Natterer’s Bat (Myotis nattereri)

Natterer’s bat is a medium-sized insect-eating bat found across much of Europe, North Africa, and western Asia. It has a fringe of stiff hairs along the edge of its tail membrane that helps it sweep up insects. Roosting in tree holes, buildings, and caves, it hunts low over woodland, water, and pasture.

Natterer’s Bat (Myotis nattereri) is strictly nocturnal, emerging relatively late after dusk to begin foraging, with activity peaking in the hours after sunset and again before dawn. During daylight hours, individuals roost in tree hollows, crevices, bat boxes, caves, tunnels, and building spaces, showing a strong preference for wooded and semi-wooded habitats near water sources. Their emergence pattern is somewhat later than many other Myotis species, an adaptation thought to reduce predation risk from diurnal raptors and to align with peak insect activity.

Socially, this species forms maternity colonies of females numbering from a dozen to over a hundred individuals during the summer breeding season, while males tend to roost alone or in small bachelor groups. Communication relies heavily on echolocation calls (typically frequency-modulated, sweeping from around 110 kHz down to 20 kHz) used both for orientation and social contact, supplemented by low-frequency social calls and tactile interactions such as grooming within roosts. Colonies frequently switch roost sites within a local network, a behavior called roost-switching, which may reduce parasite loads and predation pressure.

Home ranges are moderate in size, generally extending a few kilometers from the roost, with individuals showing high fidelity to foraging areas and traditional hibernation sites used across multiple winters. Natterer’s Bat exhibits notable seasonal migration between summer roosts and underground hibernacula (caves, mines, cellars), sometimes traveling considerable distances. A distinctive adaptive behavior is its capacity for “gleaning” — picking prey directly from foliage, bark, and the ground rather than relying solely on aerial hawking, requiring slow, highly maneuverable flight enabled by broad wings and tail membrane.

As an insectivore, Natterer’s Bat employs a flexible foraging strategy combining aerial hawking with substantial gleaning behavior, using its broad wings, low-frequency echolocation, and acute hearing to detect prey rustling on leaves, bark, and ground litter. Diet studies show a strong reliance on non-flying arthropods including spiders, harvestmen, and caterpillars, alongside flying insects such as small moths, midges, craneflies, and beetles. This gleaning specialization distinguishes it from many other vesper bats and allows exploitation of prey inaccessible to purely aerial hunters, particularly within dense woodland understory.

Foraging typically occurs within closed-canopy forest, hedgerows, and along woodland edges, with individuals commuting along linear landscape features to reach productive hunting grounds. Seasonally, diet composition shifts according to insect emergence, with spring and early summer diets often dominated by emerging Diptera and spiders, while late summer sees increased consumption of moths and beetles as colonies build fat reserves for hibernation. Water dependency is significant; bats drink on the wing from ponds and streams, and proximity to water bodies strongly influences roost site selection and foraging success, especially during dry periods when insect abundance near water increases.

Breeding in Natterer’s Bat follows a promiscuous mating system with mating typically occurring in autumn at swarming sites near hibernacula, though sperm storage delays fertilization until after females emerge from hibernation in spring. Following ovulation and fertilization in spring, gestation lasts approximately 50 to 70 days, heavily influenced by ambient temperature and torpor use, which can slow embryonic development during cold spells. Females gather in maternity colonies segregated from males to give birth, usually producing a single pup per year, though twins are occasionally recorded.

Maternal care is intensive, with pups born naked and blind, relying entirely on the mother for warmth and nourishment via nursing for approximately four to six weeks until weaning, after which juveniles begin independent flight and foraging. Sexual maturity is typically reached by the following autumn or spring, around one year of age for females, while some males may take slightly longer. Longevity is notable for a small mammal, with individuals capable of living beyond 15 years in the wild, reflecting the generally slow life-history strategy characteristic of bats relative to their body size.

The primary ecological threats to Natterer’s Bat center on habitat loss and fragmentation, particularly the decline of mature woodland with suitable tree cavities and the removal of hedgerows and linear features used for commuting between roosts and foraging grounds. Agricultural intensification, pesticide use, and the resultant decline in insect populations pose a growing indirect threat by reducing prey availability. Disturbance of underground hibernacula through recreational caving, renovation, or sealing of old mines and tunnels can also disrupt overwintering populations, sometimes causing fatal arousal from torpor during energetically costly winter months.

Climate change presents an emerging concern, potentially altering hibernation timing, prey phenology, and roost microclimates, while natural predators such as owls, martens, and domestic cats present localized predation pressure, particularly at roost entrances. Currently classified as Least Concern by the IUCN due to its wide distribution across Europe to Central Asia and generally stable populations, the species nonetheless benefits from legal protections under agreements such as the Eurobats initiative and national wildlife legislation across its range, alongside active conservation measures including bat box schemes, woodland management for veteran trees, and protection of hibernation sites.

• Gleaning Specialist: Unlike most bats that hunt purely in flight, Natterer’s Bat frequently plucks spiders and insects directly off leaves, bark, and the ground using passive listening.
• Tail Membrane Basket: Its long tail membrane (uropatagium) can be curved forward to form a scoop, helping capture prey gleaned from surfaces mid-flight.
• Delayed Fertilization: Females store sperm from autumn mating through winter hibernation, only fertilizing eggs once spring conditions favor pup survival.
• Roost-Switching Behavior: Maternity colonies rotate between multiple roost sites every few days, likely to minimize ectoparasite buildup and predation risk.
• Exceptional Longevity: Despite weighing only 7–12 grams, wild individuals have been recorded living over 15 years, far exceeding typical mammalian lifespans of similar body size.
• Low-Frequency Social Calls: Beyond echolocation, colony members use distinct low-frequency calls for social cohesion, distinguishable from their steep frequency-modulated hunting calls.
• Wide Ecological Range: Found from the British Isles across continental Europe into Central Asia, this species tolerates a broad range of temperate woodland habitats, contributing to its Least Concern status.