(This probably makes more sense if you're British.)
Doing his rounds one day and when he got to the bird enclosure he noticed a load of the birds had died. Unsure as to what he should do with the bodies he tossed them into the big cat exhibit.
The next day he was cleaning out the primates and noticed the lifeless figure of an ape laying on the floor... not wanting to perform a proper burial and besides- he wasn't earning much more than minimum wage anyway so he tossed it into the big cat enclosure.
On his third day the zookeeper came across his colleague who kept bees, it seems they'd got sick and a lot of the hive had perished. Not to worry, the zookeeper scooped them onto a shovel and tossed them into the big cat exhibit. It's the circle of life he thought to himself.
The next day there was a lot of excitement in the zoo. A new lioness had arrived. The lioness stalked out of the trailer...sniffed at the unfamiliar lion next to her...
"So, what's the food like in this place then?" She asked awkwardly.
"It's actually not that bad" replied the lion. "Over the past few days we've had Finch, chimps and mushy bees"
Badum tssss! ¯_(ツ)_/¯
Yeah, for any non brits that read all that: Fish, chips and mushy peas is a classic English dish. So...yeah...that's the joke.
Dad Jokes are great and all, but I'm more into Sun Jokes. They're a little st-upiter and talk about Uranus a lot, but they're equally funny.
I went to practice my joke routine at a cemetery recently. The audience was really lifeless. Except for this one guy, he had a really deadpan laugh though.