Hummingbirds are a gift from nature. The surprising nature and anatomy of these mini creatures have intrigued scientists for a long time. Hummingbirds are also said to have a very high heart rate compared to humans. In this article, the various aspects of a hummingbird’s heart rate and metabolism are discussed.
With an average life expectancy of 3-5 years, hummingbirds have a fast metabolism and the highest heart rate measured in a hummingbird is 1,260 beats per minute when they are in full flight. This was recorded in a Blue-throated Hummingbird, however, these birds can lower their heart rate to 50-180 beats per minute based on the situation.
Among the 10,000 discovered species of birds, hummingbirds are known to be the tiniest of them all. In addition, adult hummingbirds grow to be only 3.3 inches (ca. 8 cm) in length and weigh about 0.07 to 0.7 ounces (ca. 26 g).
Hummers usually fly very long distances towards the north during the breeding season and south for the winter months. The ruby-throated hummingbird is known to fly around 500 miles without stopping while crossing the Gulf of Mexico. The Rufous hummingbird, from the genus Selasphorus, travels 3,700 miles (ca. 5,955 km) while flying from Mexico to Alaska. These birds are unique because of their unique anatomy, which prepares them for long-distance travel. They consume energy from the sugar present in nectar in flowers. Besides, hummer typically takes around 20 mins to digest the nectar and about 97% of the derived sugar is converted into energy falling them to travel thousands of miles without any rest.
Essentially, these factors lead to hummingbirds having a higher metabolic rate, which causes their heart rate to be higher.
While flying, hummingbirds can reach high heart rates. Then again, they can also lower their heartbeat at night while they sleep. This phenomenon is known as Torpor helps these birds to conserve energy. Hummingbirds tend to keep their heart rates down to as low as 50 to 250 beats per minute.
Hummers can also lower their temperature and metabolism by going into torpor, a state similar to hibernation. While sleeping, they also tend to hang upside-down from trees. Some hummingbirds even stop breathing for short durations to conserve energy as much as they can for daily activities or travel. Since hummingbirds have a fast metabolism, they consume a lot of nectar to meet their energy needs. Similarly, these birds can eat half their weight every day. Torpor prevents the birds from starving while resting, which is one of the most important factors.
Unlike their nature, female adult hummers do not experience torpor while sitting on the eggs. This helps the birds to use their body heat to warm their eggs during the night.
In general, hummingbirds calm their heart rates when they sense predatory threats or to survive the cold nights.
Hummingbirds are always on the move. Hence, this proactive lifestyle would require a great amount of energy. However, to consume this energy in their tiny bodies, hummers have a lot of capillaries. This is why they have a fast heartbeat that pumps blood rapidly around the blood vessels. Surprisingly, they have the largest heart as compared to their body size. Similarly, their brains make up around 4.2% of their total body weight.
Hummingbirds have the world’s highest heartbeat, which measures up to 1260 beats per minute. Besides, they have few natural predators which push these birds to have such extreme anatomy. Compared to humans, a hummingbird’s heart beats 10 times faster than a human. Consequently, they are more likely to suffer heart attacks, ruptures, and strokes. Considering their proactive nature (62 wing flutters per second), this might not be as surprising as it appears.
The structure of a hummingbird heart is four-chambered. The right portion of the heart functions as a receptor and receives blood coming from the systematic circulation and affects the pulmonary circulation. Moreover, this blood is further sent to the left portion where the left ventricle also affects the systematic circulation. Primarily, both sides of the ventricles receive blood at the central venous pressure before they enter their assigned tract.
As compared to the systematic portion, the peripheral resistance is usually less on the pulmonary area. This is why hummingbirds have the greater muscle mass to prevent the higher systematic resistance to balance the circulation on both sides of the ventricles.
The four chambers of a hummingbird heart are distinguished into two parts such as two atria and two ventricles. In various species, the right atrium of the avian heart is usually larger compared to the left. Similar to mammals, the wall of the heart is lined in layers: the endocardium, the inner lining, myocardium, middle lining, and the epicardium, the outer lining. Apart from that, the muscular myocardium present in the atria is thinner than the ventricles. These muscles are responsible for contraction and allowing the blood to enter the ventricles during ventricular diastole.
While these birds have a great heart rate compared to mammals, the atrioventricular (AV) valves of their heart are quite similar anatomically. Hence, the cusps are indistinct. However, the right AV has a singular layer of the myocardium which is affixed to the free wall.
Moreover, hummingbird hearts are positioned in the cranial portion of the thoracoabdominal cavity along with a long axis that is tilted slightly to the right. Besides, the heart is covered in a hard, fibrous, pericardial sac that has trace amounts of serous fluid used for lubrication.
Hummingbirds also have larger hearts compared to their overall size. This arrangement is observed in their anatomy due to the high aerobic activities of hovering which requires a lot of energy and a faster metabolism.