Sounds, Sights & Smells in tropical Rianforests

Mike Boston

Mike is an honor’s biology graduate of the University of Portsmouth and is the owner / operator of Osa Aventura, the premier guiding outfitter for Corcovado National Park, and has led groups into the Park for the past eighteen years.  Contact him directly at mike@osaaventura.com.



When I’m guiding my senses are on high alert.  I’m a hunter stalking my prey in much the same way as a puma, or any other predator.  Unlike a puma, however, I don’t seek to kill my prey.  I just want to see it.

Just hearing or smelling my prey won’t cut it for me, I must see it – I am a primate, after all, and vision is everything.  But, sight is limited in rainforests to a few tens of meters.  Sound and smell carry much further and are, most often, the frontline senses in finding my prey.

Tropical rainforests hold a kaleidoscope of smells that are often hard to interpret.  With odorous animals, such as the peccaries, smell is often frontline in their sighting.  Tamanduas have a vapid, musty odour that often alerts me to their whereabouts.

Sounds are easier to interpret.  Sounds come in two categories: vocalizations and non-vocalizations.  Vocalizations not only give me a direction and distance, but an identity too – with experience!    When I hear the panicked whaah, whaah, whaah…., I know it is the alarm call of a concerned spider monkey upon seeing one of its’ predators – I have seen several pumas from this auditory cue!  Birders are especially tuned into the vocalizations of their avian quarry.

Non-vocal sounds can be a little more challenging to interpret.  The crashing sound of leaves in the forest canopy can, for example, indicate the presence of monkeys.  One category of non-vocal sounds is the noise of objects hitting the forest floor that have fallen from the canopy – branches, leaves, fruit, water droplets, animal urine, faeces and miscellaneous bits and pieces .  Interpreting these sounds is one of the most lucrative ways to find my animal prey.



However, there are two canopy dwelling animals whose presence I’m never alerted to by sound or smell, the sloths.  Two and three-toed sloths are among the most abundant mammals in Neotropical rainforests.  Estimates from Barro Colorado Island, the Smithsonian’s tropical laboratory in Panama, put three-toed sloth density at 70 per square kilometer, making it the most abundant mammal there.  Yet, without auditory or olfactory cues, finding sloths is notoriously difficult.

Spider monkey

Spider monkey

It has been a puzzle to naturalists why sloths descend from the forest canopy to defecate and urinate on the forest floor.  And why they do so infrequently, just once a week.  Many fanciful explanations have been put forward to explain this odd behaviour.  One theory proposed is that sloths are recycling nutrients back into the trees they feed upon.  Another theory posits that the sloth is facilitating the life cycle of the moths and beetles that live in its fur whose larval stages feed the sloths faeces.  For this idea to hold true, the moths and beetles must bring some significant benefit to the sloths.  But, it is not at all clear that they do!

A more likely explanation for this habit is that sloths do not want to draw the attention of predators to their location in the canopy by defecating noisily from on high.  Unlike monkeys, sloths do not have the agility to flee from predators once seen by them.  They are sitting ducks.  By descending to the ground to defecate silently the sloths risks being seen by a predator, but sight is more limited in range in rainforests than sound.  The noise of faeces crashing onto the leaf litter of the forest floor is more likely to heard by a predator from further away than its visible range. To offset the risk of this pooping habit, sloths defecate very infrequently compared to other mammals.


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