To enhance your hunting and combat capabilities in Assassin's Creed Black Flag Resynced, acquiring red howler monkey pelts is essential. These pelts are used to craft the "Dart Pouch II" upgrade, increasing your dart capacity to 11, and can also be traded for special vanity items like the Pallas Athena figurehead.
The red howler monkey can only be found on Isla Providencia, specifically on the southern portion of the island at coordinates (480, 16). This island becomes accessible during the "Marooned" main quest, so players who have not progressed this far in the story will not find it on their map.
Upon reaching the island, head towards the western viewpoint. From there, follow the path eastward and take the first right turn. The red howler monkeys are situated in the trees behind a fallen rectangular pillar, near a small pond. A second monkey can be found slightly further ahead, beyond a large stone wall. Utilizing Eagle Vision will make them easier to spot.
While a pistol can be used, shooting one monkey may frighten the other. It is recommended to use sleep darts for a more effective approach. Looting the monkey's body will yield one bone and one red howler monkey skin.
To maximize your rewards, equip the Exotic Sea Shells trinket for double drops. Alternatively, you can advance time or travel to a different region to reset the monkey spawns and collect more pelts.