Chickens are already recognized as a food source to coyotes. Your fenced in area and diligence as a responsible chicken owner may have lessened the opportunity for them to stop in and have a snack.I live in a rural area with lots of coyotes. Because there are very few houses and NONE have chickens I have never had a problem. My birds only free range 2-3 hours a day in the main fenced yard around the house.
When the neighbors talked about getting chickens I told them the coyotes had never been a problem BUT if people start letting their birds run loose all day the coyotes would discover they are a food source and then all the chickens in the area would be at risk.
If free chicken dinners are offered wildlife will take up the tempting offer.