The 15 threatened animals were shot dead for their horns last month in the Mozambican part of Great Limpopo Transfrontier Park, which also covers South Africa and Zimbabwe.
They were thought to be the last of an estimated 300 that roamed through the special conservation area when it was established as "the world's greatest animal kingdom" in a treaty signed by the three countries' then presidents in 2002.
"Rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add 'within the limits of the law' because law is often but the tyrant's will, and always so when it violates the rights of the individual." Thomas Jefferson