Michael Watkins, 22, pleaded guilty to felony attempted grand theft and cruelty to animals, according to the Ada County Prosecutor's Office.
He had originally been charged with felony burglary and grand theft and was scheduled to go to trial in May.
Prosecutors say Watkins had hoped to steal the animal before he was bitten and clubbed it to death with a tree branch.
A security guard spotted the Watkins, who ran, and the animal died a short time after it was found by zoo officials.
The maximum sentence for the attempted grand theft charge is 7.5 years in prison.
Watkins is scheduled to be sentenced on May 16.