Hummingbirds are remarkable little birds that captivate people with their beauty, speed, and unbelievable heart rates. Their tiny hearts beat incredibly fast to support their high metabolism and enable them to hover and fly backwards.
Quick Facts
- A hummingbird’s heart can beat up to 1,260 times per minute.
- Their hearts beat up to 15 times per second while at rest.
- During flight, their heart rates can reach as high as 1,260 beats per minute.
- Hummingbirds take an average of 250 breaths per minute.
- Their high heart rate enables them to flap their wings up to 80 times per second.
With such rapid heart rates, hummingbirds have among the highest metabolism of all animals. Their hearts need to pump blood and oxygen at a breakneck pace to support their energy needs and power their wings during flight. Next, we’ll take a closer look at the physiology that allows for these astounding heart rates.
Anatomy of the Hummingbird Heart
A hummingbird’s heart is an incredible organ specialized for speed and efficiency to match their high-energy lifestyle. Here are some key anatomical features of their cardiovascular system:
- Their hearts account for 2.5% of their body weight, compared to just 0.5% in humans.
- The left ventricle, which pumps blood to the body, is particularly thick-walled and muscular to provide extra pumping power.
- They have the largest heart muscle relative to body size of all animals.
- Their hearts lack a left atrioventricular valve, which normally prevents backflow in other animals but would slow blood flow in hummingbirds.
In addition to specialized anatomy, hummingbirds have other physiological adaptations to support their racing hearts:
- Hemoglobin with a higher affinity for oxygen helps their blood pick up more oxygen.
- They have the highest capillary density ever measured, to supply their tissues with blood.
- They can shuffle and recruit capillaries as needed to route blood away from inactive tissues towards active flight muscles.
Altogether, these cardiovascular adaptations allow a hummingbird heart to beat at among the highest rates per minute of any animal on Earth.
Heart Rate While At Rest
Even while at rest, a hummingbird’s heart beats quite rapidly compared to other animals. Here’s how their resting heart rate measures up:
- Household cat – 120 to 140 beats per minute
- Adult human – 60 to 100 beats per minute
- Hummingbird – 250 to 500 beats per minute
This rapid resting rate is necessary to support their high metabolic rate. At rest, a hummingbird takes an average of 250 breaths per minute. Their muscles require a constant oxygen supply in order to generate enough energy to power basic biological functions. Without their racing heart pumping blood and oxygen while at rest, they would quickly suffocate.
Oxygen Consumption at Rest
At rest, hummingbirds consume around 4.8 milliliters of oxygen per gram of body weight per hour. Compared to other animals, this is an astounding rate:
| Animal | Oxygen consumption at rest (ml O2 / g / hr) |
|---|---|
| Shrew | 2.0 |
| Mouse | 1.8 |
| Sparrow | 1.6 |
| Hummingbird | 4.8 |
To meet these extreme oxygen demands while at rest, hummingbirds rely on their rapid heart rate to circulate oxygenated blood throughout their body and prevent tissue suffocation.
Heart Rate During Flight
In flight, a hummingbird’s oxygen consumption and heart rate increase dramatically. Hovering flight is particularly energy intensive. Here’s how their heart rate increases with different levels of activity:
- Resting – 250 to 500 bpm
- Moderate activity – 500 to 800 bpm
- Hovering flight – 800 to 1,200 bpm
- Fast flight – up to 1,260 bpm
When hovering, their oxygen consumption spikes to around 23 ml O2 / g / hr – nearly 5 times the rate at rest. This enormous energy expenditure is what drives their heart rate upwards of 1,200 beats per minute while flying.
Wing Beats and Heart Beats
In addition to rapid heart rate, hummingbirds flap their wings at incredible speeds to stay aloft. There is a direct link between their heart rate and wing beat frequency while hovering:
- Wing beats – 40 to 80 beats per second
- Heart beats – 10 to 15 beats per wingbeat
By synchronizing heart rate with wing beats, hummingbirds are able to maximize oxygen delivery during the most energetically intensive phase of each wingbeat cycle. This synchronization allows them to efficiently supply their flight muscles with the oxygen necessary to keep them hovering.
Fastest Heart Rates
Some hummingbird species have been recorded reaching peak heart rates at the upper levels of their range during flight:
- Blue-throated hummingbird – 1,205 beats per minute
- Calliope hummingbird – 1,260 beats per minute
- Broad-tailed hummingbird – 1,265 beats per minute
However, the habitat and context in which heart rate is measured impacts the maximum rate observed. Hummingbirds in captivity with restricted activity may not reach the same peak rates as active, free-living birds.
Additionally, small hummingbird species tend to have higher heart rates than larger species. Larger birds can carry more energy stores to power longer flights, while smaller birds need to sustain higher metabolism and heart rates to avoid starvation.
Highest Rates During Display Dives
Male hummingbirds perform display dives during courtship. During these high-speed power dives, they may reach peak heart rates:
- Average dives – 1,200 to 1,400 bpm
- Peak dives – as high as 1,600 bpm
By entering a steep dive, they are able to maximize heart rate and push their cardiovascular system to its limit when trying to attract females.
How Do Hummingbirds Survive Rapid Heart Rates?
Hummingbirds push their hearts to the verge of failure on a regular basis. When flying or diving, up to 10% of their total blood volume flows through their heart each second. Here are some ways they can tolerate these extreme heart rates:
- Their hearts have more coronary capillaries to supply the thickened walls with extra blood flow and oxygen.
- They may shunt blood away from other organs to protect the heart.
- Their cardiac cells have a large number of energy-producing mitochondria to keep up with demand.
Additionally, hummingbird hearts have molecular adaptations that allow the cardiac muscle to contract and relax rapidly without fatiguing. These specializations protect them from ischemia or arrhythmias during rapid heart rates.
Heart Rate Variability
Hummingbirds can alter heart rate rapidly depending on their activity level. This ability to vary rate protects them from danger:
- Rate can increase 75% within 0.08 seconds if they sense a threat.
- Being able to instantly accelerate heart rate gives them an advantage in evading predators.
By having such nimble control over heart rate, hummingbirds can balance their extreme energy needs with their small body size and survive operating at their physiological limit.
Impact of Temperature on Heart Rate
Like all avian species, hummingbirds are endothermic and must regulate their internal body temperature to survive. Cool external temperatures force hummingbirds to increase heart rate to produce more internal heat through metabolic activity:
- Exposure to 54°F temperatures increased heart rate by 35% in one study.
- At freezing temperatures, their heart may beat up to 1,300 times per minute just to maintain body heat.
This substantial increase in heart rate to compensate for cooler conditions requires more oxygen and calories. As a result, hummingbirds are extremely vulnerable to starvation or cold stress when food sources are scarce or temperatures drop.
Torpor
To cope with low temperatures, hummingbirds can enter a state of torpor in which their metabolic and heart rates are drastically reduced. This torpid state helps preserve energy reserves:
- Heart rate drops from 500 bpm to 50-180 bpm.
- Breathing slows from 250 breaths/min to 30-90 breaths/min.
- Body temperature falls from 104°F to 60-68°F.
Torpor allows the hummingbird to rest and survive periods of cold, but they may need to fully awaken every hour to avoid organ damage from low body temperatures.
Impact of Altitude on Heart Rate
At high altitudes, lower oxygen availability presents an additional challenge for hummingbirds. Studies found:
- Hummingbirds at 10,500 feet altitude had higher heart rates than those at sea level.
- Those living at higher altitudes had enlarged hearts compared to lowland relatives.
To compensate for lower oxygen at altitude, hummingbirds have adapted by increasing heart size and stroke volume. However, altitudes above 14,500 feet may exceed their cardiovascular capabilities.
Highest Altitude Hummingbirds
Some Andean hummingbird species inhabit elevations up to 17,000 feet through adaptations like larger hearts and wings:
| Species | Maximum Altitude |
|---|---|
| Giant hummingbird | 14,950 feet |
| Amethyst-throated sunangel | 15,750 feet |
| Andean hillstar | 17,060 feet |
Their cardiovascular adaptations allow them to thrive in low oxygen environments that would cause heart failure in other hummingbirds.
Do Hummingbirds Get Heart Disease?
Surprisingly, hummingbirds appear relatively resistant to cardiac diseases like arrhythmias or heart attacks despite their extreme cardiovascular demands. Potential explanations include:
- Exercise from continuous flying may protect their heart health.
- They have genes to repair cardiac cell damage and prevent fibrosis.
- Dietary antioxidants from nectar may reduce molecular damage.
- Fast heart rate prevents blood from pooling and clotting.
However, narrowing or stiffening of arteries due to cholesterol does appear to be an issue in captive hummingbirds. Providing a balanced diet in captivity is important to maintain their heart health into old age.
Short Lifespans
In the wild, most hummingbirds will not live more than 5 years even with a robust cardiovascular system. Reaching maximum lifespan potential requires ideal conditions with no environmental stressors. Their short lifespans in the wild likely preclude many heart diseases from becoming clinically apparent.
Monitoring Heart Rate in Hummingbirds
Given their tiny size, measuring heart rate in hummingbirds requires specialized techniques and equipment. Some approaches include:
- Listening to their chest with a stethoscope.
- Feeling pulsations through their skin.
- Using an electronic sensor pad adhered to their skin.
- Measuring Doppler shifts in reflected sound waves.
- Tracking pulsations with high-speed video of their neck or wings.
Collecting heart rate data from wild hummingbirds can be challenging. Minimizing stress is crucial when trapping birds to attach electronic sensors. Their heart will naturally accelerate due to a fight-or-flight response.
Training Hummingbirds
Researchers have had success training hummingbirds to perch on special stations equipped to record heart rate. This voluntary data collection minimizes stress artifacts in the measurements.
Conclusion
A hummingbird’s heart is an incredible marvel of nature and evolution. Their ability to reach sustained heart rates over 1,200 beats per minute is one of the adaptations that enables their unique lifestyle and aerobatic abilities. Next time you see a hummingbird hover at a flower, appreciate what an extraordinary organ is powering its flight!
