I always believed that nests are built of grass and straw which a bird finds in fields and gardens. But I had to change my belief when I saw a crow's (most probably crow...but not 100% sure) nest which fell out of a coconut tree in a semi-residential area of bangalore. It weighed about 3 kgs or more and was built of mostly short metal wires with only a bit of straw & cotton in the centre to make a soft cushion for the birds and their young ones! The wires were so interlocked, it was difficult to take the nest apart! It was an amazing feat of weaving, done only with a beak and two legs maybe! If I had had a camera then, I could have taken a photo maybe.