How to mogrify recursive folders compacting the files

I need to excute in ubuntu something like this:

find ./ -name '*.jpg' -execdir "mogrify -quality 50 *.jpg" {} \;

To compact all the *.jpg to 50% of your quality but this need to be recursive, because i have 1350 files in a long tree of folders...

And this return ever something like:

mogrify: unable to open image `Banner-Caixa.jpg': permission denied @ error/blob.c/OpenBlob/2712.