The Symphony and Cacophony of Sound – Their Role in Wildlife Management

As tourism booms in our wildlife reserves the places are becoming increasingly noisy. This is affecting the health and behavioral pattern of the wild animals. Animals depend on auditory cues to avoid predators, obtain food, and communicate. Auditory systems of some animals are very prone to physical damage from high decibel noise. Animal species that have evolved to take advantage of the quietest conditions in nature are the worst hit. Some human induced sound characteristics have been associated with suppression of the immune system and increased levels of stress-related hormones in animals. Research has demonstrated in unequivocal terms that human-induced noise pollution is one of many factors contributing to the decline of wildlife.

 In India no serious research has so far been done on the effects of extraneous human made noise on wildlife. Even in western countries field research on effects of noise pollution is sparse. But they have obtained excellent data from labs which is enough to keep the alarm bells ringing. In a study published in April edition of the scientific journal Trends in Ecology and Evolution, researchers in Colorado said that anthropogenic noise pollution affects wildlife around the world. They specifically mention the case of Colorado’s dwindling greater sage grouse. Human-created noise is interfering with the ability of male grouse to make their low-pitched mating calls audible to females.

The four ways in which wildlife is affected by sound are

         1) Hearing loss that results when the noise levels is 85 db or greater;

         2) Masking. Masking is the inability to hear important environmental cues and animal signals due to extraneous noise.

        3) Physiological effects, such as increased heart rate and respiration and associated stress reaction

       4) Abandonment of territory and lost reproduction associated with increased noise pollution.

 I am enumerating below some examples that should make us sit up and take notice.

An exposure to a an average 85 db of noise for 8 months in Rhesus Monkeys in the lab have shown 30% increase in blood pressure.

Research on mice has shown that when exposed to 82-85 db of noise they become very susceptible to disease. Their ability to negotiate mazes goes down considerably. 40-100% resorption of embryos and 66% reduction in fetal weight was also reported.

Dr Mac Arthur has clearly demonstrated that energy which might otherwise be devoted to reproduction, will be expended in escape and through higher levels of arousal sustained afterwards.

Noise is making Great tits (Parsus major) to sing at higher frequencies. In their natural environment birds must be able to distinguish their own songs and those of other species against the backdrop of background noise. Calls play cardinal role in the isolation of species, pair bond formation, pre-copulatory display and territorial defense

Female grey tree frogs (Hyla chrysoscelis) exposed to the sounds of passing traffic take longer to locate and find calling males. Calls of European tree frogs (Hyla arborea) have gone down alarmingly in recent years.

Dr Clifford G Rice who has done extensive research on Nilgiri tahr says the impact environmental disturbances on a tahr population through reduced reproduction could exceed that of direct mortality.

Studies of Dr Bunnell et al and Dr Gladwin have very clearly shown that when certain bird species are flushed from nests in response to noise, eggs are broken and young are exposed to injury and predators.

In many areas we have been pushing ecotourism unmindful of long term effects of our inroads in to the pristine habitat of the denizens of the wild. So much hype has been created in the name of ecotourism. Sure ecotourism rakes in money for the tour operators and in some cases the local communities. But let us not forget that this goose that lays golden eggs has to be nurtured with a long term perspective and has to remain a sustainable proposition.

Yes, we have the danger signals. It is time we called a spade a spade and acted to rein in unbridled tourism in wildlife reserves. The symphony of natural sounds in our wildlife reserves is an important natural resource that is very critical to the ecological communities.   Understanding the role of sound and acoustics in wildlife reserves is becoming increasingly germane in their management.    

Long-term effects from medium to low level noise intrusion need much more study, with emphasis on threatened and endangered species