what do you take for calcium then? And protein?
I have been vegan for such a long time (19 years) that I find it difficult to answer this question directly. I guess we just eat 'well'. I eat tons of calcium-rich vegetables and consume a lot of legumes. I see a trend with people who become vegans where the whole 'three meals a day' thing is abandoned. We graze. We snack on nuts and fruit, our meals are usually beautiful, large, (vegans also tend to become extraordinary cooks) and gloriously nutritious. Leftovers are common (no animal products leaves less problems in re: rot) as we tend to cook in batches (much the same way we make our bird food).
It is just a completely different way of eating and viewing the process of consuming food. Luckily, there is a lot of 'fake' animal-type-things these days which makes the transition easier for folks (though this stuff will be abandoned after any significant time being cruelty-free, simply because of how expensive it is).
The real problem, in my experience, comes with leather and other things not diet-related. People seem to 'hate fur' but fail to see the hypocrisy in their leather shoes. Once that ethical conundrum is processed, you are well on your way to being a friend.
Edit: In re: Diet: Getting a good Mediterranean, Middle Eastern, Indian, and/or any random vegetarian East Asian cookbook usually sets one up for an astonishingly good place to begin eating healthy without animal products. While substitutions are usually necessary if the book isn't declared 'vegan' (a Korean vegetarian cookbook is a favorite of mine, and ground flax substitutes eggs, rice milk substitutes milk, etc., and everything is lovely) such books are a good place to discover the possibility of astonishing dishes that do not require an animal to make them delicious, beneficial, and fulfilling.
It's worth noting that once vegan: Your birds can literally eat everything you eat and you can eat everything your bird eats. This is a huge step in creating a fun, family dynamic if living with free birds (it has proved monumental in doing what I am doing over here).