Bats have gotten particularly bad press lately, so I‘m devoting my April blog posts to our mammalian friends.
Yes, bats are mammals and we, as humans are actually „more closely related to bats than we are to dogs, cows or whales.“ says Clint Witchalls in the academic journal The Conversation. „Bats are the most unusual of the world’s 26 mammal orders, or large groups, such as rodents and carnivores. They are the only land mammals that navigate by echolocation, and the only mammals capable of true flight.“
Bats are not only unique in the mammal family but, unlike ourselves, a keystone species. „Bats are key-role players in insect consumption and keeping insect populations in balance, pollinating flowers and dispersing plant seeds. They sustain whole ecosystems from rainforests to deserts; they live on remote Pacific islands to the Andes.“ says bat expert Merlin Tuttle in an article for National Geographic. „One bat can catch over 1,000 mosquito-sized insects in a single hour. … Without bats we could be buried in pests. They are critically important to the ecosystem and if we would let them, they would help us reduce our dependence upon pesticides by controlling crop pests.
I don’t know of any group that is more fascinating or diverse. They’ve been around since the age of dinosaurs; they were here tens of millions of years before there was ever a human on the planet.“
Bats are also very social animals, they form what we would call „friend-ships“, assisting each other with child care and grooming and sharing food for those in need.
Since this is a blog about breathing, I‘d also like to share with you the amazing respiratory and cardiovascular features of bat bodies. In Wikipedia I found out that “Bats possess a highly adapted respiratory system to cope with the demands of powered flight, an energetically taxing activity that requires a large continuous throughput of oxygen. In bats, the relative alveolar surface area and pulmonary capillary blood volume are larger than in most other small quadrupedal mammals. During flight the respiratory cycle has a one-to-one relationship with the wing-beat cycle. Because of the restraints of the mammalian lungs, bats cannot maintain high-altitude flight.
The wings are highly vascularized membranes, the larger blood vessels visible against the light. It takes a lot of energy and an efficient circulatory system to work the flight muscles of bats. Energy supply to the muscles engaged in flight require about double the amount compared to the muscles that do not use flight as a means of mammalian locomotion. In parallel to energy consumption, blood oxygen levels of flying animals are twice as much as those of their terrestrially locomoting mammals. As the blood supply controls the amount of oxygen supplied throughout the body, the circulatory system must respond accordingly. Therefore, compared to a terrestrial mammal of the same relative size, the bat’s heart can be up to three times larger, and pump more blood. Cardiac output is directly derived from heart rate and stroke volume of the blood; an active microbat can reach a heart rate of 1000 beats per minute.
With its extremely thin membranous tissue, a bat’s wing can significantly contribute to the organism’s total gas exchange efficiency. Because of the high energy demand of flight, the bat’s body meets those demands by exchanging gas through the patagium of the wing. When the bat has its wings spread it allows for an increase in surface area to volume ratio. The surface area of the wings is about 85% of the total body surface area, suggesting the possibility of a useful degree of gas exchange. The subcutaneous vessels in the membrane lie very close to the surface and allow for the diffusion of oxygen and carbon dioxide.”
A study by Mauricio Canals L, Iriarte-Diaz and Bruno Grossi shows that bats have “lung volumes about 72% greater than non-flying mammals of the same size.” Bats are masters in adaptation, their “Pulmonary ventilation can rapidly increase 10 to 17 times as flight begins. These respiratory adaptations, along with structural changes of lungs, lead to higher oxygen consumption than other mammals of similar size, reaching up to 22 mlO2/gh at low temperatures and during hovering. … In addition, bats have a very thin alveolar-capillary barrier, yielding an oxygen diffusion capacity similar to birds. Also, the heart of bats is larger than in all other mammals, representing about 1% of body weight, reaching in some cases 2%. Birds and bats reach very similar aerobic capacities. However, while birds have a large set of structural changes in their respiratory system, bats have a cardiorespiratory system optimized to their extreme life style.”
A bat’s heart rate changes dramatically, from ca. 300 – 200 beats per minute during resting to the aforementioned 1000 beats per minute during flight. If it didn’t, bats couldn’t survive a night hunting for food. They would burn through their own fuel, so to speak. “Several times each hour, the bats lowered their already slowed heart rates from about 300 beats per minute down to 200 beats per minute for about 6 minutes.”, observed researchers, cited in Science magazine. “Over the course of a day this saves 10% of their daily energy budget, the researchers report. “This could be the difference between life and death over a season.”
So, as we can see, there is much to learn from bats and much to thank them for.