In the city, she lives on the edge. Beyond the standard expectation of motherhood, she must scout prime real estate for a home, provide warmth and care, and find optimum nutrition for the perpetually open offspring mouths.

Her partner, meanwhile, sticks to his brief: mostly standing guard and looking alert. In the bird universe, this is not bare minimum. This is “progressive” since the evolutionary role of most male birds does not go beyond mating. And since the house sparrow male does more than that, his “involvement” in parenting is lauded as participatory.

In a newly released paper, the researchers look at the difference in parental care between urban and rural house sparrows as well as between their sexes. They monitored 183 nest boxes set up by local NGOs at 17 locations in Tamil Nadu — urban Chennai and rural/urban sites around Arani in Tiruvannamalai district — for three years between in 2021 and 2024. They collected behavioural data on nest construction, incubation, guarding and food provisioning and looked at the reproductive success in terms of both hatching and fledging. The researchers also looked at how the risk of predation affected reproductive success.

Division of labour and urban demands

The study found that the classic division of labour existed between the sexes across urban and rural habitats. The total parental effort, however, was higher in urban nests, driven by females.

The lead author of the study Agnes Francila explains that consistent sex differences were observed across behaviours. “Males were primarily invested in guarding behaviour, while females took care of incubation. In food provisioning and nest construction, either both sexes contributed equally or females invested more,” she says.

Urban females took on more labour than rural females, investing a lot more time and energy in nest construction, incubation and food provisioning. Between the sexes, the study found that despite higher predation in the cities, the guarding time did not differ between urban and rural males for eggs or hatchlings.​

Since directly quantifying various environment factors contributing to behaviour change was difficult, the researchers used behaviour proxies for measurement. For instance, explains project lead and associate professor at IISER-Bhopal Vinita Gowda, time spent building a nest was treated as an indicator of effort in sourcing nesting material. If more time was spent building, that likely reflected greater energy expenditure. Similarly, the amount of time individuals spent away from the nest served as a proxy for time spent searching for food and collecting nesting materials.

“Using these proxy measurements in both urban and rural habitats, we compared patterns of behaviour. From this, we could identify which features were similar across habitats and which differed. The pattern that stood out was that males did not seem to change their behaviour very much between urban and rural environments. It was the females who appeared to be taking on the additional stress, investing more effort in urban habitats,” she says.

Increased labour without reproductive success

This additional labour, however, did not translate to better reproductive success. The study found that city females were laying just as many eggs as their rural counterparts but hatching success was significantly lower in urban habitats. In rural nests, about 62% of eggs hatched. In urban nests, that figure dropped to around 55%. The gap widened further at the fledging stage. Of the hatchlings in rural nests, approximately 63% survived to fledge. In urban nests, only about 41% made it that far.

This “urban penalty” is largely because predators are attacking the bird nests, according to the paper. Predation rates were dramatically higher in cities: Roughly 30 to 34% of urban nests were attacked by predators in the city while it was 9% in rural areas. Nest abandonment was another reason. In urban areas, between about 57 and 60% of nests were abandoned by the parents. In rural habitats, the incidents of parents abandoning the nest was much lower, at around 21%.

Senior Principal Scientist at SACON, Rajah Jayapal, notes that female investment in parental care is disproportionately higher in most bird species. “So, females are more stressed. Urban environments provide additional challenges that could lead to greater strain,” he says, adding that these results are consistent with findings from several previous studies.

He points to a reduction in dipteran insects, largely due to pollution in urban settings, as another stress factor for house sparrows. “They are granivorous, but the chicks need insects,” he explains. Nestlings also rely on small, soft-bodied caterpillars typically found in overgrown plants and open areas. Another potential urban stressor, he says, is the lack of holes and crevices in modern buildings, which house sparrows traditionally use for nesting.

Gowda says that one of the key lessons from the study is that conservation cannot rely solely on the species’ ability to adapt. “Additional pressures imposed by urban habitats need to be reduced. Increasing green spaces is one obvious step. Access to vegetation can improve the availability of nesting material and potentially food resources,” she says.

Waste management is another critical factor, adds Francila. In cities, poor disposal of food waste attracts predators such as crows, increasing nest predation risk. Reducing exposed food scraps and managing waste more effectively could help lower predator densities around nesting areas. Another key factor is disturbance levels which need to be minimised to improve breeding outcomes. The study findings suggest an urgent need to make urban environments cleaner and less stressful for the birds.

Read more: How urban birds respond to heat and green cover

Banner image: A female sparrow collects materials to build her nest. Image by Agnes Francila.

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Aditi Tandon Senior Production Editor

Topics

BirdsCities and TownsTamil Nadu

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