"Sunday! @TheLosAngelesZoo Thank You Lt. Beccera for looking after us! @selanagomez @justinbieber #lazoo #mydayinla #sunday," Instagram user Dave Osokow captioned a photo.
Gomez, 21, and Bieber, 20, first started dating in their teens.
A source recently told E! News that Gomez has been reluctant to give up Bieber up for good.
"She still loves him," the source said. "It is hard for her to get over him, because they have so much history."