The Only Mammals That Can Fly: Bats Explained

Bats are the only mammals capable of true powered flight, a distinction that sets them apart from every other mammal on Earth. While flying squirrels, colugos, and other gliding mammals can move through the air, they do so by descending from a higher point and cannot generate lift to climb or maintain level flight. This article explains the anatomical and physiological basis of bat flight, compares bats with gliding mammals, and addresses common questions about these remarkable animals.

At a Glance: Bat Flight vs. Gliding in Mammals

What Makes Flight Different from Gliding

True powered flight requires the animal to generate enough lift to overcome its body weight and enough thrust to move forward through the air. Bats accomplish this through rapid flapping of their wings, which are modified forelimbs with an elastic membrane stretched between elongated finger bones. This membrane, called the patagium, extends from the body to the tips of the digits and continues to the hindlimbs in many species.

Gliding mammals, by contrast, use a membrane that stretches between their limbs but do not flap it. They launch from a high point and descend at an angle, using their body position to control direction and speed. The distinction matters for understanding the evolutionary history of flight and for practical purposes such as identifying animals observed in the field.

According to research published in PeerJ, bats are the only mammals capable of powered flight and have correspondingly specialized body plans, particularly in their limb morphology. The same study notes that the origin of bat flight is still not fully understood due to an uninformative fossil record, but it is widely hypothesized that bats evolved from gliding ancestors. The researchers used phylogenetic comparative methods to model the evolution of forelimb and hindlimb traits across four extinct bats and 231 extant mammals with diverse locomotor modes. Their results revealed that gliders exhibit adaptive trait optima toward relatively elongate forelimbs that are intermediate between those of bats and non-gliding arborealists, and toward relatively narrower but not longer hindlimbs that are intermediate between those of non-gliders and bats. This supports a hypothetical evolutionary pathway wherein glider-like postcranial morphology precedes a bat-like morphology adapted to powered flight. See the full study at PubMed.

The Three Vertebrate Lineages with Powered Flight

Bats belong to an exclusive group in the history of life. Research published in Biological Reviews of the Cambridge Philosophical Society states that throughout the evolutionary history of life, only three vertebrate lineages took to the air by acquiring a body plan suitable for powered flight: birds, bats, and pterosaurs. Pterosaurs were the earliest vertebrate lineage capable of powered flight and included the largest volant animal in the history of the earth. The study examines how pterosaurs evolved their flight apparatus, focusing on the disproportionately elongated fourth finger and the wing membrane called the brachiopatagium, which stretches from the posterior surface of the arm and elongated fourth finger to the anterior surface of the leg. See the full study at PubMed.

This evolutionary context helps explain why bats are unique among mammals. Birds achieved flight through modification of the forelimb into a feathered wing, and pterosaurs used an elongated fourth finger to support a membrane. Bats independently evolved a similar solution using elongated digits, but they are the only mammals to have done so.

Anatomical Adaptations for Powered Flight

Wing Structure and Forelimb Morphology

The bat wing is a modified forelimb with several distinctive features. The bones of the wing are elongated, particularly the digits, which spread to support the wing membrane. The membrane itself is thin, elastic, and richly supplied with blood vessels and sensory nerves. This structure allows the wing to change shape during flight, enabling precise control of lift and thrust.

Research on the somatosensory substrates of flight control in bats, published in Cell Reports, demonstrates that wing sensory innervation differs from other vertebrate forelimbs. The study, conducted on the big brown bat (Eptesicus fuscus), found that the wing is innervated by an unusual complement of sensory neurons poised to report airflow and touch. Cortical neurons encode tactile and airflow inputs with sparse activity patterns. The authors conclude that evolutionary pressures giving rise to mammalian flight led to unusual sensorimotor projections. See the full study at PubMed.

This sensory system is critical for flight control. Bats must process information about airflow over the wing surface, wing position, and obstacles in their environment while making rapid adjustments to their flight path. The integration of touch and airflow sensing allows bats to fly with remarkable agility in dense vegetation and dark conditions.

Body Plan and Limb Proportions

The overall body plan of bats reflects the demands of powered flight. The forelimbs are disproportionately long compared to the hindlimbs, and the bones are lightweight yet strong. The sternum has a keel for attachment of the powerful flight muscles, similar to the condition in birds. The shoulder joint is highly mobile, allowing a wide range of wing motion.

The hindlimbs of bats are relatively small and are rotated so that the knees point backward. This arrangement allows bats to hang upside down from roosts, a posture that facilitates takeoff. Because bats cannot launch into flight from the ground easily, they typically drop from a roost or perch to gain altitude.

Metabolic and Physiological Demands

Powered flight is energetically expensive. Bats experience extreme physiological conditions rarely encountered by other mammals, including high metabolic demands and temperature fluctuations during flight. Research published in Cell Reports on the Jamaican fruit bat (Artibeus jamaicensis) placenta describes these conditions and notes that bats are a powerful model for understanding placental adaptation during pregnancy. The study found that bat trophoblast organoids maintain high basal antiviral gene expression but limited inducibility following viral stimulation, revealing a unique strategy of immune vigilance without inflammation at the maternal-fetal barrier. See the full study at PubMed.

The high metabolic demands of flight have broader implications for bat biology. A study published in Emerging Infectious Diseases hypothesizes that flight, a factor common to all bats but to no other mammals, provides an intensive selective force for coexistence with viral parasites through a daily cycle that elevates metabolism and body temperature analogous to the febrile response in other mammals. On an evolutionary scale, this host-virus interaction might have resulted in the large diversity of zoonotic viruses in bats. See the full study at PubMed.

Echolocation and Sensory Systems

How Echolocation Works

Most bat species use wideband echolocation signals to navigate dense forests and hunt for evasive insects in the dark. Research published in Sensors reviews target tracking and interception by echolocating bats and highlights biological solutions that could inform new approaches to artificial sonar tracking and navigation systems. Bats exhibit rapid adaptations in flight trajectory, sonar beam aim, and echolocation signal design, which appear to be key to their success in a variety of tasks. See the full study at PubMed.

Echolocation involves emitting high-frequency sounds and listening to the echoes that return from objects in the environment. By analyzing the timing, frequency, and intensity of these echoes, bats can determine the location, size, shape, and movement of objects, including prey and obstacles. This system is so precise that some bats can detect and capture insects as small as mosquitoes in complete darkness.

Ear Morphology and Muscle Control

The ability to move the ears independently is essential for echolocation. Research published in the Journal of Veterinary Medical Science examined the caudal auricular muscles in the greater short-nosed fruit bat (Cynopterus sphinx), a pteropodid that lacks laryngeal echolocation. The study found three cervicoauricularis muscles in this species, comparable to those of non-bat boreoeutherian mammals and yangochiropterans. The authors suggest that pteropodids and yangochiropterans maintain the general condition of boreoeutherian mammals and that rhinolophoids have a derived condition. See the full study at PubMed.

This research highlights the diversity of ear muscle arrangements among bat groups and their relationship to echolocation ability. Bats with laryngeal echolocation have delicate ear movements that are essential for their sonar system, while fruit bats that do not echolocate have a more general mammalian ear muscle pattern.

Sensory Biology and Ecomorphology

A special issue of The Anatomical Record dedicated to bat biology covers broad themes of bat development, sensory systems, and specializations related to flight and diet. The introduction notes that bats have rapid forelimb development, ear morphologies relating to echolocation, and other enhanced senses that allow them to exploit niches in virtually every part of the world. See the full study at PubMed.

The ecomorphology of bats, which links their physical form to their ecological roles, reveals how different species have adapted to different diets and habitats. Insectivorous bats tend to have fast, agile flight suited to chasing prey in open air or among vegetation. Fruit bats have broader wings that allow slower, more maneuverable flight through forest canopies. Nectar-feeding bats have elongated snouts and tongues for accessing flowers.

Comparing Bats with Gliding Mammals

Flying Squirrels

Flying squirrels are rodents that have a fur-covered membrane, called the patagium, stretching between their forelimbs and hindlimbs on each side of the body. When they spread their limbs, this membrane forms a gliding surface. Flying squirrels can control their direction and speed to some degree by adjusting the tension on the membrane and using their tail as a rudder, but they cannot generate lift or climb while in the air.

The key difference from bats is that flying squirrels do not flap their wings. They launch from a high point, glide downward, and land on a lower surface. To glide again, they must climb back to a high position. This limits their ability to move through open areas and makes them dependent on forested habitats with tall trees.

Colugos and Other Gliding Mammals

Colugos, also called flying lemurs, are not true lemurs and are not closely related to bats. They have a large gliding membrane that extends from the neck to the fingertips, toes, and tail, allowing them to glide considerable distances between trees. Other gliding mammals include certain marsupials, such as sugar gliders, and some rodents.

None of these animals can achieve powered flight. Their gliding ability is an adaptation for moving efficiently through forest canopies without descending to the ground, where they would be vulnerable to predators. The distinction between gliding and powered flight is fundamental and explains why bats are unique among mammals.

Evolutionary Implications

The research published in PeerJ on the origin of bat flight provides evidence that glider-like postcranial morphology precedes a bat-like morphology adapted to powered flight. The study proposes an adaptive landscape based on limb length and width optimal trends derived from modeling analyses. This supports the hypothesis that bats evolved from gliding ancestors, with intermediate forms showing limb proportions between those of non-gliding arborealists and modern bats. See the full study at PubMed.

This evolutionary pathway makes sense from a functional perspective. A gliding ancestor would already have elongated forelimbs and a membrane between the limbs. Natural selection favoring longer forelimbs and more controlled membrane movement could gradually lead to flapping flight. The transition would require coordinated changes in bone structure, muscle mass, and sensory systems.

Flight Performance and Aerodynamics

Airframe Design Comparisons

The flight performance of bats differs from that of birds in several important ways. A comparative study published in Bioinspiration and Biomimetics examines airframe design and flight performance in birds and bats. The study compares the aerodynamic characteristics of the two groups, including wing shape, wing loading, and flight efficiency. See the study at PubMed.

Bat wings are generally more flexible and can change shape more dramatically than bird wings. This allows bats to achieve high maneuverability at low speeds, which is useful for navigating cluttered environments and capturing agile prey. However, the flexible membrane wing is less efficient for sustained high-speed flight compared to the rigid, feathered wing of birds.

Maneuverability and Agility

The combination of flexible wings, rapid sensory feedback, and precise motor control gives bats exceptional maneuverability. Research on the somatosensory substrates of flight control in bats shows that the wing is innervated by sensory neurons that report airflow and touch, and that cortical neurons encode these inputs with sparse activity patterns. This system allows bats to make rapid adjustments to their wing movements in response to changing conditions. See the full study at PubMed.

Bats can perform tight turns, sudden stops, and rapid dives that would be impossible for most birds. They can also hover, which is essential for nectar-feeding species that must remain stationary while extending their tongues into flowers.

Hibernation and Seasonal Adaptations

Hibernation Patterns in Bats

Many bat species in temperate regions hibernate during winter when insect prey is unavailable. Research published in the Journal of Comparative Physiology B examined hibernation patterns of individual big brown bats (Eptesicus fuscus) overwintering in rock crevices that are smaller, drier, and less thermally stable than most known cave hibernacula. The study found that bats were insensitive to changes in hibernacula microclimate while torpid and that the probability of arousal from torpor remained under circadian influence. Flight appears to be an important winter activity that may expedite the benefits of euthermic periods and allow for short, physiologically effective arousals. See the full study at PubMed.

This research demonstrates that bats have flexible hibernation strategies that depend on local conditions. Bats hibernating in rock crevices exhibit different patterns than conspecifics hibernating in buildings and caves, showing that these animals can adapt their behavior to available roosting sites.

Energy Management During Torpor

During torpor, bats lower their body temperature and metabolic rate to conserve energy. The study of big brown bats in rock crevices calculated that individuals spend most of their energy on maintaining a torpid body temperature a few degrees above the range of ambient temperatures during steady-state torpor, instead of during arousals as is typical of other small mammalian hibernators. This finding has implications for understanding how bats survive winter with limited energy stores.

Circadian Rhythms and Activity Patterns

The Biological Clock in Bats

Bats have circadian timing systems that regulate their activity patterns. Research published in Frontiers in Neuroanatomy examined the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) in the flat-faced fruit-eating bat (Artibeus planirostris), a species endemic to South America. Unlike other species of phyllostomid bats, this species has its peak of activity 5 hours after sunset. The study mapped retinal projections and examined the cytoarchitecture of these nuclei, finding that the SCN contains vasopressin and vasoactive intestinal polypeptide neurons with neuropeptide Y, serotonin, and glutamic acid decarboxylase immunopositive fibers and terminals. See the full study at PubMed.

The variation in activity timing among bat species reflects their adaptation to different ecological niches. Some bats emerge at dusk, others fly in the middle of the night, and a few are active during the day. The neural substrate underlying these rhythms is the subject of ongoing research.

Reproduction and Placental Adaptations

Unique Features of Bat Pregnancy

Bats have reproductive strategies that are unusual among small mammals. Research published in Cell Reports on the Jamaican fruit bat placenta describes prolonged gestation relative to other small species, high metabolic demands, and continual microbial exposure. The study used single-nucleus RNA sequencing and tissue-derived organoid models to define the cellular and molecular architecture of the placenta. See the full study at PubMed.

The study revealed diverse trophoblast, stromal, and immune populations with bat-specific transcriptional programs, including fibroblasts with hybrid adventitial and neuronal signatures and macrophages expressing pregnancy-associated molecules typically restricted to trophoblasts. Functional assays demonstrated that bat trophoblast organoids maintain high basal antiviral gene expression but limited inducibility following viral stimulation. This unique strategy of immune vigilance without inflammation at the maternal-fetal barrier may underpin reproductive success under physiological extremes.

Fetal Development

Research on the fetal anatomy and allantoic placenta of an African fruit bat (Epomops franqueti) provides additional information about bat reproduction. The study, published in the Nigerian Journal of Physiological Sciences, examines the fetal anatomy and placental structure in this species. See the study at Semantic Scholar.

Bats in Agricultural Landscapes

Habitat Use and Biodiversity

Bats are important components of agricultural ecosystems, providing pest control services by consuming large quantities of insects. Research on bird and mammal diversity in agricultural landscapes of the Brazilian Atlantic Forest provides context for understanding how bats and other mammals respond to human-modified environments. The study notes that only 31% of the land in this biome remains as native forest, with most of the biome transformed by human activities, primarily for pasture and agriculture. See the study at Environmental Evidence.

Understanding which bat species persist in agricultural landscapes and how they use different habitat elements can inform conservation planning. Maintaining native vegetation adjacent to agricultural fields provides roosting and foraging habitat for bats, which in turn can benefit farmers through natural pest suppression.

Conservation Monitoring

Monitoring bat populations is essential for conservation, but conventional surveys are often limited by incomplete spatial coverage, high costs, and infrequent updates. Research published in Animals evaluated the potential of long-term, curated mass-media records to support biodiversity knowledge by analyzing a Chinese television program based mainly on infrared camera-trap footage collected across protected areas. The study documented 118 mammal species, including 42 nationally protected and 52 IUCN-threatened species. See the study at MDPI.

This research demonstrates that curated monitoring footage can recover broad-scale biodiversity patterns, although inherent taxonomic and spatial biases necessitate cautious interpretation. For bats specifically, acoustic monitoring and mist-netting remain the primary survey methods, but emerging technologies may supplement these approaches.

Common Misconceptions About Bats

Are Flying Squirrels Flying Mammals?

Flying squirrels are often described as flying mammals, but this is inaccurate. They are gliding mammals that can only descend from higher to lower positions. The distinction matters for understanding the biology of these animals and for appreciating the unique status of bats as the only mammals with powered flight.

Are All Bats Nocturnal?

Most bat species are nocturnal, but some are active during the day, particularly on islands where there are fewer predators. The flat-faced fruit-eating bat studied in the Frontiers in Neuroanatomy research has its peak of activity 5 hours after sunset, which is later than many other phyllostomid bats. See the study at PubMed.

Do All Bats Echolocate?

Not all bats echolocate. Pteropodids, also known as flying foxes or fruit bats, lack laryngeal echolocation and rely primarily on vision and smell to find food. The research on caudal auricular muscles in the greater short-nosed fruit bat examined a pteropodid and found that its ear muscle arrangement differs from that of echolocating bats. See the study at PubMed.

Practical Assessment Steps for Identifying Bats

When observing animals in flight, use these steps to determine whether you are seeing a bat or a gliding mammal:

1. Observe the flight pattern. Bats flap their wings continuously and can climb, turn, and hover. Gliding mammals descend in a relatively straight line without flapping.
2. Note the time of day. Bats are most active at dusk and during the night. Gliding mammals such as flying squirrels are also nocturnal but can sometimes be seen during the day.
3. Examine the wing shape if possible. Bat wings are long and narrow with visible finger bones supporting the membrane. Gliding membranes are broader and do not have finger bones.
4. Listen for echolocation calls. Many bats emit high-frequency calls that can be detected with a bat detector. Gliding mammals do not echolocate.
5. Consider the habitat. Bats can be found in a wide range of habitats, from forests to open fields to urban areas. Gliding mammals are typically restricted to forested areas with tall trees.

Records and Measurements for Bat Observation

For researchers and students documenting bat observations, maintain these records:

Common Failure Patterns in Bat Observation

Several common errors occur when people attempt to identify bats and understand their biology:

1. Confusing gliding mammals with bats. Flying squirrels and colugos are frequently misidentified as bats because they move through the air. The absence of flapping is the key distinguishing feature.
2. Assuming all bats echolocate. Fruit bats rely on vision and smell, and some species have large eyes adapted for night vision.
3. Believing bats are rodents. Bats belong to the order Chiroptera and are not closely related to rodents.
4. Underestimating the metabolic demands of flight. The high energy cost of powered flight shapes nearly every aspect of bat biology, from their diet to their reproductive strategies.
5. Overlooking the sensory complexity of bat wings. The wing membrane is beyond a passive airfoil but a highly innervated sensory organ that provides critical feedback for flight control.

Limitations of Current Knowledge

Despite decades of research, several aspects of bat biology remain poorly understood. The origin of bat flight is still not fully understood due to an uninformative fossil record, as noted in the PeerJ study on the origin of flight in bats. The evolutionary transition from gliding to powered flight is supported by comparative evidence, but the specific developmental and genetic mechanisms remain to be clarified.

Research on bat placentation and immune function is revealing unique adaptations, but the implications for human health and disease transmission require further study. The hypothesis that flight drives viral diversity in bats, proposed in the Emerging Infectious Diseases study, remains speculative and requires additional testing.

Safety and Regulatory Context

Bats are wild animals and should be observed from a distance. Do not handle bats, as they may carry diseases, including rabies. If you find a bat in your home or workplace, contact local wildlife authorities for guidance on safe removal.

In many jurisdictions, bats are protected by law, and disturbing roosts or colonies may be illegal. Before undertaking any activity that could affect bats, consult local regulations and seek professional advice.

Professional Escalation Criteria

Consult a wildlife biologist, veterinarian, or public health professional in these situations:

1. You find a bat in a living space where people or pets may have been exposed.
2. You observe a bat that appears sick, injured, or behaving abnormally during daylight hours.
3. You discover a large bat colony in a building and need guidance on exclusion or management.
4. You are planning activities that could disturb known bat roosts, such as tree removal or building renovation.
5. You need assistance identifying a bat species for research or conservation purposes.

Frequently Asked Questions

Why are bats the only mammals that can fly?

Bats are the only mammals capable of powered flight because they are the only mammals with the anatomical adaptations necessary for flapping flight. These adaptations include elongated forelimb bones that support a wing membrane, a keeled sternum for attachment of powerful flight muscles, and a highly mobile shoulder joint. Research published in PeerJ confirms that bats have correspondingly specialized body plans, particularly in their limb morphology, that are unique among mammals. See the study at PubMed.

What is the difference between a bat and a flying squirrel?

The main difference is that bats achieve powered flight by flapping their wings, while flying squirrels glide by descending from a high point with their limbs spread to stretch a membrane between their body and limbs. Flying squirrels cannot generate lift or climb while in the air, so they must return to a high position to glide again. Bats can fly from any position and can climb, turn, hover, and maintain level flight.

Are bats mammals?

Yes, bats are mammals. They belong to the order Chiroptera and share all the defining characteristics of mammals, including having hair or fur, producing milk to feed their young, being warm-blooded, and giving birth to live young. Bats are the only mammals capable of powered flight, as confirmed by research published in PeerJ. See the study at PubMed.

Do all bats use echolocation?

No, not all bats echolocate. Pteropodids, also known as flying foxes or fruit bats, lack laryngeal echolocation and rely primarily on vision and smell to locate food. Research on the greater short-nosed fruit bat examined the ear muscles of a pteropodid and found that its muscle arrangement differs from that of echolocating bats. See the study at PubMed.

How do bats fly in the dark?

Bats use echolocation to navigate and hunt in the dark. They emit high-frequency sounds and listen to the echoes that return from objects in their environment. Research published in Sensors describes how bats exhibit rapid adaptations in flight trajectory, sonar beam aim, and echolocation signal design to track moving targets. See the study at PubMed.

Why do bats hang upside down?

Bats hang upside down because their hindlimbs are adapted for hanging instead of for walking or running. This posture allows them to take off easily by dropping into flight, which is important because they cannot launch into the air from the ground. The hindlimb structure of bats is part of their specialized body plan for powered flight.

Are bats dangerous to humans?

Bats are wild animals and should be treated with respect and caution. They may carry diseases, including rabies, and should never be handled. However, bats are not aggressive toward humans and play important ecological roles, including insect control and pollination. If you find a bat in your living space, contact local wildlife authorities for guidance.

How long do bats live?

Bat lifespans vary by species, but many bats live significantly longer than other mammals of similar size. Some species can live for 20 to 30 years in the wild. Their longevity is thought to be related to their ability to enter torpor and hibernation, which reduces metabolic stress, and to their unique immune adaptations that allow them to coexist with viruses.

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References and Further Reading

• NCBI Literature Resources. National Center for Biotechnology Information.
• PubMed. National Library of Medicine.
• Gliding toward an understanding of the origin of flight in bats.. PeerJ, 2024.
• How the pterosaur got its wings.. Biological reviews of the Cambridge Philosophical Society, 2015.
• Cellular and immune adaptations at the maternal-fetal interface in bats.. Cell reports, 2025.
• Bat flight and zoonotic viruses.. Emerging infectious diseases, 2014.
• Ecomorphology and sensory biology of bats.. Anatomical record (Hoboken, N.J. : 2007), 2023.
• Adaptive Echolocation and Flight Behaviors in Bats Can Inspire Technology Innovations for Sonar Tracking and Interception.. Sensors (Basel, Switzerland), 2020.
• Physiological and behavioural adaptations by big brown bats hibernating in dry rock crevices.. Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 2024.
• Somatosensory substrates of flight control in bats.. Cell reports, 2015.
• Bird and mammal diversity in agricultural landscapes and adjacent natural vegetation of the Brazilian Atlantic Forest: a systematic map.. 2026.
• Beyond Social Media: Curated Monitoring Footage as a Biodiversity Information Source for Conservation.. 2026.
• Anatomy and homology of the caudal auricular muscles in greater short-nosed fruit bat (Cynopterus sphinx). Journal of Veterinary Medical Science, 2023.
• The Foetal Anatomy and Allantoic Placenta of An African Fruit Bat (Epomops franqueti).. Nigerian Journal of Physiological Sciences, 2020.
• The Suprachiasmatic Nucleus and the Intergeniculate Leaflet of the Flat-Faced Fruit-Eating Bat (Artibeus planirostris): Retinal Projections and Neurochemical Anatomy. Frontiers in Neuroanatomy, 2018.
• Bird or bat: Comparing airframe design and flight performance. Bioinspiration and Biomimetics, 2009.

This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.