If you are after a weather proof body (as compared to a waterproof body) you really cannot fault the "1" series bodies from Canon. They are not only weather proof but they are equally bullet proof. I have also heard the 7DII body in the canon range is also weather proof.

Most "L" lenses when coupled to the "1" series bodies are also equally weatherproof (especially in the large telephoto range of lenses).

Bear in mind you will pay for the privilege of using a "1" series body but if you need a body that can be used in almost any conditions then they are worth every cent. if you are in particular need of a birding body then I would look at the 1DIV which can be picked up used at quite an attractive price now. This can be coupled with the 150-600 sigma sports range and you have an excellent weatherproof birding set up.