Christopher the lion is no longer on exhibit, due to health issues. Here is the announcement from the zoo's Facebook:
"As we shared in January, Christopher the lion is being closely monitored and treated for several irreversible, age-related issues. Recently, his health has begun to decline further and due to this he will no longer be seen on exhibit. At age 21, Christopher is among the oldest lions within the North American captive population in facilities accredited by the Association of Zoos and Aquariums. The median life expectancy for lions is 16.8 years. The veterinary and animal care staff take extraordinary care of our geriatric animals, as they do with all of the animals in our collection, to ensure that they enjoy a comfortable life as they continue to age, which is often far longer than the median life expectancy. Great care is being taken to ensure that Christopher is comfortable and has access to plenty of enrichment and stimulation."