Delhi Bird Atlas Explained: 471 Species, the Central Asian Flyway and Bird Diversity

What an atlas is: A bird atlas is a systematic record of the distribution and abundance of bird species across a defined area, usually built on a grid so that coverage is even and comparable over time. Unlike a simple checklist, it captures where and how commonly species occur, creating a scientific baseline against which future change can be measured.

The grid-based, equal-effort method: For Delhi, the city was divided into large grids of 6.6 km × 6.6 km, further split into smaller sub-cells. From these, 145 sub-cells were randomly selected for sampling — randomisation reduces bias and ensures different habitats are represented. Surveyors walked fixed routes and submitted four 15-minute "equal-effort" checklists per sub-cell, uploaded to eBird. This standardised design is what allows the atlas to claim it reflects the "true distribution and abundance" of species rather than just where birders happen to go.

Part of a wider movement: The Delhi exercise follows other Indian city/state atlases built the same way — such as the Kerala Bird Atlas (among Asia's largest) and the Mysuru City Bird Atlas — all powered by Bird Count India and the global eBird platform.

An ecological intersection: Delhi's diversity comes from sitting where several landscapes meet. The Delhi Ridge — the northern tail of the Aravalli Range — brings a dry, rocky forest landscape into the city; the Yamuna and Sahibi (Najafgarh) floodplains and wetlands provide refuge for waterbirds and migrants; and proximity to the western Himalayas aids seasonal movement of species.

Position on a migratory route: Crucially, Delhi lies close to the heart of the Central Asian Flyway, making it a seasonal haven for birds travelling from as far as Central Asia and the Arctic. The atlas stresses that this richness survives despite intense urban pressure, underlining the value of protecting the city's "green and blue spaces" — forests, wetlands, riverine systems, grasslands and floodplains.

Flyways explained: A flyway is the broad geographical route that migratory birds follow between their breeding grounds and wintering grounds each year. The Convention on Migratory Species (CMS) recognises nine major flyways worldwide; India is covered mainly by the Central Asian Flyway and the East Asian-Australasian Flyway.

The Central Asian Flyway (CAF): The CAF spans a vast area of Eurasia between the Arctic and the Indian Ocean, comprising migration routes from breeding grounds in Siberia (Russia) down to wintering grounds in South and West Asia and the Maldives. It covers about 30 countries, including India. Birds using it cross many international borders, which is why coordinated, cross-country conservation is essential.

The IUCN Red List categories: Species are classified by the International Union for Conservation of Nature (IUCN) into categories of rising risk — Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, and then Extinct in the Wild and Extinct. The atlas's "Endangered," "Vulnerable" and "Near Threatened" labels follow this scale. (IUCN statuses are revised periodically, so some species' categories may change over time.)

Endemic species: An endemic species is one found exclusively in a particular geographic region. The Delhi atlas reported 18 such species, alongside threatened birds like the Egyptian Vulture and Black-bellied Tern, signalling that the city hosts birds of real conservation importance, not just common urban species.

Citizen science: This is scientific data-collection carried out with the help of non-professional volunteers — here, birdwatchers, students and forest staff. Platforms like eBird (run by the Cornell Lab of Ornithology) and the collective Bird Count India let thousands of observers feed standardised observations into a common database.

Why the rigour matters: Casual bird lists tend to over-represent popular hotspots. By using randomly placed grids and equal-effort checklists, the Delhi atlas reduces this sampling bias, so its picture of which birds are common, rare or declining is far more reliable — and far more useful for urban planners and conservation managers making decisions about land use.

Birds as bioindicators: Birds are sensitive indicators of environmental health — shifts in their numbers, ranges and habitat use reveal stress on ecosystems, pollution and the effects of climate change. A long-term atlas, repeated every few years, turns these signals into measurable trends.

Urban biodiversity and green-blue infrastructure: The atlas shows that a megacity can still harbour exceptional biodiversity if its forests, wetlands and floodplains are protected. It identifies the Yamuna floodplains in particular as a key ecosystem for conservation and restoration, and makes a data-backed case for integrating biodiversity into city planning.

International commitments: India is a party to the CMS (Bonn Convention, 1979), the Ramsar Convention on wetlands, the Convention on Biological Diversity (CBD) and CITES. India hosted CMS COP13 at Gandhinagar in 2020 and launched the National Action Plan for Conservation of Migratory Birds along the Central Asian Flyway (2018-2023), aimed at reducing threats to migratory birds and their habitats. At CMS COP14 (2024), India led the adoption of an Initiative for the Central Asian Flyway to coordinate conservation across the 30 range countries.

Domestic laws and habitats: Protection is anchored in the Wildlife (Protection) Act, 1972 and the Wetlands (Conservation and Management) Rules, 2017. Key habitats around Delhi include the Okhla Bird Sanctuary (on the Yamuna, an Important Bird Area), the Najafgarh wetland, the Asola Bhatti Wildlife Sanctuary in the Ridge, and the Yamuna floodplains themselves.

The atlas's central message is that Delhi's bird wealth depends on protecting its green and blue spaces, so the priority is safeguarding and restoring the Yamuna floodplains, the Najafgarh wetland and the Aravalli Ridge against encroachment, pollution and unplanned construction. The survey should be sustained as a long-term monitoring tool, with repeat atlases every few years to detect population and habitat shifts early. Biodiversity data needs to be integrated into urban planning — including the Delhi master-planning process — so that infrastructure decisions account for ecological value. Finally, India should continue to strengthen implementation of the Central Asian Flyway action plan and wetland-protection rules, while expanding citizen-science participation to build public stewardship of urban nature.