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The free-tailed bat (Tadarida brasiliensis) likely migrates from the southwestern USA and northern Mexico to the south of Mexico to spend the winter in the Cueva San Francisco (CSF), which is the southernmost known roost of the species. In this study, we examined colony size and composition of the free-tailed bats at the CSF for two annual cycles to know if these parameters fluctuate throughout the year and whether these fluctuations indicate that the CSF is a winter roost. From February 2018 to November 2019, we conducted monthly observations and captured bats with a mist net of 12 × 2.6 m to determine sex, age, reproductive status, and relative abundance. The duration of the emergence flight (DEF) was also recorded. We detected significant fluctuations in colony size that were caused by the movement of pregnant females in spring, lactating and post-lactating females and males in summer, and by females and males in autumn and winter. The CSF was occupied all year-round by females and males. Our results indicate that the cave is a winter roost for females and males, a transitional roost for pregnant females that form their maternity colony elsewhere in summer, and a temporary roost for males in summer. We suggest that the CSF is crucial for the conservation of the free-tailed bat.

Despite its peculiar distribution, the biology of the southernmost bat species in the world, the Chilean myotis (Myotis chiloensis), has garnered little attention so far. The species has a north-south distribution of c. 2800 km, mostly on the eastern side of the Andes mountain range. Use of extended torpor occurs in the southernmost portion of the range, putting the species at risk of bat white-nose syndrome, a fungal disease responsible for massive population declines in North American bats. Here, we examined how geographic distance and topology would be reflected in the population structure of M. chiloensis along the majority of its range using a double digestion RAD-seq method. We sampled 66 individuals across the species range and discovered pronounced isolation-by-distance. Furthermore, and surprisingly, we found higher degrees of heterozygosity in the southernmost populations compared to the north. A coalescence analysis revealed that our populations may still not have reached secondary contact after the Last Glacial Maximum. As for the potential spread of pathogens, such as the fungus causing WNS, connectivity among populations was noticeably low, especially between the southern hibernatory populations in the Magallanes and Tierra del Fuego, and more northerly populations. This suggests the probability of geographic spread of the disease from the north through bat-to-bat contact to susceptible populations is low. The study presents a rare case of defined population structure in a bat species and warrants further research on the underlying factors contributing to this. See the graphical abstract here. https://doi.org/10.25387/g3.12173385

espanolEl viento se esta utilizando cada vez mas como fuente de energia renovable en todo el mundo. Aunque las turbinas eolicas ayudan a reducir la emision de gases de efecto invernadero, no se pueden pasar por alto los costos que conllevan para la fauna salvaje. Hasta la fecha, los programas de seguimiento e investigacion se han centrado principalmente en el impacto de los parques eolicos en las aves, aunque se ha constatado que tambien afectan a los murcielagos. En este trabajo se compila informacion sobre la mortalidad del murcielago rabudo en los parques eolicos del sur de Espana y destacamos la necesidad de conocer mejor y evitar la mortalidad de murcielagos en un mundo donde la demanda de energias renovables no para de aumentar. EnglishWind is increasingly used as a renewable energy all around the world. Although wind turbines help reduce greenhouse gas emissions, the costs to wild -life cannot be overlooked. To date, monitoring programs and research have mainly focused on the impact of wind farms on birds but negative effects on bats have also reported. Here we compile information related to European free–tailed bat deaths at wind farms in southern Spain. In a world where the demand for renewable energy is rising we highlight the need to better understand and prevent bat fatalities.

A new record of the Midas free-tailed bat, Mops midas (Sundevall, 1843), from Saudi Arabia is presented. This new record is the northernmost occurrence point of this rare bat in Arabia (ca. 160 km NNW of the closest previous site) and also within its entire distribution range.

The Mediterranean Basin is a global biodiversity hotspot, hosting a number of native species belonging to families that are found almost exclusively in tropical climates. Yet, whether or not these taxa were able to survive in the Mediterranean region during the Quaternary climatic oscillations remains unknown. Focusing on the European free‐tailed bat (Tadarida teniotis), we aimed to (a) identify potential ancient populations and glacial refugia; (b) determine the post‐glacial colonization routes across the Mediterranean; and (c) evaluate current population structure and demography. Mitochondrial and nuclear markers were used to understand T. teniotis evolutionary and demographic history. We show that T. teniotis is likely restricted to the Western Palearctic, with mitochondrial phylogeny suggesting a split between an Anatolian/Middle East clade and a European clade. Nuclear data pointed to three genetic populations, one of which is an isolated and highly differentiated group in the Canary Islands, another distributed across Iberia, Morocco, and France, and a third stretching from Italy to the east, with admixture following a pattern of isolation by distance. Evolutionary and demographic reconstruction supports a pre‐Last Glacial Maximum (LGM) colonization of Italy and the Anatolian/Middle East, while the remaining populations were colonized from Italy after the Younger Dryas. We also found support for demographic expansion following the Iberian colonization. The results show that during the LGM T. teniotis persisted in Mediterranean refugia and has subsequently expanded to its current circum‐Mediterranean range. Our findings raise questions regarding the physiological and ecological traits that enabled species with tropical affinities to survive in colder climates.

Little is known about the natural history and distribution of the molossid bat Nyctinomops aurispinosus (Chiroptera, Molossidae) due to the rarity in which it is collected in fieldwork. In Brazil, this species is known for only nine localities, including the type-locality, 161 km from land on the coast of Cabo Sao Roque, state of Rio Grande do Norte, Brazil. Here we report a new record of N. aurispinosus for the municipality of Uberlândia, the second record of this species for the state of Minas Gerais in southeastern Brazil. We also present an updated distributional map for this molossid species in Brazil.

We present the first report on the occurrence of a free-tailed bat from Similipal Biosphere Reserve in Odisha, eastern India. Although the examined individual was a pup that was only a few days old and hence species identity could not be ascertained, the study provides important clues for a systematic survey to resolve the issue.

The Khao Chong Phran Non-hunting Area has the largest population of wrinkle-lipped free-tailed bats (Chaerephon plicatus) in Thailand. We examined monthly variations in sexual size dimorphism through measurements of forearm length and body mass during 2016. Bats were captured in each month at dawn and dusk. Individuals were sexed, aged, measured and marked before release. During the year, we caught 1,715 individuals. Of these, we used only adult, non-pregnant individuals (405 males and 538 females) for our analysis. Males had significantly larger forearm lengths and body masses than females. The body masses of both sexes peaked at the beginning and end of the rainy season, and bats captured at dawn were heavier than those netted at dusk. Seasonal fluctuations in body mass were correlated with monthly variation in rainfall; the positive correlation is likely explained by the greater insect abundance during wet months. The climate in western Thailand is expected to become warmer and drier, with likely negative effects on populations of this species due to reductions in insect food resources. Maintenance of this large population of C. plicatus in the study area will depend on concerted conservation efforts and further research focused on population dynamics, prey availability and foraging habitats.

Based on recent bat surveys in the Department of Madre de Dios, Peru, we present distribution records for Thyroptera wynneae Velazco et al., 2014 and Molossops temminckii (Burmeister, 1854), which extend the known distributions and represent the southernmost records of these species in Peru. We also present records of Molossus alvarezi González-Ruiz et al., 2011, which are the easternmost occurrences for this species in the country. Also included are new records of Eumops maurus (Thomas, 1901) and Molossus coibensis Allen, 1904 which fill existing gaps in the knowledge of the distribution of these species in the Neotropics.&nbsp

We found the four species of Nyctinomops Miller, 1902 living in sympatry in central Guatemala. All specimens were found dead under turbines of a wind farm. Nyctinomops femorosaccus (Merriam, 1889), was previously known from northern Mexico and southwestern United States, and this record extends its distribution at least 1150 km southward, representing the first record for Guatemala and Central America. Although N. aurispinosus (Peale, 1848) and N. macrotis (Gray, 1839) were already known from Central America (Honduras), and these are the first records for Guatemala.

The Mexican free-tailed bat, Tadarida brasiliensis, is a fast-flying bat that hunts by biosonar at high altitudes in open space. The auditory periphery and ascending auditory pathways have been described in great detail for this species, but nothing is yet known about its auditory cortex. Here we describe the topographical organization of response properties in the primary auditory cortex (AC) of the Mexican free-tailed bat with emphasis on the sensitivity for FM sweeps and echo-delay tuning. Responses of 716 units to pure tones and of 373 units to FM sweeps and FM–FM pairs were recorded extracellularly using multielectrode arrays in anesthetized bats. A general tonotopy was confirmed with low frequencies represented caudally and high frequencies represented rostrally. Characteristic frequencies (CF) ranged from 15 to 70 kHz, and fifty percent of CFs fell between 20 and 30 kHz, reflecting a hyper-representation of a bandwidth corresponding to search-phase echolocation pulses. Most units showed a stronger response to downward rather than upward FM sweeps and forty percent of the neurons interspersed throughout AC (150/371) showed echo-delay sensitivity to FM–FM pairs. Overall, the results illustrate that the free-tailed bat auditory cortex is organized similarly to that of other FM-type insectivorous bats.

We investigated a large colony of European free-tailed bats (Tadarida teniotis) in Spain, using a combination of capture-mark-recapture data and direct observations. Its social and reproductive organisation is complex and the mating system fits a “resource defence polygyny” model. In spring and autumn, aggressive interactions in flight, defence of roosts and mating songs of males to attract females occurred. According to our results, T. teniotis is organised in “harems” consisting of a dominant male and a variable number of females. In addition the sexual cycle displayed a bimodal reproductive pattern (this is unique and remarkable for European bats). The bimodal pattern coincided with peaks in food availability (moths) at high altitudes. Presumably, roost-guarding activities (patrolling, advertising…) make males less prone to move away (e.g. at higher altitudes and longer distances) from roosts, resulting in differences in prey selection and in altitudinal segregation between sexes. This provides a plausible explanation for the differences in diet (predation of more sedentary vs. high-flying migratory moths) between males and females that has been found in published studies.

Sredozemni repaš, Tadarida teniotis (Rafinesque, 1814) je vrsta slepog miša iz porodice Molossidae, rasprostranjena uglavnom na području Mediterana. Pripadnici ove vrste koriste skloništa u pukotinama teško dostupnih litica i stena, lete brzo i visoko iznad tla, i sposobni su za duge letove. Budući da je T. teniotis zabeležena u susednim državama i da u Srbiji postoje za nju pogodna staništa, prisustvo ove vrste na teritoriji Srbije je bilo očekivano. Na području zaštićenog prirodnog dobra Predeo izuzetnih odlika 'Vlasina' vršena je inventarizacija faune slepih miševa u periodu 2015-2017. godine. U veče 18. oktobra 2017. godine na lokalitetu Vlasina Stojkovićeva (42.691016o severne geografske širine, 22.373792o istočne geografske dužine, 1356 m n.v.) primenom metode ultrazvučne audiodetekcije definitivno je potvrđeno prisustvo vrste T. teniotis, što predstavlja njen prvi nalaz u Srbiji. Ovim je ukupan broj vrsta faune slepih miševa Srbije povećan na 31. Dalja istraživanja su neophodna kako bi se utvrdilo da li postoje skloništa ove vrste, da li se reprodukuje i/ili hibernira na teritoriji Srbije.

The Peale's free-tailed bat (Nyctinomops aurispinosus) is found in Sonora and Tamaulipas (Mexico) and in South America (Venezuela, Colombia, Peru, Bolivia, and Brazil) but there are no records from Central America. Known altitudinal range of this bat is from sea level to 3,150 m; most known records are from below 1,000 masl. We report the occurrence of Nyctinomops aurispinosus in Central America based on a recently dead male found in southern Honduras. The nearest localities where it has been reported are western Sonora and eastern Tamaulipas, Mexico. The specimen was found at 1,239 masl on December 5th, 2014 in a disturbed oak-pine forest used for cattle ranching with some human infrastructure recently built in the site. We have registered several other species of bats in this study site, including N. laticaudatus, Eumops underwoodi, four vespertilionids and three mormoopids, most of them difficult to catch by mist nets. We add a new bat species to the Honduras list which now stands at 108 species.

Harris County, Texas, is home to both species of North American night herons, black-crowned (Nycticorax nycticorax) and yellow-crowned (Nycticorax violacea). Both species are carnivorous, consuming a wide variety of vertebrates and invertebrates, although records of either species consuming bats have not been reported. During studies at a local colony of free-tailed bats living under the Waugh Bridge (Houston, Texas), significant feeding behavior observations of both herons were made. Both species were recorded foraging on this urban bat population, utilizing different methods for acquiring the bats as prey. Some of the behaviors are novel as well and are also discussed.

Mexican Free-tailed Bats (Tadarida brasiliensis mexicana) from a bridge colony in Big Bend Ranch State Park, Presidio County, Texas were followed over two natal seasons sand two winters. For the period of this study, the bridge was being utilized as a maternity roost with a number of the young of the summer overwintering in each of the two winters examined. The site also was used by nonreproductive adult males during spring and summer. Adult bats left the bridge roost by mid-to-late summer, leaving only young of the summer at the bridge to exploit roost and local resources through the fall and winter. Young of the summer being left at the maternity roost to overwinter is a novel behavior for T. b. mexicana. Sex-and age-specific segregation of bats is inferred within the bridge roost.

Otomops wroughtoni is an extremely rare molossid bat, known so far by a single breeding colony in southwestern India and two single individuals recorded in Meghalaya and Cambodia. We report here the discovery of three new roosts located in large karstic caves of the Jaintia Hills, in southeastern Meghalaya. Visual counts indicate that at least 90 individuals occupied these new roosts in February 2014, which doubles the known world population of this species. The new populations of Wroughton’s Free-tailed Bats from the Jaintia Hills have considerable value for the conservation of this elusive species. Although these bats are protected under national laws, their cave roosts and hunting habitats are subjected to severe and ongoing degradation. A protection plan that would include more extensive surveys and a strict conservation of these caves should be implemented rapidly to mitigate these threats.

Tadarida aegyptiaca (mean body mass 13.5 g) is a fast flying insectivorous bat that hunts in open areas for extended periods, covering extensive distances during its foraging bouts. Whole blood samples taken from the wing arteries were analysed for 2,3-diphosphoglyceric acid, oxygen affinity and pH. The mean oxygen affinity of T. aegyptiaca blood with a P50-value 38.3 mm Hg (5.1 kPa) is lower than that of similarsized bats but not as low as the P50-values of 48.5 mm Hg (6.4 kPa) in two mice species. This indicates that oxygen affinity of the blood in T. aegyptiaca and other bats is designed to facilitate both effective binding of oxygen with haemoglobin at the alveolar/blood capillary interface and oxygen offloading in the tissues. Haematocrits (54–60 %) and levels of 2,3 DPG (2.36–3.30 mM l–1) were higher, and blood pH (7.106–7.229) lower, than those reported for terrestrial species of a similar size, but within the range of values reported for other bats. We conclude that adequate delivery of oxygen to tissues with high metabolic demands during flight is facilitated primarily by an elevated haematocrit and a reduced blood pH in response to elevated levels of metabolic by-products such as 2,3-DPG (from the citrate acid cycle) and CO2 (leading to increased concentrations of H+ ions).Key words: oxygen affinity, haematocrit, 2,3-diphosphoglyceric acid, blood pH.

The present study reports the occurrence of Parakosa flexipes (Pinichpongse) (Chirodiscidae) for the first time in Brazil, along with its infection sites on Molossus rufus E. Geoffroy. Thirty-eight bats were caught using mist nets that were placed near a house at the Mars Center for Cocoa Science in the state of Bahia, of which 14 (37%) were parasitized by P. flexipes. Parakosa flexipes was observed parasitizing M. rufus on hairs that were evidently longer than others distributed over the bat's body, where up to three parasites could be spotted on a single hair.

We collected the skeleton of a big free-tailed bat (Nyctinomops macrotis) at a wind energy facility in Starr County, Texas. This is the first specimen record from the Lower Rio Grande Valley in southern Texas.

The echolocation calls of Tadarida teniotis were studied in an outdoor flight enclosure (captive individuals) and in the wild using single microphones or an array of four microphones. Calls were characterized by measures of 10 call variables. Comparison of individual calls recorded on four microphones arrayed in a tetrahedron with 1 m between each microphone revealed that all calls were not equally detectable by all microphones but that there were no significant differences in call features obtained from calls recorded on all four microphones. A comparison of 47 calls recorded by all four microphones showed no significant differences in the features of the four recordings of each call. Analysis of calls of five individuals flying individually in an outdoor flight cage revealed significant individual differences in call features. In the field, T. teniotis used long, narrowband search-phase calls, usually without harmonics. Analysis of 1876 search-phase echolocation calls of T. teniotis recorded in the field in Israel and Greece in 2002, 2005 and 2006 showed significant year-to-year and site-to-site differences in some call features. When flying in the presence of conspecifics, T. teniotis changed their echolocation calls. We found a range of different buzzes in the wild, and based on their structure we attempted to classify them as feeding and social buzzes. The features of individual calls comprising buzzes differed significantly among buzzes, and yet there were no consistent differences between what we classified as feeding and social buzzes.

Otomops madagascariensis is a large (24–27 g) molossid bat endemic to Madagascar. Unlike its congener O. martiensseni, in nearby mainland Africa, little is known about its ecology although it appears to roost only in caves. It is only known from a few sites in the west and occupies a small percentage of the available caves. We studied roosting colonies in seven vertical erosion domes in the roof of a cave in Parc National Tsingy de Bemaraha during July and October 2003. We also captured bats as they emerged from and returned to a roost cave in the south. Female bats examined in the west during October and in the south during November were pregnant. In the roosting colonies, one group contained 57 pregnant females and five adult males. Most other groups also consisted of both sexes but three male-only groups were encountered in October. Diet consisted mainly of Lepidoptera and Coleoptera and there was variation between sites and study locations in the contribution of these prey types. Otomops mada...

We present data on prenatal growth, development, and skeletal ossification for the Angolan free-tailed bat (Mops condylurus), a species distributed throughout sub-Saharan Africa. Specimens were measured for crown‐rump length (CRL), greatest length of the skull (GLS), forearm length, mass, and wing area. We cleared and differentially stained specimens for cartilage and bone to quantify pattern of skeletogenesis. Significant regressions for general growth trajectories were generated by plotting CRL and fetal mass against GLS. We quantified growth of the forearm, which showed a positive relationship with growth of the skull. Curiously, wing area was highly positively related to fetal mass, suggesting an ecomorphological relationship of wing loading and flight ability being established early in development in this species. Patterns of ossification in this species were more similar to those of phyllostomid and pteropodid bats than they were to vespertilionid bats, to which M. condylurus is apparently more closely related. In this paper, we provide the 1st published account of prenatal growth, development, and skeletal ossification for the Angolan free-tailed bat, Mops condylurus (Chiroptera: Molossidae). Understanding developmental patterns provides key insights into the evolution of form and function as well as the origins of key evolutionary innovations (Jablonka and Lamb 1998). Indeed, heterochronic shifts in developmental timing are in large part responsible for the evolutionary diversity of the vertebrate limb (Smith 2003).

It has been reported previously that in the inferior colliculus of the bat Molossus molossus, neuronal duration tuning is ambiguous because the tuning type of the neurons dramatically changes with the sound level. In the present study, duration tuning was examined in the auditory cortex of M. molossus to describe if it is as ambiguous as the collicular tuning. From a population of 174 cortical 104 (60 %) neurons did not show duration selectivity (all-pass). Around 5 % (9 units) responded preferentially to stimuli having longer durations showing long-pass duration response functions, 35 (20 %) responded to a narrow range of stimulus durations showing band-pass duration response functions, 24 (14 %) responded most strongly to short stimulus durations showing short-pass duration response functions and two neurons (1 %) responded best to two different stimulus durations showing a two-peaked duration–response function. The majority of neurons showing short- (16 out of 24) and band-pass (24 out 35) selectivity displayed “O-shaped” duration response areas. In contrast to the inferior colliculus, duration tuning in the auditory cortex of M. molossus appears level tolerant. That is, the type of duration selectivity and the stimulus duration eliciting the maximum response were unaffected by changing sound level.

The distribution of the European Free-tailed Bat Tadarida teniotis extends from southern Europe and northern Africa to Myanmar. In India it is known only from Bihar, West Bengal and Kerala. This study records the species for the first time in the western Himalayan state of Uttarakhand. Echolocation calls were found to be higher in frequency and shorter in duration than reported in previous studies. Extensive acoustic surveys are recommended to assess the distribution of this species in India.

In this paper we report the discovery of a colony of Wrinkle-lipped Free-tailed Bat Chaerephon plicatus for the first time in Sri Lanka, and a record of this species after a lapse of 20 years. C. plicatus has been recorded twice previously, in 1935 and 1997, but a roosting colony has not been recorded before. In May 2016, a colony containing about 300 C. plicatus was observed in a vertical cleft of the rock supporting Sigiriya fortress, a popular historical tourist destination. Four bats were captured during their evening emergence using mist nets. Recording of echolocation calls showed them to be similar to those previously documented for this species in being narrow bandwidth with shallow frequency modulation and low peak frequency (24.9–30.3 kHz), with average call duration of 7.7milliseconds (ms). The forearm length range (45.2–49.1 mm) of captured specimens corresponds to the specimen recorded in 1997 in Sri Lanka and with those recorded in Vietnam and Myanmar. The discovery of a colony of C. plicatus in Sri Lanka provides a basis for future studies of the biology and taxonomy of this species.

We studied roost microclimates, thermal preferences and temperature-related variation in body temperatures and flight abilities of M. condylurus from three roosts in man-made structures in South Af...

The reproductive pattern in male Angolan free-tailed bats Tadarida (Mops) condylura was studied at two localities in the Eastern Transvaal during the period 1989-1991. Males displayed a nine-month breeding season extending from June to February. Following testicular recrudescence in early June, spermatogenic activity displayed two periods of peak activity in August/early September and November/early December. Although testes became involuted in March, baseline spermatogenic activity was maintained and tests never regressed to prepubertal conditions. Leydig cell morphology closely followed spermatogenic activity, with the diameter of Leydig cell nuclei displaying a concomitant seasonal pattern.

One hundred and ninety five specimens of free tailed bat (Tadarida brasiliensis) obtained from two regions of Chile were analized to determine parasite infection. From those specimens the endoparasites identified were: Trematoda: Acanthatrium lunatum, Limatuoides limatulus and Paralecithodendrium carlsbadensis; Cestoda: Vampirolepis sp.; Nematoda: Nochtia pilosus and Anoplostrongylus paradoxus. The ectoparasites identified were Chiroptonyssus robustipes, Ewingnana inaequalis and Notoedres lasionycteris all of them are acari species. Even thought the bat specimens are from the same species on both survey sites, the results differ for each site when the parasite species identified are compared.

The Angolan free-tailed bat (Mops condylurus) uses roosts that often exceed 40 degrees C, an ambient temperature (Ta) that is lethal to many microchiropterans. We measured the physiological responses of this species at Ta's from 15 degrees to 45 degrees C. Torpor was commonly employed during the day at the lower Ta, but the bats generally remained euthermic at night, with a mean body temperature (Tb) of 35.2 degrees C. Metabolic rate reflected the pattern of Tb, increasing with falling Ta at night but decreasing during the day. Metabolic rate and evaporative losses were lower in torpid than in euthermic bats. Body temperature increased at each Ta35 degrees C and was 43 degrees C at Ta of 45 degrees C. At Ta of 40 degrees C bats increased dry thermal conductance and evaporative heat loss compared to lower Ta. At 45 degrees C dry thermal conductance was lower than at 40 degrees C and evaporative heat loss was 132% of metabolic heat production. At high Ta there was only a slight increase in metabolic rate despite the employment of evaporative cooling mechanisms and an increase in Tb. Collectively our results suggest that M. condylurus is well suited to tolerate high Ta, and this may enable it to exploit thermally challenging roost sites and to colonise habitats and exploit food sources where less stressful roosts are limiting.

Numerous studies have documented that bats are unusually long-lived for small mammals (Tuttle & Stevenson, 1982; Jurgens & Prothero, 1987 and references therein). In the absence of data on overall population dynamics, longevity can be an important demographic parameter for interspecific comparisons (Tuttle & Stevenson, 1982). Here, we present the first data on the longevity of a small population of Tadarida teniotis .

Grothe, Benedikt, Thomas J. Park, and Gerd Schuller. Medial superior olive in the free-tailed bat: response to pure tones and amplitude-modulated tones. J. Neurophysiol. 77: 1553–1565, 1997. In mammals with good low-frequency hearing and a moderate to large interear distance, neurons in the medial superior olive (MSO) are sensitive to interaural time differences (ITDs). Most small mammals, however, do not hear low frequencies and do not experience significant ITDs, suggesting that their MSOs participate in functions other than ITD coding. In one bat species, the mustached bat, the MSO is a functionally monaural nucleus, acting as a low-pass filter for the rate of sinusoidally amplitude-modulated (SAM) stimuli. We investigated whether the more typical binaural MSO of the Mexican free-tailed bat also acts as an SAM filter. We recorded from 60 MSO neurons with their best frequencies covering the entire audiogram of this bat. The majority revealed bilateral excitation and indirect evidence for inhibition (EI/EI; 55%). The remaining neurons exhibited reduced inputs, mostly lacking ipsilateral inputs (28% I/EI; 12% O/EI; 5% EI/O). Most neurons (64%) responded with a phasic discharge to pure tones; the remaining neurons exhibited an additional sustained component. For stimulation with pure tones, two thirds of the cells exhibited monotonic rate-level functions for ipsilateral, contralateral, or binaural stimulation. In contrast, nearly all neurons exhibited nonmonotonic rate-level functions when tested with SAM stimuli. Eighty-eight percent of the neurons responded with a phase-locked discharge to SAM stimuli at low modulation rates and exhibited low-pass filter characteristics in the modulation transfer function (MTF) for ipsilateral, contralateral, and binaural stimulation. The MTF for ipsilateral stimulation usually did not match that for contralateral stimulation. Introducing interaural intensity differences (IIDs) changed the MTF in unpredictable ways. We also found that responses to SAMs depended on the carrier frequency. In some neurons we measured the time course of the ipsilaterally and contralaterally evoked inhibition by presenting brief frequency-modulated sweeps at different ITDs. The duration and timing of inhibition could be related to the SAM cutoff for binaural stimulation. We conclude that the response of the MSO in the free-tailed bat is created by a complex interaction of inhibition and excitation. The different time constants of inputs create a low-pass filter for SAM stimuli. However, the MSO output is an integrated response to the temporal structure of a stimulus as well as its azimuthal position, i.e., IIDs. There are no in vivo results concerning filter characteristics in a “classical” MSO, but our data confirm an earlier speculation about this interdependence based on data accessed from a gerbil brain slice preparation.