Leviticus 11:3–8 and Deuteronomy 14:3
Of all listed kosher land and air animals, as a rule rather than the exception, none consume other animals. In regards to birds in particular,
All predatory birds are not kosher. The kosher ones do not eat other animals. Is it specified, that kosher birds abstain from meat, no, but is the distinction between herbivore and carnivore birds clear, yes. Lastly, regarding unclean meat,
Unclean meat goes to the dogs, which are not kosher. I realize the correlation isn't exact (the meat could theoretically go to a chicken), but it is written for the meat to go to a non-kosher creature, a dog.
Edit: the torn meat exo 22:31 refers to would be of an otherwise kosher animal, not of a non-kosher creature (which would be understood without exo 22:31 specifying it). What is left unclear by this passage is what if the torn meat was not kosher to begin with, could the dog still eat it? Or is it subtly implied that while an improperly torn animal can be fed to a dog, a non kosher animal shouldn't be fed even to a dog...
These factors led me to consider that man is responsible over what his animals eat. Therefore, when feeding a chicken only pork, by the will of man, it seems that the qualities which make the chicken kosher are intentionally reduced/altered.
I would therefore say that a chicken on a pork only diet cannot be kosher. Potentially, any non kosher food intentionally fed to an otherwise kosher creature would disqualify it. Would you eat such a chicken?