Abstract
Many animals use sounds produced by conspecifics for mate identification. Female insects and anuran amphibians, for instance, use acoustic cues to localize, orient toward and approach conspecific males prior to mating. Here we present a novel technique that utilizes multiple, distributed sound-indication devices and a miniature LED backpack to visualize and record the nocturnal phonotactic approach of females of the Australian orange-eyed tree frog (Litoria chloris) both in a laboratory arena and in the animal’s natural habitat. Continuous high-definition digital recording of the LED coordinates provides automatic tracking of the female’s position, and the illumination patterns of the sound-indication devices allow us to discriminate multiple sound sources including loudspeakers broadcasting calls as well as calls emitted by individual male frogs. This innovative methodology is widely applicable for the study of phonotaxis and spatial structures of acoustically communicating nocturnal animals.
Highlights
Nocturnal animals use sounds for a variety of purposes
This study demonstrates that phonotaxis of female frogs of L. chloris can be visualized using a miniature light emitting diode (LED) backpack and sound-indication devices both in a laboratory arena and in the animals’ natural habitat
The light on the backpack mounted on a female allows automatic tracking of her position (Figs 2a and 3a), and the illumination patterns of the sound-indication devices allow us to discriminate the timing of sound sources such as loudspeakers and calling males (Figs 2b and 3d)
Summary
Nocturnal animals use sounds for a variety of purposes. Bats emit ultrasounds to identify surrounding objects such as prey and obstacles[1]; barn owls localize moving prey with a high spatial resolution by analyzing interaural time and level differences of incoming sounds[2, 3]; crepuscular deer species vocalize for anti-predator purposes as well as for territory maintenance[4]. The Firefly unit consists of a miniature microphone and a light emitting diode (LED) that is illuminated when detecting nearby sounds Dozens of these devices were deployed at a natural breeding site of the Japanese tree frog (Hyla japonica). We propose a novel technique for visualizing phonotaxis of nocturnal animals by combining the Firefly system with a tracking technique using a miniature LED backpack (Fig. 1b). With this system, we were able to visualize the movement of females of the Australian orange-eyed tree frog (Litoria chloris) towards conspecific males. The technique is relatively inexpensive and deployable for the study of phonotaxis in nocturnal animals such as anurans, making it a substantial methodological advancement for the field
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