Bat

Bats are flying mammals from the order Chiroptera and are the only mammals capable of true, sustained flight. They are more agile in flight than most birds, thanks to their long, spread-out digits covered by a thin membrane. The smallest bat, Kitti’s hog-nosed bat, measures 29–34 mm in length, while the largest, the giant golden-crowned flying fox, can weigh up to 1.6 kg and has a wingspan of 1.7 m.

Comprising about 20% of all classified mammal species globally, bats number over 1,400 species and are traditionally divided into megabats and microbats, though recent classifications have shifted to Yinpterochiroptera and Yangochiroptera. Many bats are insectivores, while others are fruit-eaters or nectar-eaters, and some species, like vampire bats, consume blood. They are predominantly nocturnal and often roost in caves, playing critical roles in ecosystems by pollinating flowers and dispersing seeds.

Bats possess flexible finger bones crucial for wing development, which allows for powered flight. Their wings are thinner and consist of more bones than bird wings, enabling precise maneuvers and energy-efficient flight. The wing membranes, or patagia, are delicate yet resilient, equipped with touch-sensitive receptors that help bats adapt to changing airflows during flight.

Bats roost upside down, a posture known as roosting, with their femurs allowing outward and upward bending during flight. While most megabats tuck their heads towards their bellies, microbats curl their necks backward, reflecting differences in cervical vertebrae. Their tendons enable them to lock their feet while hanging, requiring muscle power only to release.

On the ground, most bats crawl awkwardly, but some, like the New Zealand lesser short-tailed bat and the common vampire bat, can move agilely. Vampire bats use a bounding gait for speed, while short-tailed bats developed their movements in the absence of terrestrial mammal competitors, without compromising their flying ability.

Bats have an efficient circulatory system with strong venous muscle contractions that support blood flow back to the heart, preventing blood from rushing to their heads while roosting. Their highly adapted respiratory systems enable powered flight, demanding a large oxygen throughput. Bats’ wings are vascularized membranes, and their body structure allows for significant gas exchange efficiency, with wing surface area accounting for about 85% of their total body surface area.

Bats require about double the energy for flight compared to other mammals, leading to larger hearts—up to three times the size of terrestrial mammals of similar body mass—and heart rates reaching 1000 beats per minute. The digestive systems of bats vary based on diet; for example, insectivorous bats have specific enzymes to break down chitin, while vampire bats lack maltase due to their blood diet. Kidney adaptations also vary, with carnivorous bats having a structure suited for concentrated urine and frugivorous bats adapted for electrolyte retention.

Additionally, bats have higher metabolic rates that result in increased respiratory water loss. Their wings, composed of vascularized membranes, enhance evaporative water loss, which is crucial for maintaining ionic balance and thermoregulation. Female bats may have varying uterine structures, including either two uterine horns or a single chamber.

Microbats and some megabats use ultrasonic sounds for echolocation, with sound intensity influenced by subglottic pressure. Their cricothyroid muscle, located in the larynx, controls pulse frequency essential for this function. By comparing outgoing calls with returning echoes, bats can detect prey in darkness. Microbat calls range from 14,000 to over 100,000 Hz, far above human hearing (20-20,000 Hz).

Bats utilize low-duty cycle echolocation, timing short calls to avoid overlapping with echoes, and high-duty cycle echolocation, where continuous calls are separated by frequency using the Doppler effect. Bat ears, equipped with ridges akin to a Fresnel lens, help focus echolocation signals and detect prey sounds. They can estimate prey elevation using interference patterns from echoes reflecting off the tragus in their ears. Bats can create a mental image of their environment and prey through repeated echolocation scans.

Most microbat species have small, poorly developed eyes, resulting in limited visual acuity, though no species is completely blind. They possess mesopic vision, allowing them to see in low light but lacking color vision. Vision aids microbats in orientation between roosting and feeding grounds, as echolocation is effective only at short distances. Some species can also detect ultraviolet light and may distinguish colors due to their body coloration.

In contrast, megabat species often have eyesight that matches or surpasses human vision, adapted for both night and daylight, including some color vision.

During hibernation, bats enter a torpid state, reducing their body temperature for 99.6% of the time. They may occasionally show “heterothermic arousal,” where they briefly return to normal body temperature. In summer, some bats also become dormant during higher temperatures to stay cool.

The smallest bat is Kitti’s hog-nosed bat, measuring 29–34 mm in length and weighing 2–2.6 g. It competes with the Etruscan shrew for the title of smallest mammal. The largest bats, like species of Pteropus and the giant golden-crowned flying fox, can weigh up to 1.6 kg and have a wingspan of 1.7 m. Typically, larger bats use lower frequencies for echolocation, while smaller bats use higher frequencies to detect smaller prey. The adaptations of bat species affect their available prey.

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