3.2.1 Bands

Researchers have been banding bats for over a century (Ellison 2008). Initially, bird bands were used on bats' legs, but injuries and scar tissue made reading them difficult (Griffin 1945). Forearm banding was introduced in 1940 (Trapido and Crowe 1946) and became standard. All nine researchers surveyed in North America by Hitchcock (1957) reported that aluminium bird bands (e.g., Figure 2a) caused injuries in most bats, and that some bands embedded into wing tissue were chewed and rendered illegible. Consequently, Hitchcock (1957) recommended rounded corner bands and upturned lipped bands to reduce injuries. Herreid et al. (1960) confirmed that rounded, lipped bands decreased embedded injuries in Tadarida brasiliensis (6% vs. 37% for bird bands), though 2-year injury rates were similar for the two band types. They suggested further modifications, leading to the adoption of the omega-shaped lipped bands (Figure 2b,c), now the standard for bat-specific bands, though coloured plastic bands are also used (Ellison 2008; García-Rawlins et al. 2021).

Since the early 1960s, varying efficacy issues and injuries related to bands have been documented across numerous studies. For example, Rousettus leschenaultii and Megaderma spp. either chewed off their bands (unspecified type) or died from infection (Brosset 1962). Corynorhinus townsendii banded with 2.8- or 3.0-mm diameter lipped-alloy bands experienced an 11.8% injury rate from 17 days to 1 year after banding (Pierson and Fellers 1993). There was no severe damage during the first year after banding 199 Nyctalus noctula with aluminium-lipped bands from the U.K. Mammal Society (size not specified; Cranbrook et al. 1965). However, during the following 2 years, six individuals (4% of 143 recaptures) had perforated wings from bands, and four individuals (3% of recaptures) had embedded and chewed bands. Cranbrook et al. (1965) reasoned the aluminium bands were inferior for this large bat and switched to harder magnesium-alloy bands; subsequently, they noted only one of six bats was injured and none chewed the band. Seven per cent of recaptured Myotis macropus banded with metal lipped bands issued by the Australian Bird and Bat Banding Scheme (size not reported) had significant injuries, including perforation of the wing, while 2% of recaptured Myotis macropus had minor injuries such as abrasions (Law et al. 2020). In another study of Australian vespertilionids (Chalinolobus morio, Vespadelus darlingtonia, Vespadelus regulus, Vespadelus pumilus) captured 4–11 years post-banding, injury rates were < 1% for the same types of bands (Law et al. 2023). Considerably higher rates of major injuries (> 20%) have been reported in other studies. Major injuries (e.g., forearm swelling, lack of band movement, lesions, tissue growing around the band, damage to patagium) occurred in 20% of individuals in 14 of 17 species from five families (Megadermatidae, Rhinolophidae, Emballonuridae, Molossidae and Vespertilionidae) recaptured in Australia (Baker et al. 2001). However, some bats were banded with bird bands and some with bat bands (see below and Table S1) and recapture rates were low. Similarly, 22% of Perimyotis subflavus experienced injuries from 2.4-mm diameter aluminium-lipped bands ranging from scarring to punctured wings over a 6-year period, despite standardised application with banding pliers (Perea et al. 2024). Based on a 12-year dataset on injury rates of multiple species of free-ranging bats in north-eastern Spain, Lobato-Bailón et al. (2023) concluded that 2.5–4 mm diameter lipped aluminium–magnesium bands can cause serious health effects ranging from skin thinning to embedded bands (e.g., Figure 2d). Of 790 banded bats in this dataset, 55% exhibited skin lesions near the band, but injury rates ranged from no injuries in Nyctalus lasiopterus (n = 12) to 66% of 259 banded Pipistrellus pygmaeus (Table S1).

In addition to injury rates, some studies examined the effects of bands on body condition. The Scaled Mass Index (SMI) of Pipistrellus kuhlii banded with 2.4-mm aluminium alloy bands did not differ from PIT-tagged bats (Locatelli et al. 2019). Banded and uninjured Carollia perspicillata had a similar SMI to unmarked individuals, but females with more severe lesions had lower SMI, amounting to ~1 g or 5% of body mass (Mellado et al. 2022).

Species are affected differently by bands. Carollia perspicillata exhibited a high rate (54.1%) of chewing on aluminium bands (Fleming 1988), whereas Nyctalus noctula showed considerable variation in chewing, with some aluminium-lipped bands showing no evidence of chewing for 2 years and others damaged to the point of illegibility (Cranbrook et al. 1965). Chewing often makes bands unreadable and may also deform the band (Figure 2a), leading to injury. Excessive chewing might also cause tooth wear (Reynolds et al. 2025). Some species, such as Phyllostomids, seem particularly injury prone. Eleven (50%) Carollia perspicillata in a captive colony banded with 4.2-mm diameter lipped aluminium–magnesium bands developed injuries, and 18.2% of injuries were severe (Lobato-Bailón et al. 2023). However, bats in captivity may be in poor condition due to not adapting well to the feeding regime or stress and not tolerate bands as well as individuals in the wild (Kravchenko et al. 2023). Mellado et al. (2022) also found relatively high injury rates in Carollia perspicillata. Of 531 bats banded with 3-mm anodised lipped aluminium bands, 25% had minor injuries and 10% had more severe wounds (e.g., embedded bands and inflammation). In contrast, only 13 of 3403 (0.4%) of bands of recaptured Pipistrellus pipistrellus (total banded = 15,839) needed to be removed due to injuries (Sendor and Simon 2003).

Age may influence injury rates and chewing rates. Carollia perspicillata and Myotis lucifugus marked as juveniles had lower injury rates and chewed bands less than bats marked as adults (Mellado et al. 2022; Reynolds et al. 2025), suggesting juveniles are more tolerant of bands than adults.

Multiple studies have assessed the effects of various factors such as band type, size and application method. For example, bat bands caused fewer injuries in Miniopteris schreibersii and Myotis macropus than did bird bands, whereas bird bands caused fewer injuries in Chalinolobus gouldii, Kerivoula papuensis, Nyctophilus geoffroyi, Vespadelus darlingtoni, Vespadelus regulus and Vespadelus vulturnus (Baker et al. 2001, see Table S1). Plastic split-ring bands caused injury rates in 80% of Myotis lucifugus, whereas injury rates from No. 2 U.S. Fish and Wildlife bird bands and lipped aluminium bat bands were lower, 15.7% and 2.5%–5.9% (depending on size), respectively (Reynolds et al. 2025).

Band size also affects injury rates. Because band size effects differ among species, Eurobats (2003) made species-specific recommendations for band diameters, generally recommending larger bands for larger bats. This recommendation was corroborated by Vlaschenko (2012) based on 10 years of data on bats. Intraspecies variation in injury rates has been reported for several species where different diameter bands were applied and effects compared. While most of 377 Nyctalus leisleri (forearm length 35–48 mm; GBIF 2023) marked with alloy bands showed no injuries from bands (197 recaptures; 11.2% overall injury rate), rates of injury were 40% for 2.4-mm bands versus only 9.6% for 2.9-mm bands (Zambelli et al. 2009). Likewise, injury rates were higher when Rhinolophus euryale (forearm 43–51 mm, GBIF 2023) and Rhinolophus mehelyi (forearm 48–56 mm, GBIF 2023) were marked with 2.9-mm bands (17.4% and 61.2%, respectively) versus 3.5-mm bands (7.1% and 9.1%, respectively; Dietz et al. 2006). For the smaller Myotis lucifugus (forearm length: 33–41 mm, Fenton and Barclay 1980), injury rates are lower when 2.9-mm bands are used (2.5%) versus 4.2-mm bands (5.9%; Reynolds et al. 2025). Among recaptured Chalinolobus morio (35–42 mm, GBIF 2023), 5.3% exhibited minor injuries and 31.6% exhibited major injuries when marked with 2.5-mm (No. 1), lipped copper–nickel alloy bat bands and no injuries when marked with 3-mm bands of the same material (Baker et al. 2001). Neonatal Tadarida brasiliensis (forearm length: 42–46 mm, Wilkins 1989) marked with No. 1 and No. 2 U.S. Fish and Wildlife Service bands incurred soft tissue injuries, skeletal damage and abnormal development of the forearm and digits (Perry and Beckett 1966); smaller No. 1 bands caused more frequent and severe injuries, but improper band application led to injuries for bats marked with larger bands (i.e., when squeezed too tightly).

Banding techniques, such as the amount of pressure applied to the band, and use of pliers can influence injury rates and body condition. For example, bands (0.15 g, unspecified type, Centro Inanellamento Pipistrelli) applied on Rhinolophus ferrumequinum (13–34 g) with excessive pressure were associated with a measurable loss in body mass (1–2 g) after 1 year, whereas properly tightened bands caused no such mass loss (Dinale 1965). In a 41-week study of the effects of bands on free-ranging Pipistrellus nanus in Malawi, Happold and Happold (1998) found that the degree of band closure was important to injury rates. Most recaptured bats (66% of 447 recaptures of 75 individuals) banded with 2.2-mm alloy flanged bat bands had a free-moving band and were uninjured, but 11% had irritation or healed wounds, 11% had bands immobilised by healed wounds and 11% had an active wound and immobilised band. Happold and Happold (1998) concluded that applying incremental pressure with a finger and thumb so that the flanges just barely closed prevented the band from falling off and resulted in fewer wounds and immobilised bands than squeezing the band until the gap was nearly closed. Banding pliers (Figure 2c) designed to standardise band application and maintain the shape of the band were used to apply 2.9-mm lipped aluminium alloy bands to 1460 Myotis lucifugus and 8 Myotis septentrionalis (Hicks et al. 2013). Half of the bats were banded on both wings to examine retention rates. Only 7 (0.8%) of 701 recaptured bats exhibited an injury 8–13 months after original banding, four of which were related to the band slipping proximally. Retention rates were high (99%), although 6.4% of bands showed signs of chewing. The authors concluded that bands applied with pliers had no effect on survival.

3.2.2 Radio Transmitters and Proximity Sensors

Radio transmitters (including GPS tags) and proximity sensors are temporary marks useful for studies on movement, behaviour and other aspects of bat ecology. Radio transmitters (Figure 3a,b) were first used on bats in the 1960s, becoming more common after the late 1980s (Clerc et al. 2021); proximity sensors (Figure 3c) have only recently been used on bats (Ripperger et al. 2016). Device mass, attachment type (e.g., glue, suture or collar), location on the body and novelty are factors that contribute to how these marks affect bats and impact their behaviour. All studies reported on sublethal effects except for one. Three Nyctophilus gouldi were found dead 7 days after radio tagging (Threlfall et al. 2013). However, the cause of death is unknown and could have been due to other factors as all three bats had high endoparasite loads.

Mass is an important factor influencing flight dynamics, with additional mass affecting manoeuvrability and foraging ability, particularly in cluttered habitats (Aldridge and Brigham 1988). Based on radio tracking studies of fruit bats, Bradbury et al. (1979) suggested a 10% rule (i.e., that the mass of the transmitter be ≤ 10% of body mass). However, they suggested that smaller insectivorous bats may need a lighter load. Aldridge and Brigham (1988) tested the manoeuvrability of Myotis yumanensis with disks weighing 5%–33% of their body mass in an obstacle course consisting of vertical twine of varying intertwine distances. Bats without disks could negotiate significantly smaller intertwine distances, and intertwine distance was negatively associated with body mass and wing loading for bats with and without disks. Because manoeuvrability should be inversely proportional to body mass, the authors assumed that a 5% increase in body mass would result in a 5% decrease in manoeuvrability. Consequently, they suggested radio transmitters should be < 5% of body mass for bats weighing < 70 g and that they should only be used when prey is abundant, as foraging ability may be affected.

Adherence to the 5% recommendation varies widely across studies and the American Society of Mammalogists currently recommends using transmitters that weigh 5%–10% of an animal's body mass (Sikes and Animal Care and Use Committee of the American Society of Mammalogists 2016). While 98% of 148 studies reviewed by O'Mara et al. (2014) used transmitters < 10% of bats' body mass, only 51% of studies used tags that weighed < 5%. More recently, Meierhofer et al. (2025) found that 55% of published studies from 1999 to 2022 reported transmitter weights > 5% of bats' body mass. However, effects of transmitter mass on bats have rarely been tested. A meta-analysis of transmitter effects on Nyctalus noctula found that although most individuals lost mass after tagging, this was not related to the mass of the transmitter but instead to the duration of tag attachment and initial body mass (Kelling et al. 2024). However, emergence time was delayed and foraging duration increased with tag mass. Radio-tagged Sturnira lilium emerged from their roosts about 25 min later than untagged individuals (Fenton et al. 2000). In contrast, activity time and behaviour of Myotis evotis did not differ between radio-tagged and untagged individuals despite transmitters weighing 5.9%–8.9% of body mass (Chruszcz and Barclay 2003). Tag loading (transmitter mass/body mass) did not affect Plecotus auritus foraging distance or time spent within 0.5 km of the roost (Entwistle et al. 1996) nor foraging time for Myotis moluccarum (Barclay et al. 2000). Furthermore, GPS tags weighing as much as 14% of body mass did not affect the ability of Leptonycteris yerbabuenae to hover at flowers or time spent foraging, compared to bats with much lighter transmitters (3.3% of body mass; Goldshtein et al. 2020).

While transmitter or sensor mass is important, the distribution of that weight on the bat's body relative to the bat's centre of mass (COM) must also be considered (Katzner and Young 2024). Based on weight-balanced calculations for aviation, devices placed at COM have little impact on flight control or stability, but the farther the device is from the bat's COM, the greater the effect of device mass on the bat's ability to maintain flight control and stability. For example, a device weighing 3% of body mass could substantially impact Lasiurus cinereus' ability to maintain stability if it was placed on the hip or tail, and even a collar could affect flight. The authors conclude that the 5% threshold only holds if the device is placed at COM. However, it should be noted that these calculations do not consider the energetic costs of the additional weight of the devices.

Some studies tested the effect of transmitters on foraging success, behaviour, body condition and survival. Foraging success rates of Lasiurus cinereus carrying radio transmitters weighing 2.5%–3.7% of their body mass were similar to individuals without transmitters (Hickey 1992). However, Lasiurus cinereus are relatively large and usually forage in open areas; closed-space foragers may be more affected due to a need for greater manoeuvrability. Measures of condition (body mass or body condition index) did not differ between radio-tagged and untagged hibernating Myotis lucifugus after 55 days (Jonasson and Willis 2012), tagged and untagged Nyctalus noctula (Roeleke et al. 2016; Voigt et al. 2020), nor tagged and untagged Rhinolophus ferrumequinum (Park et al. 2000). Apparent survival and fitness of Eptesicus fuscus with radio transmitters weighing 2.6%–5.7% of their body mass (mean = 3.7%) did not differ significantly from untagged bats; 37 of 40 bats were alive 1 year after radio-tagging (Neubaum et al. 2005). Based on a meta-analysis of 12 studies and 17 estimates of transmitter impacts, Meierhofer et al. (2025) concluded that transmitters affect bat behaviour and body condition, but that the overall magnitude of the effects may be negligible.

Transmitter attachment method greatly affects the efficacy and effects of this mark. Radio transmitters can be attached using adhesives, sutures or via collars (Amelon et al. 2009; Castle et al. 2015). Non-toxic, surgical adhesives are commonly used to attach transmitters to bats' dorsa (Figure 3a), with retention averaging < 10 days (O'Mara et al. 2014), but retention varies greatly depending on adhesive type (Carter et al. 2009). Use of adhesives can result in hair loss which could affect bats' thermal capabilities, particularly during hibernation. Because temperate zone bats usually moult during late spring or summer, a bald spot created during late summer may last throughout winter hibernation. For example, all 31 Myotis daubentonii banded and radio-tagged after moult and recaptured the following season had bald spots (Rolfes et al. 2021). However, nine of 11 females recaptured were reproductive, suggesting limited fitness impacts. Kurta and Murray (2002) made similar observations of bald spots and signs of reproduction for two radio-tagged Myotis sodalis recaptured the next summer, while nine other tagged bats had no bald spot upon recapture. Adhesive and solder on wires may also add to the device's mass and should be considered in the weight ratio.

Transmitters attached via collars (Figure 3b) are more common for larger bats. Three transmitter collar designs were tested on Pteropus alecto, Pteropus vampyrus and Pteropus neohibernicus in the field and on Pteropus alecto, Pteropus scapulatus and Pteropus conspicillatus in captivity (Smith et al. 2011). Wild bats tolerated the collars well, as did all five captive Pteropus alecto fitted with a leather collar with sheepskin glued to the inner surface, although three had some reddening under the collar to day 9 but not through day 28. In a second captive trial, one of eight Pteropus scapulatus and two Pteropus conspicillatus did not tolerate the collar, and it was removed. For the remaining animals, adverse effects were only observed 8 weeks post-collaring when issues such as wet dermatitis and ulceration, slipping of the collar and suppurative dermatitis began to appear. Several collar designs were tested on two neotropical fruit bats (Artibeus jamaicensis and Uroderma bilobatum), Mollossus mollossus and the European vespertilionid Nyctalus noctula (O'Mara et al. 2014). Collars made from shoelaces and tied with degradable suture material were the most effective and degraded within approximately 30 days. These collars worked well on Artibeus jamaicensis, Uroderma bilobatum and Nyctalus noctula and extended the effective transmitter life by ~21 days for Nyctalus noctula compared to glue. However, half of the Mollossus molossus removed the collars or continually scratched at them.

Suturing transmitters to the dorsum has also been tested on Eptesicus fuscus and Lasiurus cinereus (Castle et al. 2015). No irritation was observed on two Eptesicus fuscus captured 11–12 days after attachment, but the fur was worn away for one Eptesicus fuscus recaptured 227 days later, and there was loose skin near the caudal end of the transmitter, but no bleeding, bruising or inflammation. Of several Lasiurus cinereus captured 2–26 days post attachment, one showed signs of chafing despite the tag still being fully attached. Two Lasiurus cinereus were recaptured 213–224 days post-attachment; one had no fur loss, skin or wing injury or infection, whereas the other individual's tag had rotated and was attached only at one corner, but there was no skin damage. The authors concluded that, overall, there were no conspicuous adverse effects of suturing transmitters onto bats.

Whatever attachment method, the presence of a novel item may affect individual and colony behaviour. This has been most closely examined in the case of proximity sensors (Figure 3c), which log the amount of time animals are within a user-determined distance from each other. Proximity sensors placed on Myotis myotis, a species that roosts in tight clusters, appeared to have no behavioural effect based on videos (Ripperger et al. 2016). Desmodus rotundus appeared to habituate relatively quickly to proximity sensors attached with skin-bonding adhesive, with self-grooming decreasing after the first hour and remaining steady (Kline et al. 2021). However, two bats removed the tags and increased grooming rates, suggesting that secure attachment is important.

3.2.3 PIT Tags

PIT tags are electromagnetic chips encoded with a unique number and injected under the skin (Figure 4a–c). When scanned with a specialised reader, the number is transmitted to a data logger and stored. PIT tags are a relatively new technology for bats; Barnard (1989) first published on their use in captive Eptesicus fuscus. While use is increasingly common, particularly over the last decade (Figure 5), the literature on effects is scant.

Possible effects of PIT tags include infection, irritation or hair loss at the injection site, movement of the tag within the body or undetected impacts to health. Body condition and recapture rates were similar for Myotis chiloensis and Tadarida brasiliensis with and without PIT tags in central Chile (Escobar et al. 2022). Similarly, body condition of Pipistrellus kuhlii PIT-tagged with 8.4-mm tags in southern Europe did not differ from banded individuals 2.6 years after marking (Locatelli et al. 2019). For Myotis daubentonii marked with 12-mm PIT tags and bands, there was no difference in recapture rate, body condition or reproductive success compared to individuals without PIT tags over a 3-year study (Rigby et al. 2012). No skin lesions were found in a captive colony of 21 Carollia perspicillata marked with 10-mm PIT tags, nor did video observations show evidence of discomfort or behavioural changes (Lobato-Bailón et al. 2023). These authors also reviewed data on recaptures of bats over a 12-year period in Catalonia, Spain, concluding that PIT tags did not cause undue impacts as no injuries were found for Myotis schreibersii (n = 116), Nyctalus lasiopterus (n = 5), Nyctalus leisleri (n = 79) or Pipistrellus pygmaeus (n = 246).

Efficacy of PIT tags, particularly their loss rate, is important in evaluating their use. Several studies used double marking methods to determine loss rates. Thirty-nine per cent of recaptured tagged and banded Myotis daubentonii either shed their PIT tags or the tags no longer scanned at the end of 3 years (Rigby et al. 2012). However, the success of PIT tagging increased as researchers gained more experience (e.g., correctly positioning tags). In contrast, PIT tag loss occurred in only 2.7% of 146 recaptured Chalinolobus gouldii (van Harten et al. 2021). The size of the PIT tag may affect efficacy. Smaller PIT tags (9-mm) implanted in Myotis lucifugus were detected significantly less often than 12-mm PIT tags, which the authors attributed to greater loss of the 9-mm tags and lower detectability by the antennas around each entrance to a roost in a building (Sandilands and Morningstar 2021).

Using adhesive to close the PIT tag injection site may cause hair loss. While fur loss was initially observed in 52 tagged Miniopterus orianae bassanii, 10 individuals captured 1–2 years after initial tagging had no external signs of tagging (van Harten et al. 2020). In three instances, thinner or atypically pigmented fur was observed at the injection site. All tags remained in their subcutaneous position between the scapulae, with no signs of tag migration. Hair loss < 10 mm in diameter was also observed in Chalinolobus gouldii at the injection site, which had received a small amount of glue, approximately 1 month after tagging, but usually regrew after 2 months (van Harten et al. 2021). However, one subadult female experienced more extensive hair and weight loss.

Many studies use permanent PIT tag readers within or outside roosts to monitor bat activity, social behaviour and survival (e.g., Ellison et al. 2007; Braun de Torrez et al. 2020; Waag et al. 2022; Rensel et al. 2023). Readers and antennas are arranged around entry and exit points of roosts and hibernacula to detect bats passing nearby (Figure 4d). Because bats need to be within ~50 cm of the antenna for the tag to be read, some access points may require extensive arrays. A novel item at a roost, no matter its size, may affect behaviour and could cause abandonment. However, no behavioural effects of PIT-tag antenna arrays were found for Myotis lucifugus, Eptesicus fuscus, Perimyotis subflavus and Myotis sodalis at two cave entrances during spring emergence (Britzke et al. 2014). The primary behaviour observed was circling, which is consistent with typical spring emergence behaviour. Contact with the reader, including landing, only accounted for 1%–3% of the behaviour during exiting. The authors concluded that careful placement of PIT tag antenna arrays does not limit bat movement and activity at cave entrances. However, site-specific configurations may be needed to limit behavioural impacts for some bat species (Adams and Ammerman 2015).

3.2.4 Collars

Multiple types of collars have been used, but ball-chain necklaces paired with coloured beads or bird or bat bands for individual identification are frequently used (Kunz and Weise 2009). Other collar types include plastic cable ties, coloured beads attached to nylon threads and colourless plastic tubes with identifying information inserted inside (Esbérard et al. 2011). Esbérard and Daemon (1999) did not observe significant issues with the plastic cable tie collars, including when applied on species with a gular gland, but Rodríguez-Posada and Santa-Sepúlveda (2013) observed deep skin abrasions in one Carollia brevicauda and one Sturnia ludovici. Kunz and Weise (2009) cautioned against using cable tie collars without vinyl tubing because bats can tighten them by chewing, resulting in injuries and choking. Injuries can also occur using ball-chain collars. Fifteen (2.2%) ball-chain necklaces were removed from 686 Carollia perspicillata recaptured over 2 years due to injuries (Fleming 1988). In contrast, no flesh injuries were observed in 411 Carollia perspicillata collared with ball-chain necklaces recaptured at least once (Mellado et al. 2022); however, 5% had alopecia which may or may not have been related to the collar. While collars may cause fewer injuries, collars may be lost more often than bands, resulting in biased estimates of survival (Mellado et al. 2022), and fading bead colour or rusting wire can occur (Alencar et al. 2020). Proper fit is essential to reduce both injury and loss rates. During an extensive study of the bats of Barro Colorado Island, thousands of bats were marked with ball-chain collars with low injury rates and a 6.6% loss rate (Handley et al. 1991). The authors suggest collars should be checked to assure that they are not too tight.

3.2.5 Marks to the Skin

Tattooing unique numbers or codes has been used on bats and was first reported by Griffin (1934). He used a 5-pointed tattoo needle, designed for marking rabbits, to apply numbers to the wings of Myotis lucifugus. The method proved unsatisfactory due to the lengthy application time, limited information that could be included in the mark and the need to recapture the individual in hand as the tattoo is generally on a body part not visible on a roosting bat. Bonaccorso and Smythe (1972) used a ‘tattoo outfit’ to punch numbers into the wing membrane (up to 5 digits applied at a time) and recaptured 12 of 91 tattooed Artibeus jamaicensis and 1 of 17 Saccopteryx bilineata with no injuries. Marks were legible after 32 days in wild-caught animals and 48 days in a captive animal. Patagium perforation was also tested in Myotis chiloensis and Tadarida brasiliensis and compared to hair-dye (Escobar et al. 2022). Maximum time that both types of marks were visible was similar (40–42 days), but a greater proportion of patagium perforation marks were visible at 40–42 days than hair dyes. A commercially available tattoo machine and black pigment, requiring marking time of < 20 s per bat, was used to mark 241 captive Rousettus aegyptiacus and 7771 wild-caught bats of 12 species in South Africa (Markotter et al. 2023). None of the captive Rousettus aegyptiacus showed signs of discomfort and 44 of the first captive bats to be tattooed still had legible tattoos after 927 days. Tattoos of some subadults and all neonates required reapplication due to fading. Of 439 recaptured wild bats over 256–2465 days, only 12 had illegible numbers, mostly on smaller species. The authors concluded that tattooing may be best for larger species, tattoos should be examined for legibility before release and training was essential.

Freeze-branding, that is, freezing the skin, destroys melanocytes in hair follicles and hair re-grows white. Sherwin et al. (2002) used branding irons (copper washer attached to a dowel) to freeze mark four species on their dorsa, observing them in captivity for up to 6 months prior to release. Although bats exhibited some discomfort during the processing, no long-lasting behavioural changes were observed. Four Corynorhinus townsendii were recaptured 3 years post-branding with still-readable marks. However, a limited number of symbols are available, and thus, this mark may not be suitable for large-scale studies.

Wing punches via sterilised biopsy tools create a short-term mark, as holes usually heal within 16–120 days, depending on punch size, location and species (Davis and Doster 1972; Faure et al. 2009; Weaver et al. 2009). Bleeding may occur if the punch is taken from an area of the wing with high vascularisation. Wounds created by wing punches may tear (Greville et al. 2018) and expand beyond the original punch size (Faure et al. 2009; Ceballos-Vasquez et al. 2015; Greville et al. 2018). The rate of wound healing can vary seasonally, with 8-mm diameter wounds healing faster during summer (4 weeks) than in winter (7 weeks; Ceballos-Vasquez et al. 2015). Biopsy punches in tail membranes of Eptesicus fuscus and Rousettus aegyptiacus healed significantly faster than those in the wings (Faure et al. 2009; Pollock et al. 2016; Greville et al. 2018). However, holes in tail membranes may put bats at risk of being entrapped on such objects as automobile antennas (Broders et al. 2013). It is not known if entrapment could also occur from holes in the wings.

3.2.6 Uncommonly Used Marking Methods

Other methods have been tested for short- and long-term marking of bats but are less common. Visible implant elastomers (VIE) are coloured polymers that are subcutaneously injected as a liquid into the forearm or leg of the animal, turning into a pliable solid. VIEs were tested on 650 bats of 22 species double marked with a collar in north-eastern Brazil (Alencar et al. 2020). The authors subsequently recaptured 54 individuals of seven species within 9 months, and the VIE was visible in all animals with no skin irritation or rejection of the VIE.

Small coloured and numbered disks such as bee tags or reflective tape glued to the backs or heads of bats have been used in hibernacula to track their movements (Kirkpatrick et al. 2019; Brown et al. 2025). Stickers have also been used on the bats' ear pinnae (Hooper and Amelon 2023). Tags can be applied to bats while they are in torpor without handling by using forceps or tweezers to place the tag on the bat. However, tactile disturbance, even just 15 s of rubbing, can cause a bat to increase its energy output and perhaps arouse (Speakman et al. 1991). Tag loss can also occur; Brown et al. (2025) recovered 4 of 39 tags (10.3%) on the floor of the hibernacula but 8 of 21 (38.1%) Perimyotis subflavus marked in the first month of the study retained their marks for at least 5 months, and 74.3% of bats that were marked for at least 3 months still had their tags at the end of the season.

Fluorescent powder is another marking method to study movements of bats both within hibernacula (Hoyt et al. 2018) and between maternity colonies and foraging areas (Medellin et al. 2018). The powder is dusted on the animal, and then, an ultraviolet light is used to either determine whether the animal has been dusted previously or to track trails of individual bats within a hibernaculum. To our knowledge, the effects of fluorescent powder on bats have not been tested but tests with deer mice (Peromyscus maniculatus; Stapp et al. 1994) showed that most (87%) had evidence of powder in their lungs, and 27% showed signs of pneumonia 3–27 days after marking. No mortality was observed, and the authors concluded that deleterious effects do not occur in most animals.

The collagen–elastin bundles in the wing, or wingerprints, are distinctive among individual bats and are another way to identify individuals (Amelon et al. 2017). This method requires no external marks or alteration of any body parts, although bat wings need to be photographed to obtain permanent records of individual wingerprints so that new and recaptured bats can be compared to known individuals. Thus, potential effects are limited to handling and time needed to photograph. This method has been used successfully to identify relatively small numbers of wild bats in flight cages and bat boxes (Fjelldal and van der Kooij 2024; Sørås et al. 2022, 2023). However, bats must be kept still long enough to get a good photograph, the wing must be held properly so that no parts are obscured, is time-consuming and would benefit from the development of pattern recognition algorithms that can automate identification (Amelon et al. 2017). Another technology, the p-Chip (p-Chip Corp.), consisting of a miniature laser-activated microtransponder semiconductor tag read with a red laser wand held in close proximity and containing a 9-digit alphanumeric code, has recently been tested in bats (Seheult et al. 2024). Thirty captive Eptesicus fuscus received chips dorsally over the right second metacarpal in the wing and dorsally over the right tibia. The wing location appears to be preferable due to shorter handling times, more consistent reading times, better visibility of the chip and zero instances of unreadable chips. Benefits over PIT tags include reduced costs and smaller needles, but they have more stringent proximity and operation requirements. These chips have also been tested in the field in 21 species in Peru and tags were detected 1–344 days after tagging with no signs of irritation at the injection site (Pellón et al. 2025).