Introduction: What conservation problem or question does your study address?House Sparrow has been very much in news recently for its suspected population decline in various parts, largely based on anecdotal evidences. This study focuses on robust estimation of occupancy status of House sparrow in Delhi and its association with persisting habitats in an urban context. We also aim to explore the effect of electromagnetic radiations and competition with co-occurring urban bird species on its distribution.
Methods: What were the main research methods you used?Field studies were conducted during February to April 2012 & 2014 covering entire Delhi state. Presence/absence data for House Sparrow and other common urban species spotted on both sides of a line transect (1 km) from the 240 sub-grids comprising of 60 sampling grids, were recorded. Additionally, species abundance was also recorded to examine its effect on detectability. Using satellite imagery obtained from Global Land Cover Facility (Landsat ETM; 30 × 30 m resolution), closest to the period when the bird surveys were conducted, a land use cover map was generated which was used to obtain broad landscape categories in each grid. Using single season occupancy model in program presence, we modeled occupancy as a function of the extent of preferred habitat in a grid (% urban area) and averaged EMF values. We also used single season two species models to assess the co-occurrence level and effect of competition by other urban bird species.
Results: What are your most important results?The occupancy value (Ψ) of Sparrow is 0.74 ± 0.08 & 0.73 ± 0.12 for the year 2012 & 2014 respectively. Sparrow occupancy shows a positive association with its preferred habitat i.e, % urban area (β Hab = 1.58 ± 0.72) and a negative association with averaged EMF values (β EMF = -1.029 ± 0.19). Single season two species occupancy modeling reveals that the probability of occurrence of Sparrow given that some urban species like Common Myna and Rock Pigeon are absent is very high.
Discussion: What are your important discussion points and what is the relevance of your results to conservation (if any)?This study reveals that House Sparrow occupancy shows an increasing trend with the extent of % urban area while a strong negative association with averaged EMF values per grid. It lends support to the widespread speculation that high electromagnetic radiations from mobile towers and other sources may be responsible for the decline of House Sparrow population. Urban bird species like Common Myna and Rock pigeon are negatively impacting the occupancy of House Sparrow.