Learn. Contribute. Explore.
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If you want to learn more about a particular species, birdsoftheworld.org is a brilliant resource.
To discover which birds are present in your region, check out ebird.org - you can also contribute by uploading your own sightings. They have an extensive collection of photos, recordings of calls, distribution and migration maps and much more.
Bird Count India is another fantastic resource with articles on getting started with birding, species ID, and monitoring. They also list up-to-date information about events and workshops.
This article by FatBirder has some great suggestions for where to go birding in and around Delhi.
Want to buy binoculars? This article by Jungle Buddies is a great place to start.
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Some recommended books:
A Pictorial Field Guide to the Birds of India by Bikram Grewal, Sumit Sen, Sarwandeep Singh, Nikhil Devasar and Garima Bhatia is a beautiful book with clear pictures and lots of information; however as it covers the entire subcontinent it can be quite hard to find a bird if you don’t know its name. It’s also very big and heavy so more suitable for home use than taking out into the field!
The Birds of the Delhi Area by Sudhir Vyas narrows down the selection of birds from the India guides, however note that it is not a field guide and so not every entry has a photograph.
Birds About Delhi: A Field Guide by Nikhil Devasar and Rajneesh Suvarna is the only Delhi-specific true field guide I can find, however it appears to be out of print at the time of writing. You may be able to find it second hand!
Please consider buying books from local, independent book shops before giving your money to big online companies (though admittedly this can be hard with niche nature books!)