We had one female that would religiously go off feed for 10 months out of the year and would never eat an appropriate sized meal.
Her feeding schedule would go something like this:
Eat 1 undersized rat.
Fast for 3 weeks.
Kill undersized rat but not eat it.
Fast for 4 weeks.
Eat 1 undersized rat.
Fast for 2 weeks.
Kill undersized rat but not eat it.
Fast for 10 months.
Repeat next year.