As we retreated to our dwellings in the "anthropause" of spring 2020, were the wildlife sightings in previously crowded spaces a reclamation of habitat, or a mere increase in detection? We leverage an increase in balcony birdwatching, a million eBird entries, and difference-in-difference techniques to test if urban avian species richness rose during India's COVID-19 lockdown. Controlling for effort, birdwatchers in the 20 most populous cities observed a 16% increase in the number of species during lockdown. While human activity stopped overnight, and noise and visual pollution decreased soon after, increased species diversity was observed 1-2 weeks later; evidence that gradual population recovery, not better detection, underlay our results. We find at-risk, and rare, species among those reclaiming cities, implying that reducing human disturbance in urban areas can protect threatened species. Increased species diversity likely derives from a reduction in noise and air pollution associated with the lockdown, implying that urban planners should consider conservation co-benefits of urban policies when designing sustainable cities.