Location: Any night time wilderness setting while the party is camping.
Scenario: While the party is camping, their horses become skittish sometime around midnight. Nothing appears out of the ordinary and the party is unable to detect anything causing their nervousness. (You can set a perception check with moderate difficulty for party members to have a chance at hearing the faint flapping of wings.) Then all is quiet once more. Approximately one hour later, the sentries again notice the horses becoming restless.
Suddenly, out of the dark sky, the PC’s see a pack of griffons swooping in to attack the party’s horses. The griffons ignore the PCs, more intent on the opportunity to feast on horse flesh. If the PCs abandon their horses, the griffons are more than happy to eat them and leave soon afterward. They ignore the party as though they aren’t even there.
However, if the PCs decide they would rather ride than walk, and that keeping their horses alive would best suit this end, they must fight the griffons. Attacking the creatures however,only serves to call their attention to the PCs. The griffons not directly attacking the horses fly at the party members and attack ferociously.