A new expedition set out and found an excellent, well defensible location near a deep river gorge. Things were pretty quiet as the initial tunnels were being dug. Outside the soon-to-be-fortress the dwarves set up a kitchen and still, cooking food and brewing beer. Stockpiles of consumables and materiel were set up, ready to be moved into new storage rooms underground.
Then, without warning, a swarm of rhesus monkeys attacked the camp!
The monkeys harassed the dwarves, going so far as to bite one of the miners. Several monkeys made off with freshly cooked food. It was utter chaos in the camp!
Only a quick-thinking animal trainer saved the day. Rushing to build a kennel, he trained several wardogs which then slaughtered the simian pests. The result: plenty of fresh monkey-meat to replace the stolen food, plus extra leather (for armor) and fat (to render into tallow for soap). Unfortunately, the bitten miner succumbed to an infection and died.
UPDATE: Those monkeys returned again. This time they stole a masterwork silver dagger created by a stonecrafter dwarf. The dwarf was so upset by the theft that he threw a tantrum and killed a nearby donkey. This seemed to calm him down for a few minutes, but then he suddenly flew into a berzerk rage! After killing numerous puppies and kittens and felling three of his fellow dwarves, he was finally taken down.