Thursday, 21 February 2013

The Back Patch Mystery


Sloths have many weird and mysterious behaviors that we are constantly trying to understand... Why are they so slow? Why do they come down to the ground to defecate? How long do they sleep for? These are all the common questions. The fact that male three-fingered sloths have evolved bright orange patches on their backs seems to have been completely overlooked! Considering a sloths survival strategy is camouflage, this sticks out like a neon flashing light!



Why have these bright back patches evolved? What is the benefit? Why don't females have them? Why does patch size and color differ so much between individuals? This begs so many questions that we are hoping to answer here at the Sloth Sanctuary.

We have learnt over time that male three-fingered sloths develop these patches as they reach sexual maturity at approximately 1 - 2 years old.  They are always yellow or orange in color and divided by a central black stripe with additional black markings in a pattern unique to each individual.The type of hair within the patch is completely different in texture to the rest of the sloths hair and doesn't grow any algae. Interestingly, the patch appears to be covered in an unknown oily secretion and if you touch it, the yellow/orange pigment rubs off! 



The result of rubbing the patch with a cloth:


The (infuriating) video below was posted by a man who studies sloths in Panama. They claim that if a female sloth smells the oily back patch of a male, she will produce a loud vocalization. Unfortunately this is nothing but a fairy-tale, yet another example of terrible sloth science!  



We have studied female vocalizations here at the Sloth Sanctuary and we know that they produce these screams for 10 days every month while they are in oestrus - regardless of any males present! The vocalizations attract male sloths into the area. It wouldn't make any sense for a female to scream if she was already with a mate! We did however test this theory out just to be sure - we rubbed the back patch of a wild male and held it under the noses of both a female who was in oestrus and a female who wasn't. Surprise surprise neither vocalized upon smelling the patch! Unfortunately this video is completely faked and probably explains the strange camera angle...!

 So the mystery continues. I am determined to find the reason for these big bright back patches and so have recently begun a study looking at this. Do bigger stronger males have bigger brighter patches? Does the patch size simply relate to body size? Do the patches get darker with age due to the continuous secretion of oily pigment? 


To test this, I am on a mission to find as many different male sloths as I can. Luckily as the females come into oestrus here at the Sanctuary we get an influx of testosterone fueled males from the surrounding forest. I catch them and take measurements of body size, weight, patch size, pattern and color intensity. 

We are building a male sloth back patch library!! 



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