Hummingbirds are remarkable little creatures, able to hover in midair and fly backwards using their specialized wings that beat up to 80 times per second. Their high metabolism and heart rate help support their energetic lifestyle. But does this also put them at higher risk for heart attacks?
What is a heart attack?
A heart attack, also called a myocardial infarction, occurs when blood flow to part of the heart muscle is severely reduced or stopped completely. This happens because the arteries supplying blood to the heart muscle are narrowed or blocked, often due to a buildup of plaque. Without oxygen from the blood, the heart muscle starts to die.
In humans, common signs of a heart attack include chest pain or discomfort, shortness of breath, nausea, and sweating. Heart attacks require emergency medical treatment. Prompt action helps limit damage to the heart muscle.
Do hummingbirds have hearts?
Yes, hummingbirds have hearts. A hummingbird’s heart is relatively large compared to its body size. The average adult hummingbird heart is about 0.2 grams, while the average adult hummingbird weight is around 3-6 grams.
Their hearts beat incredibly fast, with average resting heart rates of 250-600 beats per minute. During flight, their hearts can reach up to 1,200 beats per minute. This rapid heart rate powers their wings for hovering and supports their high metabolic rate.
Hummingbird Heart Health Risks
Hummingbirds have several anatomical and physiological adaptations to support their high heart and metabolic rates. But there are some risks associated with their cardiovascular systems as well.
Heart attacks
It is possible for hummingbirds to suffer heart attacks, though the research is limited. One older study from the 1960s examined 225 rufous hummingbird hearts and found evidence of past myocardial infarctions in 2 of them. This suggests that while rare, heart attacks can occur in hummingbirds.
Contributing factors likely include natural aging, congenital abnormalities, hypertension, and ischemia from any obstruction of blood flow. One case report documented a heart attack in a Broad-billed Hummingbird following a period of extreme cold. Hypothermia stressed the bird’s cardiovascular system.
More research is needed to understand the prevalence of myocardial infarctions in different hummingbird species across age groups, habitats, and activities. Autopsies of deceased hummingbirds could reveal valuable data.
Arrhythmias
Hummingbirds can experience arrhythmias, which are irregular heart rhythms. These disrupt the normal sequential pumping of the four heart chambers.
One study monitored heart rates in Anna’s and Costa’s hummingbirds. Both species showed episodes of arrhythmia. These included skipped beats, premature contractions, and a rapid but sporadic heart rhythm called fibrillation. Such arrhythmias may result from abnormal pacemaker cells or disrupted electrical signaling in the heart.
Research into how factors like age, genetics, diet, habitat pollution and climate change impact hummingbird arrhythmias would be illuminating. Arrhythmias may contribute to premature mortality.
Enlarged hearts
The high blood pumping demands on hummingbird hearts leads to physiological cardiac hypertrophy. This means their hearts enlarge naturally as an adaptive mechanism. Hearts of hummingbird species specializing in sustained hovering tend to be larger.
But in some cases, pathological enlargement of the heart muscle, called cardiomegaly, can result from hypertension or weakness in heart contractions. This may reduce pumping capacity and oxygenation. However, more studies in live, wild hummingbirds would help differentiate between adaptive and pathological enlargement.
| Heart Risk Factor | Potential Cause |
|---|---|
| Myocardial infarction | Aging, congenital defects, hypertension, hypothermia |
| Arrhythmias | Abnormal electrical signaling |
| Cardiomegaly | Hypertension, contractility issues |
Unique Attributes of Hummingbird Cardiovascular Systems
Hummingbirds have several key adaptations that allow their cardiovascular systems to meet extreme metabolic and energy demands.
Specialized heart anatomy
A hummingbird’s heart has:
– Thick muscular walls to handle the pressure of high heart rates. This gives their hearts a disproportionately large appearance.
– Larger left ventricle compared to the right ventricle. This pumps oxygenated blood to the entire body. The left ventricle wall may be 3-4x thicker than the right.
– Enlarged atria to hold returning blood. This helps coordinate the rapid heart rate cycles.
– Higher capillary density and mitochondria content to produce energy aerobically. This supports contractility at high pumping speeds.
Fast heart rate response
Hummingbirds can quickly adjust their heart rate as energy demands change. For example:
– Heart rate increases within 1-2 wing beats when transitioning from perching to flight.
– Heart rate variability is low during hovering flight (high energy cost), indicating stability.
– Heart rates drop during periodic breathing cycles mid-flight, allowing partial recovery.
This responsiveness matches energy output closely to needs and avoids overworking the cardiovascular system.
Low blood pressure
Hummingbirds have relatively low blood pressure compared to mammals. Systolic blood pressure ranges from ~115-150 mm Hg in Anna’s hummingbirds. For comparison, human systolic blood pressure should be less than 120 mm Hg.
This lower pressure allows blood flow even at very high heart rates. It minimizes stress on arteries and capillaries while supplying tissues.
Behavioral and Environmental Support
Hummingbird behaviors and environmental factors also appear to support cardiovascular health.
Rest periods
Hummingbirds generally alternate rapid bursts of feeding and flying with periods of rest throughout the day. During rest, heart and breathing rates slow considerably, which likely aids cardiovascular recovery. Young fledglings spend more time resting than mature adults until their strength builds.
Temperature regulation
Hummingbirds have high thermogenic capacity and are adept at maintaining optimal body temperature in different environments through adjustments like piloerection (feather fluffing) and altering respiration. This helps avoid hypothermia stress and reduce myocardial strain.
Antioxidants
Flowers and nectar contain antioxidants including vitamin C and carotenoids. When consumed, these may help neutralize damaging molecular byproducts of hummingbirds’ high metabolic rates. However, more research is needed on antioxidant benefits for hummingbirds.
Fasting capability
Hummingbirds can enter torpor, a hibernation-like state, to conserve energy when food is scarce. Their metabolic rate slows up to 95%. This significantly reduces cardiovascular demands and strain during environmental stress.
| Supporting Factor | Cardiovascular Benefit |
|---|---|
| Rest periods | Cardiac recovery |
| Temperature regulation | Avoids hypothermia strain |
| Dietary antioxidants | Reduces molecular damage |
| Torpor use | Lowers cardiovascular demands |
Conclusion
In conclusion, hummingbirds have a number of anatomical and behavioral adaptations that allow their cardiovascular systems to meet the extreme demands of hovering flight and their high metabolism. Their hearts are specially equipped to pump at very rapid rates throughout the day. While heart attacks, arrhythmias, and enlargement can occur, these appear rare based on limited data. Rest, temperature regulation, antioxidants, and torpor help support cardiovascular function and reduce total stress. More research tracking wild hummingbird heart health across environments would provide greater insight into the prevalence of cardiac issues and risks. With appropriate adaptations and support, however, hummingbirds are able to maintain impressive cardiovascular vigor. This enables their unique and captivating way of life.
