"He did have to jump over a fence that has a no trespassing sign and had to climb over the barbed wire that was on top of it to actually get into the zoo itself," Lt. Jennifer Horsford, Fresno Police Department.
The trespasser has been identified as 38-year-old Julio Mendez. He was spotted by zoo security walking through the African Adventure area.
Mendez ran away and attempted to climb an 18-foot high mesh to get away from security.
That's when one of the lions in the exhibit stood up on her back feet and bit Mendez on his left big toe.
"They are incredibly strong, and they are dangerous. They have both of course claws and massive canine teeth, and so this person got very lucky about the injuries they received," said Scott Barton, Chaffee Zoo Director.
Barton said it is not known which one of two female lions from the exhibit bit the Mendez.
Each lion was checked out by a veterinarian because police say Mendez was under the influence.
Barton said his security staff is now reviewing footage from 50 different cameras and will take a closer look at security procedures currently in place.
But he wants the public to know they are safe when they visit the Chaffee Zoo.
"We have a very professional and well-trained team and this was brought about by human behavior, not by animal behavior," said Barton.
Police found drug paraphernalia on Mendez and say he will be cited for trespassing.