Hummingbirds are amazing little birds that have fascinated people for centuries with their unique ability to hover in midair and fly backwards and upside down. One of the most intriguing things about hummingbirds is how their tiny hearts beat incredibly fast, even up to over 500 beats per minute when they’re flying. This has led to a common myth that a hummingbird’s heart will stop beating if they stop flying. But is this really true? Let’s take a closer look at the physiology and flight dynamics of hummingbirds to find out.
Hummingbird Heart Rate
A hummingbird’s heart rate is among the fastest of any animal on Earth. Their hearts beat up to 25 times per second while at rest. This rapid rhythm powers their high metabolism and provides the energy they need to flap their wings up to 80 times per second. During flight, their heart rate accelerates to over 500 beats per minute in order to pump enough oxygenated blood to power their wing muscles.
The extremely fast heart rate of hummingbirds is an adaptation that allows them to meet the high energy demands of hovering flight. Hovering is inherently unstable and requires constant minor corrections and a lot of power. The fast heart rate ensures their wing muscles get a constant supply of oxygen and energy.
So while hummingbirds do have a very fast heartbeat when flying, their hearts continue to beat even when perched and at rest. The rapid rate slows down when they stop flying, but it does not completely stop.
How Hummingbirds Hover and Rest
Hummingbirds are the only birds that can truly hover. They can beat their wings up to 80 times per second, allowing them to generate enough lift to stay suspended in one place. This takes an immense amount of energy and requires a lightning-fast metabolism.
But hummingbirds cannot maintain hovering flight indefinitely. They must periodically stop to rest, just like any other animal. When hummingbirds rest, they will perch on branches, wires, or other surfaces. Their wings will stop beating, but their heart continues pumping at a slower, resting rate to keep their organs functioning.
Hummingbirds can enter a hibernation-like state called torpor to conserve energy. During torpor, their metabolic rate slows down dramatically and their heart rate drops to just 50-180 beats per minute. Even in this energy-saving state, their hearts continue to beat to supply their organs with blood. They can arouse quickly from torpor when needed.
What Happens if a Hummingbird’s Heart Stops?
If a hummingbird’s heart does stop completely, the results would be fatal within minutes. Like all animals, hummingbirds depend on their cardiovascular system to deliver oxygen and nutrients to their tissues. Without blood circulation, their brains, muscles, and other organs would quickly become damaged.
Hummingbirds have proportionately larger hearts than other birds and very high oxygen demands. If their heart stops, their high metabolism rapidly depletes their limited energy reserves. Their small body size means they cannot tolerate interrupted blood flow for more than a few minutes before organs sustain permanent damage.
A stopped heart would also impair their ability to control their wing muscles and maintain flight. This would cause the hummingbird to fall out of the air. If its heart does not restart almost immediately, the impact with the ground would likely be fatal.
For all these reasons, it is unlikely a hummingbird’s heart would ever completely stop, even temporarily, outside of terminal illness or trauma. Their cardiovascular system is designed to operate continuously to meet their extreme metabolic requirements.
Measurements of Hummingbird Heart Rate
Scientists have quantitatively measured hummingbird heart rate during flight and rest by attaching tiny electrodes near their hearts to record cardiac activity. This allows precise numbers to be put the beating of their tiny hearts.
One study measured the resting heart rate of broad-tailed hummingbirds at around 250 beats per minute. During hovering, this accelerated to as high as 1,260 beats per minute. In another experiment, calliope hummingbirds showed heart rates of 600-1,250 beats per minute while feeding on nectar from flowers.
These studies empirically demonstrate that hummingbird hearts keep beating even when not engaged in sustained hover-feeding. Their hearts slow down but do not cease during rest periods.
Table 1. Hummingbird heart rate measurements
| Activity | Heart Rate Range |
|---|---|
| At rest | 180-250 bpm |
| Hovering flight | 500-1250 bpm |
| Torpor | 50-180 bpm |
Physiological Reasons a Hummingbird’s Heart Doesn’t Stop
There are several key physiological reasons why a hummingbird’s heart does not stop when it ceases flying:
High Metabolic Rate
Hummingbirds have an extremely fast metabolism that requires a constant supply of oxygen that would be interrupted if their heart stopped. Their basal metabolic rate is the highest of any homeothermic animal.
Small Body Size
With a very small body mass, hummingbirds have limited energy reserves. If their heart stopped, their fast metabolism would quickly deplete their energy stores and they would die. Their small size means they need a continuously beating heart.
Thermoregulation
Hummingbirds have high body temperatures around 105°F that must be maintained through rapid metabolism. Their heart needs to keep beating steadily to regulate their body temperature, even when at rest.
Low Stroke Volume
Despite having a fast heart rate, each beat has a relatively low stroke volume. This necessitates more beats per minute to meet metabolic needs. If their heart rate drops below a critical level, blood flow would be insufficient.
High Blood Oxygen Saturation
Hummingbird blood has the highest hemoglobin saturation of any animal, storing more oxygen than most birds and mammals. But this blood still requires constant circulation and cannot sustain the animal if the heart stops.
Evolutionary Adaptations That Prevent Heart Stoppage
Hummingbirds have evolved over millions of years to have cardiovascular systems capable of providing continuous blood circulation during both high-intensity flight and rest:
Enlarged Heart
Hummingbirds have proportionately larger hearts compared to other birds and extremely thick heart walls to sustain high pulse rates. This prevents arrhythmias or interruptions.
Efficient Lung System
Their lungs have adapted to efficiently supply oxygen to the bloodstream and remove carbon dioxide even when beating their wings up to 80 times per second.
Capillary Dense Muscles
Their wing muscles are packed with capillaries that provide ample blood flow. This allows their heart to keep their muscles continuously supplied with nutrients and oxygen.
Low Blood Pressure
Hummingbirds have adapted to have relatively low blood pressure compared to other birds and mammals with similarly fast heart rates. This reduces stress on the cardiovascular system.
Rapid Respiration
They can take up to 250 breaths per minute, further ensuring their high oxygen needs are met by their constantly circulating blood.
Conclusion
In summary, hummingbirds have a rapid heart rate that speeds up during flight but continues beating steadily even when they are perched at rest. Their unique physiology and adaptations allow their cardiovascular system to pump blood continuously without ever having to stop. While hummingbird hearts beat incredibly fast during flight to power their wing muscles, they do not completely stop when a hummingbird ceases flying. The nonstop heart rate may slow down significantly, but it provides critical circulation at all times to supply their high-energy demands. So while hummingbird hearts beat remarkably fast, they never truly stop.
