Another thought that struck me was why they would want to escape? I think that maybe they spotted something outside the zoo fence, Fox, Badger or dear and decided to give chase, i can understand them getting out of the enclosure but then to escape the zoo boundary at roughly the same time, something must have stirred them on. All very sad as I keep saying. The only other explanation is some one didn't close the gate correctly and it swung open? then they panicked realizing they weren't in their own space.