We went to the San Diego Zoo during a major heat wave, and sadly, most of the animals were not out on exhibit.
"Oh, the Lions are off today." "Oh, the tigers are off today too." Oh, and the Polar Bears, they're off today as well..."
You get the picture. Basically half of the zoo was closed off. I was pretty disappointed to miss out on seeing so many of the big animals, but we still had a fun day. And it was hot.