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

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.