A few weeks ago, two cats came to the patio door. One is a ginger cat, quite
big and well fed looking, the other - who has the same kind of collar -
looked kind of skinny. They sat there staring in so I felt bad for them and
set out a dish of food. They gobbled it up in seconds and now come by every
day for a meal and then lounge on the deck. Anyway, the skinny one has a
nice coat of fur on its head and almost half way down his body... like a
sweater... the hind part is almost all free of fur. There is the soft under
fur but not much. What could cause this? Since the two cats have the same
collar and only come out during the day, we assume they do have a home. They
don't look like strays or feral. My own two cats don't mind them much but
will stare... no hissing. I would like to try and attach a note to one of
them saying I am feeding them in case their owners are worried they are not
eating as much and to see that the deal is with the fur but they are a bit
skittish when I go to approach them (other than the food bowl I bought
them).

any suggestions are appreciated.