How Swifts, Swallows and Sparrows Nested in Indian Buildings

The common swift (Apus apus) does not land on the ground by choice. Its legs are so short and its wings so long that touching down anywhere except a vertical surface is a trap it cannot escape from. For centuries, the deep overhangs of Indian havelis, the ventilation gaps in brick kilns, and the hollow spaces beneath old clay roof tiles gave it exactly what it needed: a narrow slot at height, sheltered from rain, with a clear drop for take-off. The swift did not adapt to buildings. It adopted them as the next available cliff face.

Barn swallows (Hirundo rustica) are more sociable about it. They need a horizontal surface above them and an open interior below, a rafter, a beam, a ledge just inside a doorway. Their nest is a cup of mud pellets and dry grass, pressed together in hundreds of trips from the nearest puddle or stream bank. A single nest weighs almost nothing but represents three to five days of constant labour. Old railway waiting rooms, temple corridors, cattle sheds, and the open ground floors of traditional courtyard houses gave them that geometry without asking anything in return.


The house sparrow (Passer domesticus) is the least particular of the three and so the most instructive. It does not need a specific shape, it needs a gap. A missing brick, a broken soffit, a space behind a wooden sign, the hollow interior of a rolled-up chik blind. Research published by the Bombay Natural History Society has tracked a measurable decline in house sparrow populations in Indian cities over the past two decades, and the leading structural explanation is not cats or noise or food scarcity. It is the disappearance of cavities. Glass-and-steel facades, sealed RCC construction, and the replacement of old wooden-framed windows with aluminium shutters have removed the sparrow's primary nesting resource from the urban fabric.





The architectural features that supported nesting were not designed for birds. They were the byproduct of how buildings were made before the mid-twentieth century. Lime mortar erodes unevenly and leaves pockets. Clay tiles sit on battens with air gaps between them. Wooden beams shrink and pull away from masonry walls. Jali screens let air through and birds in. Projecting chajjas, the deep horizontal sun-shades over windows and doors common in Rajasthani and Gujarati vernacular architecture, created sheltered ledges that swallows and sparrows found irresistible.

The courtyard house compounded the effect. An open central space meant birds could enter, nest under the first-floor overhang, and exit without navigating a closed room. The presence of a water source, the household well, the washing stone, within the same structure meant everything a nesting bird needed was within fifty metres. Swallows nesting in a Jodhpur haveli in the 1970s would have had mud from the courtyard, insects drawn to the stored grain, and a clear flight path out through the main gate. That combination no longer exists in most Indian cities.

All three species show strong nest-site fidelity. Swifts return to the same crevice year after year, sometimes across generations; a pair that nests in a particular roof gap will attempt to return to that exact spot the following monsoon. Swallows reuse and repair old nests rather than building new ones when they can. Sparrows, being year-round residents rather than migrants, defend a cavity across multiple breeding seasons.

This fidelity is an evolutionary advantage in stable environments, it removes the energy cost of scouting a new site each year. In a rapidly changing built environment, it becomes a liability. When a building is demolished, renovated with smooth renders, or reroofed with metal sheets, the birds return to a site that no longer exists. They do not immediately switch to a new location. They lose a breeding season, sometimes two, while they search. Population studies on urban swallows in Europe have shown that nest-site loss during renovation is one of the most direct causes of local decline, the birds are not killed, they simply cannot breed.



The shift to RCC construction eliminated cavities at scale. But the more immediate driver in Indian cities has been finishing. A building that might have offered nesting opportunities in its structural shell is sealed with external plaster, fitted with UPVC windows, and painted with weather-shield coatings that leave no texture for a mud nest to grip. The result is a surface that is, from a bird's perspective, biologically inert.

Reversal does not require building old buildings. Swift boxes, wooden nest boxes with a 28mm entrance slot, mounted under eaves at height, are used successfully in European cities and have been trialled by wildlife groups in Bengaluru and Pune. Swallow-friendly design requires only an open eave or a sheltered interior ledge and a mud source within walking distance. House sparrow nest boxes are available commercially and are among the easiest interventions to install on a balcony or terrace wall. The BNHS and the Nature Forever Society have both run urban sparrow monitoring programmes that accept citizen data, which means a nest box on a Mumbai apartment balcony can contribute to a real population dataset.

The deeper change is in awareness. A swallow nest on a rafter is not a mess to be knocked down before the monsoon ends. It is a structure built at a cost the bird cannot recover if the site is lost. Leaving it in place through the breeding season, typically March to July for the first brood, costs nothing and returns the nest for use the following year.