New Hampshire Public Radio | By Outside/In,
PublishedJanuary 6, 2023 at 6:00 AM EST
Every other Friday, the Outside/In team answers a listener question about the natural world. In this week’s question from Alyssa via Instagram, we consider adaptations different animals make to survive winter:
How slow can an animal's heartbeat get without it dying? So how many beats per minute are needed to keep an animal alive? And how does this change with hibernation and other behaviors?
The size of an animal is generally what determines how often its heart beats, or its beats per minute (BPM). Small animals have a faster breathing and heart rate because they lose heat through their skin faster than big animals do. They need to produce energy and heat at a faster pace and then redistribute it repeatedly through their body as it disperses. For example, the hummingbird has a heart rate of 1,000 beats per minute.
Both large and small animals adapt their heart rates
The largest mammal, the blue whale, has a heart the size of a sofa, and their heart beats have been recorded as low as two per minute. That's the slowest heartbeat of any warm blooded mammal.
Goldbogen Lab/Duke Marine Robotics and Remote Sensing Lab; NMFS Permit 16111
Some animals employ an involuntary survival strategy called torpor to survive winter and the lack of food. Not only does the heart rate drop, but so does body temperature, breathing rate and metabolism. In hibernating black bears, torpor causes the heart rate to drop from an average of 55 down to about 14 beats per minute.
Hummingbirds can experience torpor to conserve energy every night, even a cold summer night. They can vary the level from shallow to deep torpor. Their heart rates drop from that super-rapid 1,000 beats per minute to as slow as 180 to 50 beats per minute on a cold winter’s night.
How cold-blooded animals adapt to winter
And then there are animals who can put their heartbeat and respiration on pause all winter without dying. It's called brumation, and it's essentially hibernation for cold-blooded animals.
That's how some frogs, like the wood frog and spring peepers, survive winter. They overwinter by burrowing into mud or leaf litter and stay there, seemingly dead, no breathing or heartbeat. They are able to do this by flooding their cells with glucose which acts like antifreeze in their bodies, preventing the water in their cells from freezing and expanding. While they appear solidly frozen, they are only about 70% frozen.
Come spring, they defrost in about an hour, and hop on their way with a normal heart rate of 40 to 50 beats per minute.
Turtles use this adaptation as well. A turtle's heart beats about 40 beats per minute when they're basking in the sun in the summer. But during the winter, when they're buried in the mud at the bottom of the lake or in the woods, their heartbeat drops to about one beat every 10 minutes.
Did you ever think about snakes in winter?
Snakes are also able to slow down their heart rates to almost nothing. Some snakes use “communal brumation” in a den beneath the frost line. They gather in a clump of hundreds (or even thousands) of snakes, and go dormant, all bundled up together to conserve energy and protect themselves from the cold.
Learn more:
Stanford researchers report first recording of a blue whale’s heart rate
Overwintering for amphibians and reptiles
How Do Hummingbirds Survive Snow and Cold Weather?
Submit your question about the natural world to the Outside/In team. You can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org or call the hotline, 1-844-GO-OTTER.
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I'm an avid enthusiast and expert in the field of animal physiology, particularly focusing on adaptations that allow creatures to thrive in challenging environmental conditions. My knowledge extends across various species and their remarkable abilities to survive the harsh winter months. Let's delve into the concepts covered in the article from New Hampshire Public Radio, where the Outside/In team explores the question posed by Alyssa about how slow an animal's heartbeat can get without causing harm, and how this varies with hibernation and other behaviors.
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Heartbeat Variation Based on Size: The article highlights that the size of an animal plays a crucial role in determining its heartbeat. Smaller animals, like hummingbirds, have faster heart rates and breathing rates due to their higher surface area-to-volume ratio, which leads to faster heat loss. For instance, a hummingbird boasts an astonishing heart rate of 1,000 beats per minute.
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Blue Whale's Slow Heartbeat: On the other end of the spectrum, the blue whale, the largest mammal, demonstrates an intriguing adaptation. Despite its massive size, the blue whale's heart rate has been recorded as low as two beats per minute, marking the slowest heartbeat among warm-blooded mammals. This adaptation allows the blue whale to efficiently regulate energy consumption.
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Torpor and Hibernation: Animals, both large and small, may enter a state of torpor during winter to survive the scarcity of food. Torpor involves a significant drop in heart rate, body temperature, breathing rate, and metabolism. Hibernating black bears, for example, experience a decrease in heart rate from an average of 55 to about 14 beats per minute during torpor.
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Hummingbirds and Torpor: Even hummingbirds, known for their high metabolism, can enter torpor during cold nights, reducing their heart rate from 1,000 beats per minute to as slow as 180 to 50 beats per minute. This adaptive strategy helps them conserve energy.
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Brumation in Cold-Blooded Animals: Cold-blooded animals, such as frogs and turtles, exhibit a unique winter survival strategy called brumation. They can essentially put their heartbeat and respiration on pause without dying. Frogs like the wood frog and spring peepers, as well as turtles, utilize brumation by lowering their metabolism and flooding their cells with glucose to prevent freezing.
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Communal Brumation in Snakes: Snakes employ a fascinating behavior known as "communal brumation." They gather in dens beneath the frost line, slow down their heart rates, and go dormant in large groups to conserve energy and protect themselves from the cold. This communal strategy involves hundreds or even thousands of snakes bundled together.
These remarkable adaptations showcase the diverse ways in which animals navigate the challenges of winter, from the smallest hummingbird to the largest blue whale, each employing unique physiological strategies to ensure survival. If you have any further questions or topics you'd like me to explore, feel free to ask!
