VOCALIZATION PATTERNS AND SOCIAL STRUCTURE IN BAT COLONIES UNDER URBAN NOISE PRESSURE

Abstract

Bats rely on sound to locate food, navigate as well as maintain a group.  But, increased machnoise in the urban areas may be interfering with their natural speech habits and even social systems.  The paper investigates the impact of noise in urban areas on bats and their hearing and colony organisation. With full-spectrum ultrasonic detectors, thermal imaging, and spatial network analysis we monitored six colony sites in cities and their surroundings.  Sound pressure levels (Leq) were determined using high accuracy sound meters.  We examined vocal parameters including call frequency changes (or translocation, 12), bandwidth and pulse interval of varying noise intensity.  To examine social organisation we employed the measures of roost mapping, emergence synchrony, and network centrality.  We, also, could interview ecologists and conservationists and examine the topics of our interviews. When the noise was severe, the urban colonies expressed markedly different vocalisation patterns where the dominant frequencies increased on average of 4.6 kHz.  The bandwidths had decreased and pulse rates had increased which shows the signs of compensatory behaviour.  Social cohesion decreased in noisy environments, and this was demonstrated by a decreased amount of people clustering up, an increased distance among members and reduced synchronous emergence.  Statistical modelling indicated that considerable relationships existed between Leq, 8f, and lower social structure indicators.  These trends were confirmed by the qualitative results and the emphasis was on the long-term results of noise pollution on the environment. The pressure of noise in urban areas is so high that it becomes difficult for bats to communicate with one another and also to manage their own social lives, and all this may influence the reproduction capabilities of these animals, as well as their ability to orientate themselves and maintain their numbers over the lifetime. Noise Area and Acoustic Refugia: In order to make the urban animals survive, it cannot be too much noise, instead, we need to apply noise zoning and acoustical refugia.