Red Slender Loris (Loris tardigradus) nocturnal tapetum lucidum: red-filter torch protocols?
Why do primatologists surveying endemic Red Slender Lorises in Kottawa arboretum use deep-red 650nm wavelength lights rather than white LED torches?
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3 Answers from travellers
The endemic Red Slender Loris (Loris tardigradus / Unahapuluwa) is an endangered nocturnal prosimian inhabiting wet-zone rainforest understories. They possess enormous forward-facing globular eyes equipped with an intensely reflective tapetum lucidum that reflects a glowing golden-orange eye-shine. Shining unfiltered white LED or halogen torches causes immediate pupillary spasms, photophobia, and temporary retinal blindness, leaving them unable to hunt insects or navigate thorny bamboo for hours. Field surveys mandate using headlamps fitted with deep-red photographic filters (wavelength 650nm+), which illuminate eye-shine without triggering retinal distress.
Walk softly along gravel paths; lorises freeze completely motionless upon hearing snapping twigs or loud voices, holding single postures for up to twenty minutes.
Urban canopy fragmentation around Galle and Matara forces lorises down onto live overhead electric cables, presenting severe electrocution risks.
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