Other animals like cows get lots of calcium by eating grass
They then pass on some of that calcium by milk
The rest they put primarily in their own bones and teeth and secondarily in other parts of their body
So unless someone eats cow bones then milk is a much better source of calcium then meat
In the case of female birds they put calcium primarily in the skeleton and the shells of eggs
Again their meat is not a good source of Calcium
Other animals eat for many hours more per day than humans and can digest calcium containing foods that humans have trouble digesting