Variation in echolocation calls produced by Myotis velifer (Chiroptera: Vespertilionidae) during postnatal development

THERYA, 2019, Vol. 10 (1): 55-58 DOI: 10.12933/therya-19-656 ISSN 2007-3364 Variation in echolocation calls produced by Myotis velifer (Chiroptera: Vespertilionidae) during postnatal development Fabrizio Varela-Boydo1, Luis Gerardo Ávila-Torresagatón1, Areli Rizo-Aguilar1, and José Antonio Guerrero1* Facultad de Ciencias Biológicas, Universidad Autónoma del Estado de Morelos. Av. Universidad 1001, Cuernavaca, Morelos 62209, México. (FVB), (LGAT), (ARA), (JAG) * Corresponding author This work describes the echolocation pulses produced by Myotis velifer during postnatal development. The aim was to record the changes of these calls during the development of this bat species and investigate the underlying causes. Bat specimens were sampled in El Salitre cave, Morelos, Mexico, during May and June 2016, where juvenile bats were captured and sorted into five age classes. Forearm length was used as reference for offspring growth. Each juvenile bat was induced to fly and the echolocation calls produced were recorded using an ultrasound detector. Six quantitative characteristics of the echolocation pulses of each call were measured, which served as reference to explore the development of this system during growth through a linear regression. A steady increase in the frequency parameters associated with bat growth was observed, coupled with a decrease in the temporal parameters. The final pulse frequency was the only parameter that remained unchanged during postnatal growth. The major changes in the characteristics of echolocation pulses during postnatal growth in M. velifer follow the pattern observed in other species previously studied. These changes are likely related to the development of organs and muscles involved in the emission and reception of sound, and to the learning process involved in the use of this adaptation. En este trabajo realizamos grabaciones de los sonidos de ecolocalización de Myotis velifer con el propósito de describir los cambios que ocurren en las caractetrísticas de los pulsos durante su crecimiento postnatal. Realizamos muestreos en la cueva El Salitre, Morelos, México durante mayo y junio del 2016, donde se capturaron las crías y se clasificaron en cinco clases de edad. La longitud del antebrazo se utilizó como indicador del crecimiento de las crías. Fuera de la cueva, los individuos fueron liberados o forzados a intentar el vuelo para obtener las grabaciones de sus ultrasonidos utilizando un detector ultrasónico. Se midieron seis características cuantitativas de los pulsos de ecolocalización de cada individuo, las cuales sirvieron como referencia para estudiar el desarrollo de este sistema durante el crecimiento por medio de una regresión lineal. Los resultados mostraron un aumento progresivo en los parámetros de frecuencia asociado al crecimiento de las crías, así como una disminución en los parámetros temporales. La frecuencia final fue el único parámetro que no mostró modificaciones significativas durante el crecimiento postnatal. Los cambios notables en las características de los pulsos de ecolocalización durante el crecimiento posnatal de M. velifer siguen el patrón observado de especies anteriormente estudiadas. Es posible que estos cambios estén relacionados con el desarrollo de los órganos y músculos involucrados en la emisión y recepción del sonido y el aprendizaje del uso de esta adaptación. Key words: Age; bat; El Salitre cave; ontogeny; ultrasound. © 2019 Asociación Mexicana de Mastozoología, www.mastozoologiamexicana.org Introduction Most bats rely on the emission of echolocation calls for survival. In aerial insectivorous species, individuals must be capable of producing high-frequency sounds and process spatial information from the echoes produced in order to catch insects successfully during their early flights (Moss et al. 1997). Thus, sounds emitted during the first days after birth may be the precursors of echolocation behavior in adult bats (Moss et al. 1997; Zhang et al. 2005). In most cases, there is a correlation between postnatal development and the type of calls emitted by young bats (Brown and Grinnell 1980). In general, young bats emit long-duration, high-intensity and low-frequency pulses, relative to the sounds emitted by adults (Brown and Grinnell 1980; Rubsamen 1987; Monroy et al. 1995; Zhang et al. 2005; Liu et al. 2007). This differentiation of pulses between bats of different age might make it easier for juveniles to recognize adult individuals and follow them to suitable foraging grounds (Kazial et al. 2001). Works describing the development of vocalizations during postnatal growth, which include species of families Ves- pertilionidae (Moss et al. 1997; Zhang et al. 2005), Hipposideridae (Habersetzer and Marimuthu1986), Rhinolophidae (Rubsamen 1987; Liu et al. 2007), Noctilionidae (Brown et al. 1983), Mormoopidae (Veter et al. 2003) and Phyllostomidae (Carter et al. 2013) show a general pattern in the development of echolocation, consisting of a steady increase in frequencies and a reduction of the temporal patterns of pulses. In Mexico, there is virtually no research work addressing the relationship between postnatal growth and the development of echolocation. In this sense, the maternity colony of M. velifer that congregates each year at El Salitre cave, Morelos, offers an opportunity to describe in quantitative terms the pulses of echolocation calls produced by Myotis velifer (J. A. Allen, 1890), a species widely studied in United States but not in Mexico, during postnatal growth. Methods The study was conducted during June and July, 2016, in El Salitre cave, located in the municipality of Tlaltizapán, Morelos, Mexico (18° 45’ 00.3’’ N, 99° 11’ 23.3’’ W). Individuals (juvenile and adult bats) were captured with a hand net ECHOLOCATION IN MYOTIS VELIFER in the maternity colony that is established each year inside the cave, and were subsequently placed inside cotton cloth bags. After capture, the forearm length (FL) of each individual was measured with a CD-8’’CS digital caliper (Mitutoyo Corporation, Japan); additionally, each individual was sexed and sorted into one of 5 age categories (see Results), according to the ossification of phalanges, morphological traits and ability to fly. A flight simulation experiment was conducted outside of the cave, consisting in rising each individual bat up to a height of two meters, and then dropping it in front of a full-spectrum Echo Meter 3+ ultrasound detector (Wildlife Acoustics, Inc, USA.) set up to record at a sample rate 256 kHz/16-bit resolution and a 1x time expansion (real time). The detector was placed at two meters from the drop point with an inclination of 40º to ensure the capture and recording of echolocation pulses emitted by each bat released. To avoid potential injuries to individuals who were unable to fly, a soft surface was placed on the landing area. This technique has been used in previous studies to record vocalizations of juvenile (...truncated)