Use of a Parabolic Microphone to Detect Hidden Subjects in Search and Rescue.
INTRODUCTION
This study compares a parabolic microphone to unaided hearing in detecting and comprehending hidden callers at ranges of 322 to 2510 m.


METHODS
Eight subjects were placed 322 to 2510 m away from a central listening point. The subjects were concealed, and their calling volume was calibrated. In random order, subjects were asked to call the name of a state for 5 minutes. Listeners with parabolic microphones and others with unaided hearing recorded the direction of the call (detection) and name of the state (comprehension).


RESULTS
The parabolic microphone was superior to unaided hearing in both detecting subjects and comprehending their calls, with an effect size (Cohen's d) of 1.58 for detection and 1.55 for comprehension. For each of the 8 hidden subjects, there were 24 detection attempts with the parabolic microphone and 54 to 60 attempts by unaided listeners. At the longer distances (1529-2510 m), the parabolic microphone was better at detecting callers (83% vs 51%; P<0.00001 by χ2) and comprehension (57% vs 12%; P<0.00001). At the shorter distances (322-1190 m), the parabolic microphone offered advantages in detection (100% vs 83%; P=0.000023) and comprehension (86% vs 51%; P<0.00001), although not as pronounced as at the longer distances.


CONCLUSIONS
Use of a 66-cm (26-inch) parabolic microphone significantly improved detection and comprehension of hidden calling subjects at distances between 322 and 2510 m when compared with unaided hearing. This study supports the use of a parabolic microphone in search and rescue to locate responsive subjects in favorable weather and terrain.
Techniques for Audio Recording Vocalizations of Tropical Birds
Audio recordings of tropical birds are important tools for biologists involved in the study, management, and conservation of birdlife; the ability to acoustically identify a species in a number of tropical habitats is essential. Recording method, equipment, and the condition of equipment can affect the accuracy and quantity of audio recordings collected. Suitability of currently available analog recording systems, emerging digital recording formats, and differing microphone designs for field work varies. This paper discusses essential and effective criteria that can be used to select a recording system based upon research goals and financial resources. To survey and study tropical birds, biologists increasingly recognize that it is essential to be able to identify the birds by their sounds and to have the skill to make audio recordings of their voices (Parker 1991). Although several papers have been written on making audio recordings of bird sounds for research (Gulledge 1976; Wickstrom 1982; Ranft 1991; Vielliard 1993), recent advances in recording technology, together with the specific requirements of the tropical researcher, warrant revisiting and updating the information presented in these publications. This paper presents the fundamental technical information required to master the operation of a field recording system and prepares the recordist for situations that may be encountered in the tropics. Resumen. Las grabaciones del sonido de aves tropicales son herramientas importantes para los biologos envueltos en el estudio, manejo y conservacion de las aves. La habilidad para identificar acusticamente a una especie en varios tipos de habitats tropicales es esencial. El metodo de grabacion, equipo y la condicion del equipo, pueden afectar la exactitud y cantidad de grabaciones coleccionadas. La conveniencia de los sistemas de grabacion analogos disponibles al presente, los formatos de grabaciones digitales actuales y los diferentes disenos de microfonos para trabajo de campo varian. Este articulo discute los criterios esenciales y efectivos que pueden ser utilizados para seleccionar un sistema de grabacion basado en las metas de investigacion y los recursos financieros disponibles. Para estudiar y hacer censos de aves tropicales, los biologos reconocen que es esencial poder identificar los pajaros por sus sonidos y tener las destrezas para hacer grabaciones de sus voces (Parker 1991). Aunque varias publicaciones sobre la preparacion de grabaciones de sonidos de aves han sido escritas para la investigacion (Gulledge 1976, Wickstrom 1982, Ranft 1991, Vielliard 1993), avances recientes en la tecnologia de grabacion, junto con los requerimientos especificos del investigador del tropico, ameritan revisar y poner al dia la informacion presentada en estas publicaciones. Este articulo presenta la informacion tecnica fundamental requerida para dominar la operacion de un sistema de grabaciones en el campo y prepara al grabador de sonidos de aves para situaciones que se pueden encontrar en los tropicos. THE IMPORTANCE OF RECORDING About 3,100 bird species (Ridgely and Tudor 1989), roughly a third of the world's bird species, occur on the continent of South America. Although much of the region's baseline natural history remains undocumented, the rate of habitat destruction is outpacing the ability of scientists to document and study these species and populations. The next decade offers a critical window of opportunity in which to document the voices of wildlife in the Neotropics before many disappear. Every researcher collecting sound recordings in this region can make a unique contribution to bird research and conservation (Kroodsma et al. 1996a). Relative to temperate latitude birds, the biology of tropical species is little known. Recordings of their voices provide important baseline data for research in the fields of avian systematics, behavior, and bioacoustics, and are essential to conservation initiatives as training and playback tools for surveys and censuses.
Great tits classify songs by individual voice characteristics
Abstract The first experimental evidence that birds are able to recognize the general voice characteristics of an individual's song repertoire is reported. Five captive male great tits, Parus major , were taught to discriminate between songs from the repertoires of two individuals. They were then tested with unfamiliar songs from the same two birds, which they were able to assign to the correct individual. These results provide a mechanism by which the well-known phenomenon of individual recognition by voice in birds can be achieved.