How many sparrows are there in a city of million people? Understanding the population of sympatric sparrows in the urban gradient of a tropical city in Southeast Asia

In cities, species have to endure severe biotic and abiotic changes in their surroundings, along with various anthropogenic pressures. In recent years, urban dwellers have declined throughout the world, including the most successful urban adapters‒ House Sparrow and Tree Sparrow. We studied how the population and habitat use of sparrows varied at different urban habitats (city outskirts, followed by residential and highly crowded commercial zones) of Guwahati, India. We carried out point counts using distance sampling to estimate the density of sparrows. We found that sparrows were largely associated with complex urban structures, and the density of sparrows significantly differed between species amongst the habitat. House Sparrow density was three-fold of Tree Sparrow, and the occurrence of both the species was highest at mid-level of urbanization. Tree sparrow had low density compared to House Sparrow in areas where urbanization peaked. Unlike Tree Sparrow, the habitat-specific detection for House Sparrow did not vary significantly. The detectability of Tree Sparrow was higher in residential buildings. The Manly Selectivity ratio for the preference and avoidance of different habitats showed that House Sparrows occupied commercial areas and a combination of commercial-residential sectors more than available and avoided areas with a low level of urbanization (city outskirts). Tree sparrows significantly preferred human habitation dominated by residential houses. We estimated around four hundred thousand sparrows (House Sparrow: 253,615‒357,454; Tree Sparrow: 32,882‒163,533) in Guwahati. The present study creates a baseline information for the sparrow population and habitat use in Guwahati City, and provides emphasis for maintaining (mid-level urbanized) areas where both the species are abundant.