- A study published in Urban Ecosystems journal in 2022 investigated sympatric house sparrow and tree sparrow populations in Guwahati and impact of electromagnetic radiation (EMR) on abundance and habitat usage.
- The study observed commercial and residential areas in the city and found that while ecological factors largely influenced populations, with increasing urbanisation negatively impacting tree sparrows, both species were neutral to electromagnetic radiation.
- Scientists are now pushing for long-term studies on effects of EMR on sparrow fledglings on human settlement in urban environment, as these are yet to be studied intensively.
A systematic field study in Guwahati found that electromagnetic radiation (EMR) has no impact on two species of sparrows – house sparrows and tree sparrows – in terms of their abundance and how they interact with their urbanising habitats in Guwahati.
However, the analysis – carried out in 45 temporal and 168 spatial locations had their limitations, according to study author Anukul Nath from Wildlife Institute of India. A majority of the analysis was based on laboratory investigations on chickens (Gallus domesticus) and Japanese quail (Coturnix coturnix subsp. japonica). The remaining was carried out on the field, five instances of which revealed the possible impact of radiofrequency EMR on wild birds (house sparrow, great tit, blue tit, and white stork) with regards to their occupancy, abundance, breeding density, reproduction, and species composition. No part of the study considered other environmental variables that could also influence the habitat use of these species.
The fall of the sparrow
The house sparrow (Passer domesticus) was one of the most ‘successful’ urban birds, occupying two-thirds of the world’s surface. However, recent years have witnessed a decline in their populations across many parts of the world. Among the various causes hypothesised by the researchers from different parts of the globe – that have a direct and indirect impact – are lack of nesting sites due to rapid urbanisation, unsustainable loss of green cover, excessive use of pesticides, lack of traditional granaries, avian malaria, air pollution, and possible link with increasing electromagnetic radiation emitted from cell phone towers.
House sparrows usually thrive in an urban environment, where EMR is comparatively higher than wild, undisturbed habitats; this may allow sparrows to act as a useful biological indicator for detecting effects of radiation. Nath hypothesized that the species may not be able to tolerate EMR levels above a certain limit. While there are no studies that particularly look at this threshold limit, some studies in laboratory conditions found that more than 194 volt/metre of EMR intensity can raise heat which may be harmful to living beings.
“Small organisms are especially vulnerable as they possess thinner skulls, which may facilitate radiation penetration into the brain,” Nath says.
Between 2013 and 2015, the authors visited 45 locations on 10 occasions and collected data on the populations of house sparrows, tree sparrows, along with other associated urban birdlife: house crow, feral pigeon, common myna, jungle myna, spotted dove and Asian pied starling.
Simultaneously, the authors measured EMR for each location, selecting plausible ecological variables relevant to the ecology of both the sparrow species.
“The sparrows were found to be influenced by complex ‘ecological’ variables, e.g., distance to the nearest market place, number of food shops, number of rolling shutters in shops, distance to nearest green patch, amount of green cover, plant diversity, and spread of built-up area,” Nath says.
According to the study authors, the magnitude and impacts of such microhabitat variables may differ depending on needs that arise from the life history traits of the two sparrow species. Findings from the spatial and temporal scales revealed that these variables significantly influenced the way sparrows engaged with their habitat within Guwahati.
Owing to the growing demands for telecommunications and cellular network services, EMR levels are at an all-time high, and only continue to increase.
While EMR itself may not be an accurate indicator, Nath says that urbanisation trends were found to be influential in limiting the abundance of sparrows in Guwahati. The study estimated around 400,000 sparrows in total, including both species (about 253,615 to 357,454 of these are house sparrows). Interestingly, he noted that house sparrows were more commonly seen within urbanised areas, compared to areas with low settlement densities located far from the urban core. In contrast, tree sparrows were more scattered and rarely found in crowded areas. There was found to be a wide spatial overlap in residential areas adjacent to hillocks. In the urban setup of Guwahati, house sparrow had quadratic response to the degree of urbanisation – which means, initially house sparrow abundance was found to increase with urbanisation, however, when urbanisation reached the peak, sparrows tend to decline.
Both species had a tendency to avoid areas where urbanisation was extremely high, where natural vegetation was completely absent and top soil was paved over. Despite these differences, the habitat requirements of both species were found to be similar, with some overlaps.
An uncertain future for fledglings
The study authors stress on the vitality of long-term studies to monitor fledgling success of urban avifauna, having been unable to investigate potential impacts of EMR on fledglings. Only a tenth of the nest boxes placed by the authors in various strategic locations were occupied by sparrows for nesting. These were reported to host an average clutch size of 4.3 eggs, 84% of which hatched and 76% of these chicks fledged, resulting in an average of 3.3 chicks per nest.
EMR in these sites ranged from 3.7-5.2 volt per metre (V/m). While the authors did not find critical observable impacts on the reproductive success of house sparrows, they mention that long-term studies will be crucial in deepening existing knowledge, especially under the influence of other ecological variables.
Read more: It takes a village to save the sparrow
Rajah Jayapal, Senior Principal Scientist at the Sálim Ali Centre for Ornithology and Natural History (SACON), who was not associated with the study, told Mongabay-India: “It has been long suspected that EMR from telecommunication towers causes decline in house sparrow populations mediated through either high mortality of fledglings or low hatching success. Though some initial studies from Europe found some evidence to that effect, further studies with more rigorous experimental design fail to find any strong correlation. However, this remains strongly etched in media and public perception.”
Jayapal went on to reiterate what Nath’s study concluded – that EMR did not seem to possess a significant correlation with the densities of house and tree sparrows. “This particular study by Nath et al from the surroundings of Guwahati in Assam is perhaps the first systematic field study in India on the issue. A takeaway from this study is that we should focus more on urban ecological planning, providing more open green spaces so that sparrows and other birds can thrive amidst humans.”
While EMR doesn’t seem to affect house sparrows and tree sparrows, the authors cannot say the same for other species. According to them, exposure to prolonged EMR could be a serious concern for bees, fruit flies, frogs, birds, bats and even humans.
Nath adds however, that long-term studies of such exposures have been inconclusive and limited. Scientific communities have probed the extent of non-thermal exposure to low-intensity electromagnetic radiation, which is thought to have an adverse effect on health, reproduction, and behaviour of humans and other organisms.
Banner image: A sparrow roosting site in an urban environment. Photo by Anukul Nath.
