I suppose a question that has to be asked is "Do you have to photograph everything" and at 'all times of the year'? Is the photography of it all that important to you, or....can you find just as much enjoyment by skipping the camera and lens, and merely bird with your binoculars?
Frankly under some of those conditions, are you really going to get that 'perfect shot' ...7D or 5diii or whatever?
I know around my 'local patch' (I love that British term)....I am pretty familiar with my birds and find that at certain times of the year, it is way more enjoyable just to bird with bino's....take a walk and not have to worry about the light, the image etc. .... Just my thoughts, jim