When a zookeeper cannot access an exhibit because it is blocked, put the zookeeper in the exhibit. He or she will place the food. Then, take him or her out again and put them back on the path.
Alternatively, adopt a herbivore such as a tom gazelle or a sheep family animal into a carnivore's cage. Although red angry faces will rise up from the carnivore's head, it will chase after the herbivore. Wait and the herbivore will disappear.