Ammonite / Juvenile Mantled howler monkey (Alouatta palliata) climbing through canopy, showing use of prehensile tail, Santa Rosa National Park, Costa Rica.

Ammonite / Mantled howler monkey (Alouatta palliata) climbing through canopy, showing use of prehensile tail, Santa Rosa National Park, Costa Rica.

Doug Wechsler / Mantled howler monkey (Alouatta palliata) Buenaventura Ecological Reserve, Ecuador.

Phil Savoie / Mantled howler monkey (Alouatta palliata) in tree, La Selva, Costa Rica.

Phil Savoie / Mantled howler monkey (Alouatta palliata) feeding in tree, La Selva, Costa Rica.

Phil Savoie / Mantled howler monkey (Alouatta palliata) scratching nose, La Selva, Costa Rica.

Phil Savoie / Mantled howler monkey (Alouatta palliata), La Selva, Costa Rica.

Sean Crane / Mantled Howler Monkey (Alouatta palliata), Soberania National Park, Panama

Nick Hawkins / Mantled howler monkey (Alouatta palliata) calling, Costa Rica.

Nick Hawkins / Mantled howler monkey (Alouatta palliata) Costa Rica.

Nick Hawkins / Mantled howler monkey (Alouatta palliata) Costa Rica, March.

Nick Hawkins / Mantled howler (Alouatta palliata) riding on mothers back, Costa Rica.