily. To conserve energy during periods of inactivity or reduced food availability, such as nighttime.
  Examples include hummingbirds, bats, and some mice.
• Hibernation – A prolonged form of torpor lasting weeks or months, usually during winter to survive cold temperatures and scarce food resources.
  Examples include bears and ground squirrels.
• Facultative Torpor – Torpor that occurs in response to specific environmental stressors such as cold weather or lack of food. Activated only when necessary to cope with sudden or extreme conditions.
  Examples include chickadees and lemurs.

Each type of torpor is an evolutionary adaptation to help species survive challenging environmental conditions.

The duration and season distinguish the types of torpor and how long these animals sleep.
Some experts at the National Institutes of Health (NIH) compare torpor to hibernation.

Hibernation refers to extended winter dormancy, such as bears sleeping for 6–7 months out of the year.

In contrast, hummingbirds enter a daily, temporary hibernation called torpor each night. This state of decreased metabolic activity conserves energy by reducing body functions, allowing them to survive until morning and resume their high-energy activities.

If my Jacaranda tree was heavily condensed with branches and leaves then I would have had a harder time finding this fledging. Hummingbirds camouflage during the day well and even better at night.

Ready my article:
Discovering Hummingbirds After Dark

Hummingbirds do not enter torpor only at night but have been known to enter stages of torpor when food is scarce, the weather is too cold or during heavy periods of rain.

When hummingbirds are not in torpor they generate high body heat to keep themselves warm throughout the day.

Over many generations, hummingbirds triumph over these everyday challenges.
Through environmental changes, evolutionary adaptations have become the central component in continuing the prosperous existence of hummingbird’s on this earth.

How low does a hummingbird’s body temperature drop while they are sleeping?

A hummingbird’s body temperature can drop from their normal daytime temperature of 105*F (40*C) to as low as 50*F (10*C) at night while sleeping, a state known as torpor.
In colder regions, their body temperature may drop even further, getting within a few degrees of the ambient temperature.

The reduced body temperature is reached while hummingbirds sleep in order to conserve energy overnight. Torpor allows them to reduce this demand and survive periods when food is unavailable, such as at night.

According to eBird.org, through branding practices in Wisconsin, the Rufous and Ruby-throated hummingbirds are documented surviving in temperatures of -9*F and wind chills of -36F.
See my article:
3 Reasons Why Hummingbirds Are Banded

Thermal infrared images reveal hummingbird heat distribution where one image shows a hummingbird active during the day, emitting significant body heat.
The red and yellow colors represent the location where the maximum amount of heat is produced.

While another image shows the same bird in torpor with almost no visible heat signature and almost nonexistent.
This highlights the dramatic energy-saving effects of conserving energy at night through torpor.

What is the heart rate of a hummingbird at night while in torpor?

When hummingbirds go to sleep at night their heart rate drops to approximately 50 beats per minute as compared to their normal active daytime heart rate of 1250 beats per minute.
The heart rate is so low that when in torpor a hummingbird has to “jump-start” their heart to wake up every morning.

During torpor the heart rate slows down drastically and the hummingbird can appear to look dead even though they are very much alive.
This may seem as being an impossible adaptation that occurs every night, but in actuality it is a normal response for survival.

Hummingbirds do not have to think about this adaptation, rather it happens unconsciously. 
For example, we do not notice when or how many times we breathe a day. Our body does not need to inform us to breathe, we can multi-task and perform breathing functions naturally.

This autonomic response is achieved every night for hummingbirds when they go into torpor.

This daily phenomena and everyday hurdle for hummingbirds is truly astounding and unbelievable to witness.

What is the hummingbird’s respiration rate while sleeping?

A hummingbird’s respiration rate drops drastically while in a state of torpor while they sleep, conserving energy by slowing to 1–3 breaths per minute, depending on the species and environment. This contrasts sharply with their at rest heart rate of 250 breaths per minute.

This substantial reduction aligns with their overall metabolic slowdown, conserving energy during periods of rest and reduced food availability.

A hummingbird’s heart rate while in torpor is approximately 1-3 breaths per minute.
At rest, a hummingbird breathes about 250 times per minute.
At an active in flight daytime rate it increases to 300-500 beats per minute.

Their respiratory system is designed to hold a large capacity of oxygen to sustain the required physical demands of the body.

Oxygen is inhaled through small nostrils at the end of the bill and goes into two small lungs. The lungs are connected to air sacs.
Pressure from the muscles while flying pushes air in and out of these air sacs providing fresh oxygen to the bird’s brains and muscles for proper function.

How long does it take a hummingbird to recover from torpor?

It takes a hummingbird on average between 20 min in warm weather to 1 hour in cold weather to recover from torpor. While their heart rate and breathing increases, the vibration of their wing muscles produces a “shivering” effect to generate heat.

This warming process is powered by stored fat reserves or energy derived from food consumed before entering torpor.
Hence, the importance of filling up their bellies before bed.

To generate heat, the hummingbird relies on shivering thermogenesis for torpor recovery, where its flight muscles involuntarily contract rapidly without actual movement to generate heat.

It is a physiological response to cold temperatures and is used to maintain or increase body temperature when other methods of generating heat are insufficient.

The hummingbirds’ heart rate and breathing increases as they begin to regain full control of their muscles.

Hummingbirds have been known to go into torpor while feeding and have been found hanging upside down attached to a feeder. This occurs when a hummingbird is unsuccessful in filling their reserves before sundown and has not found a safe place to perch for the night.

As important as it is for hummingbirds to feed before going into torpor it is just as imperative for them to feed right after they reverse torpor.

A hummingbird’s biological clock will automatically initiate the reverse of torpor 1-2 hours before the sun rises.
Sometimes a hummingbird can die because it cannot properly make the transition from torpor to normal daytime activity.

The first thing they do after successfully reversing the state of torpor is consume 25% of their daily intake of food. This is an evolutionary adaptation for survival.

Success Rate of Recovering from Torpor

When morning temperatures become warmer as summer approaches it is easier for hummingbirds to reverse the state of torpor.

Successful torpor recovery happens when:

• Hummingbirds have filled their energy reserves at the end of the night before entering torpor.
• The summer months are warmer.
• Not being eaten by hungry night predators while they sleep.

During the cold nights it is especially important for a hummingbird to consume and replenish their food supply prior to going into torpor. They require enough fuel to last through the night and be able to wake up successfully. The morning goal for them is to see another sun rise.

Pleasant weather eases the strain of transitioning out of torpor.

Locating a safe and secure perch for the night before going into torpor and not stranded on a hummingbird feeder will better the chances of a hummingbird surviving and minimize the risk of being consumed by cats, praying mantises or hawks.

Read my article:
10 Common Things That Kill Hummingbirds

Hummingbirds who are stronger are more likely to survive, reproduce, and pass on their traits. If you are concerned about a hummingbird’s health, contact a local animal rehabilitation center or hospital for guidance.

Final Thoughts:

Hummingbirds enter a hibernation-like state called torpor nightly, reducing body temperature, heart rate, and breathing to conserve energy. 

Each morning, they “jump-start” their heart to reverse torpor, a process taking 20 minutes to an hour, depending on weather. If they fail to feed sufficiently before bedtime in cold weather, they risk death. 

Torpor enhances survival by conserving energy, ensuring their ability to repair and rebuild (muscles and joints), and maintaining their lineage for future generations.

Happy Hummingbird Watching!