Young Zebra Visitor

This morning Bonnie (our Husky-cross dog) was staring intently across to the end of the road. This meant that something intensely interesting was there - so I went out quietly to have a look.
There it was - a young zebra lying at the corner of the road.
How does Bonnie know not to bark at it?
She seems to have learnt that Zebras here are part of the family. Her first encounter was very exciting when four zebras were grazing just outside the fence of our front garden.
Both she and Bess (our bull-terrier cross) were barking frantically when I went to see what was up - and managed to calm them down and get them to stop barking.
 The zebras seemed to be unperturbed, totally 'in charge' of the situation, and carried on with their meal! They moved off, but a short while later came back and just stood looking at the dogs - who this time did not move or bark.
It seemed as if there was some sort of communication going on between the species.

Hopefully both dogs will learn that the wild animals around us are part of the environment and not to be barked at.