Hummingbirds are known for their incredibly fast heartbeat and metabolism. Their tiny hearts can beat up to an astonishing 1,260 times per minute while at rest. This rapid heartbeat allows hummingbirds to meet their high energy needs and is an adaptation that enables their unique hovering flight.
Why do hummingbirds have such fast heart rates?
Hummingbirds have the fastest heart rate of any animal on Earth. There are several key reasons why their hearts beat so quickly:
- High metabolism – Hummingbirds have very high metabolic rates. Their metabolism is approximately 10 times faster than an elephant’s. This fast metabolism requires a lot of oxygen and energy, necessitating a rapid heart rate.
- Small heart size – A hummingbird’s heart is very small, averaging only about 0.2% of their total body weight. This smaller organ must beat faster to pump adequate blood and oxygen throughout their body.
- Hovering flight – To hover in midair while drinking nectar from flowers requires a huge amount of energy. Their heart has to beat fast enough to meet these intense energy demands.
- Temperature regulation – Hummingbirds have high body temperatures, averaging 105°F. Their rapid heart rate helps circulate blood to their skin to release excess heat.
By beating over 50 times per second while at rest, a hummingbird’s heart is able to properly supply its tissues with oxygen and energy. During flight, their heartbeat can reach as high as 1,260 beats per minute!
Average hummingbird heart rate at rest
When a hummingbird is perched and at rest, its heart rate slows down significantly from its active, in-flight pace. But their resting heart rate is still incredibly fast compared to other animals.
The average hummingbird heart rate while perching is:
- 225 beats per minute for black-chinned hummingbirds
- 265 beats per minute for broad-tailed hummingbirds
- 327 beats per minute for calliope hummingbirds
- 250 beats per minute for ruby-throated hummingbirds
So even while at rest, a hummingbird’s heart will beat between 225 and 327 times per minute on average, depending on the species. This rapid rate allows their heart to completely fill with blood and empty again over 20 times per second.
Heart rate while sleeping
Interestingly, a hummingbird’s heart rate slows down significantly when sleeping. During torpor, a hibernation-like state hummingbirds enter at night to conserve energy, their heart can slow to 50-180 beats per minute.
This allows them to reduce their metabolic rate by 50-95%. By slowing their heart and metabolism, hummingbirds are able to survive cold nights when they aren’t actively eating.
Maximum hummingbird heart rate during flight
A hummingbird’s heart beats the fastest when they are actively flying. The exertion and high energy demands of flying cause their heart rate to reach its maximum:
- Black-chinned hummingbird – 1,260 beats per minute
- Broad-tailed hummingbird – 1,200 beats per minute
- Calliope hummingbird – 1,260 beats per minute
- Ruby-throated hummingbird – 1,205 beats per minute
This means a hummingbird’s heart can beat over 20 times per second when they are flying! For comparison, a human heart at rest beats around 60-100 times per minute. During intense exercise, it may reach 160-200 beats per minute.
The tremendous increase in metabolism necessary for hummingbird flight is facilitated by this incredibly rapid heart rate. This allows oxygen and energy to be delivered at the rate their flight muscles require. No other animal’s heart beats as fast as a hummingbird’s during flight.
How is their heart rate measured?
Given how quickly a hummingbird’s heart beats, how do scientists accurately measure their heart rate? There are two main approaches:
Electrocardiogram (ECG)
An ECG records the electrical activity of the heart through electrodes attached to the skin. When hooked up to an ECG, the heart’s electrical signals are traced as waveforms on paper or displayed on a screen. This provides a readout of the heart rate.
Researchers can gently restrain a hummingbird and attach small electrodes to delicately measure its ECG and heart rate. However, this method may cause some stress that elevates the hummingbird’s heart rate above normal resting levels.
Doppler effect
A less invasive approach is to use the Doppler effect. This involves emitting high frequency sound waves towards an object in motion. The frequency of the reflected sound waves changes based on whether the object is moving closer or further away.
By recording the sound waves reflected off a hummingbird’s moving heart and converting the frequency changes into audible sounds, researchers can non-invasively measure the heart rate. When amplified, it sounds like a high-pitched chirping noise.
How does heart rate vary among hummingbird species?
There are over 300 different hummingbird species in the world. While they all have rapid heart rates, some patterns emerge when comparing heart rate across species:
- Smaller hummingbirds tend to have faster heart rates – The size of a hummingbird is strongly correlated with its heart rate. Smaller species like bee hummingbirds have the fastest heartbeat.
- Faster wingbeat also correlates with higher heart rate – Species with faster wingbeats, like Anna’s hummingbird, also tend to have faster heart rates.
- Hovering alone elevates heart rate – Hummingbirds that do more hovering have higher heart rates than species that prefer perching while feeding.
Below is a table comparing reported heart rates of various hummingbird species during flight:
| Species | Heart rate (beats per minute) |
|---|---|
| Bee hummingbird | 1,260 |
| Calliope hummingbird | 1,260 |
| Broad-tailed hummingbird | 1,200 |
| Black-chinned hummingbird | 1,260 |
| Rufous hummingbird | 1,200 |
| Ruby-throated hummingbird | 1,205 |
| Anna’s hummingbird | 1,204 |
| Allen’s hummingbird | 1,065 |
The bee hummingbird, the world’s smallest bird species, appears to have the fastest heartbeat measured in hummingbirds to date.
What controls hummingbird heart rate?
Hummingbirds have specialized adaptations that allow their heart rate to vary widely. The two key controllers of hummingbird heart rate are:
Pacemaker cells
Within the heart are specialized “pacemaker” cells that initiate rhythmic electrical impulses to trigger heartbeats. The pacemaker cells responsible for hummingbird heart rate can speed up or slow down heart rate very rapidly in response to changing energy needs.
Autonomic nervous system
The autonomic nervous system is comprised of the sympathetic and parasympathetic nervous systems. It regulates involuntary functions like heart rate.
The sympathetic nervous system prepares the body for action by accelerating heart rate, breathing, and metabolism. The parasympathetic system does the opposite – it slows heart rate and increases digestion and relaxation.
Hummingbirds have enhanced sympathetic and parasympathetic tone that allows their heart rate to vary widely as energy needs fluctuate.
How does metabolism affect heart rate?
Hummingbirds have among the highest mass-specific metabolic rates of any animal. The tremendous energy demands of hovering flight require lots of calories. To meet this need, hummingbirds have incredibly fast metabolisms.
Their fast metabolic rate is directly related to their rapid heart rate. Some key connections between hummingbird heart rate and metabolism include:
- High cardiac output – Faster heart rate means more blood pumped per minute (high cardiac output). This circulates oxygen and nutrients to match their metabolic demands.
- Enhanced blood oxygen capacity – Their blood has adapted to carry more oxygen thanks to higher levels of hemoglobin in red blood cells.
- High capillary density – More capillaries in their flight muscles bring blood closer to tissues needing oxygen.
Without their exceptionally fast metabolism and cardiovascular adaptations, hummingbirds could not fly as they do. The speed of their heartbeat is perfectly tuned to support their unique lifestyle.
Other animals with fast heart rates
While hummingbirds have the fastest known heart rate, some other animals also have cardiovascular systems adapted for speed. Here are a few other creatures with impressively rapid heartbeats:
Shrews – up to 1,200 bpm
These tiny mice-like mammals have very fast metabolism. Their heart beats up to 1,200 times per minute.
Small songbirds – 300-600 bpm
Small passerine birds like chickadees and finches have heart rates from 300-600 bpm while active. Larger birds tend to have slower heart rates.
Lab mice – 310-840 bpm
Mice have heart rates ranging from 310 to 840 beats per minute depending on their size and activity level.
Dogs – 60-180 bpm
On average, dogs at rest have heart rates from 60-120 bpm. During intense exercise, this can accelerate to 180-200 bpm.
Key adaptations that allow rapid heartbeat
In order to pump blood so quickly and meet the intense metabolic demands of flight, hummingbirds have evolved special cardiovascular adaptations:
- Enlarged heart chambers – Allows their small heart to hold more blood per beat.
- High hemoglobin – Their blood has adapted to carry more oxygen by increasing levels of oxygen-binding hemoglobin.
- Capillary dense flight muscles – More capillaries allow for rapid oxygen and nutrient delivery to their flight muscles.
- Low blood pressure – Less resistance allows blood to flow rapidly despite their incredibly fast heart rate.
These key adaptations allow hummingbirds to circulate oxygenated blood at rates necessary to sustain hovering flight and their extreme metabolic output.
Impacts of high heart rate
The hummingbird’s rapid heart rate helps enable their unique lifestyle but also carries some drawbacks, including:
- Higher risk of arrhythmias – There is less time between heartbeats, increasing the chance of abnormal heart rhythms.
- Increased oxidative stress – Their rapid metabolism can generate free radicals that must be neutralized.
- Higher dietary needs – They require frequent feeding on energy-rich nectar to fuel their metabolism and flight.
- Cool nighttime temperatures can be dangerous – Their rapid metabolism makes them vulnerable to cold exposure when not in torpor.
Nonetheless, the adaptations allowing hummingbirds’ extremely fast heart rate provide more benefits than downsides. Their rapid heartbeat enables hovering flight, nectar-feeding, and pollination.
Conclusion
A hummingbird’s incredibly fast heartbeat provides a fascinating look into how cardiovascular function can be pushed to the limits of what’s physically possible. The speed of their heart is perfectly tuned to provide the sustained energy output necessary for their hovering flight, rapid metabolism, and active lifestyle.
While other animals like shrews and small birds have rapid heart rates, none can match the hummingbird. At more than 20 beats per second while flying, they have the fastest heartbeat in the animal kingdom!
