Ever notice how deer placed by the player will not run when one of them is attacked, or even wander around?
Ever notice how deer next to other deer will sometimes only trigger some of them to run away?
This is because of the "Herd" mechanic. A group of deer (or any GAIA food units) needs to be made into a herd for them to flee when one of their herd is attacked.

To set a herd, select the "Objects" tab, then the "Herd Editor"

Select the deer (or other units) you wish to make into a herd (holding "Shift"+"Left Click" can help add/remove objects). After they are selected, press "Create Herd" to make them act together like a herd.
That's it! Just rinse and repeat for every other herd that you wish to create
Source: https://ageofempiresonline.fandom.com/wiki/Scenario_Editor/Deer
Ever notice how deer next to other deer will sometimes only trigger some of them to run away?
This is because of the "Herd" mechanic. A group of deer (or any GAIA food units) needs to be made into a herd for them to flee when one of their herd is attacked.

To set a herd, select the "Objects" tab, then the "Herd Editor"

Select the deer (or other units) you wish to make into a herd (holding "Shift"+"Left Click" can help add/remove objects). After they are selected, press "Create Herd" to make them act together like a herd.
That's it! Just rinse and repeat for every other herd that you wish to create
Source: https://ageofempiresonline.fandom.com/wiki/Scenario_Editor/Deer