The science behind eyeshine
Here in the northern hemisphere, the autumn days are getting shorter and shorter. It’s getting darker earlier in the day, and our eyes have to adjust to dim conditions.
Without the help of fire or electric lights, we humans are pretty bad at night vision. Unlike many other animals, our eyes lack a specialized reflective surface that aids sight at night and in low light environments (caves, under water, etc.). This surface, called a tapetum lucidum, located behind the retina, acts as a mirror to reflect light photons.
Humans lack the tapetum lucidum located in between the retina and choroid in the eyes of many nocturnal animals (Source).
Light enters the eye and hits photo receptors in the retina. Some light, however, will miss the photo receptors and pass past the retina. The tapetum lucidum reflects that light and gives it a second chance to hit the photo receptors and illuminate the scene.
Some of this light is reflected back out of the eye, which is why some animals’ eyes appear to glow in nighttime trail camera photos. All types of camera flash, even the low-glow infrared flash of the Snapshot Wisconsin cameras, can reflect off the tapetum lucidum and cause an animal’s eyes to light up. (This is not the same as the red-eye effect seen in photos of human eyes which is caused by light reflecting off the blood vessel-rich choroid behind the retina.)
There is variation in mineral content and structure of the tapetum lucidum, which causes eyeshine in different species – and even different breeds of dog – to look different. Eyeshine may appear white, blue, green, yellow, pink or red. It’s too bad nighttime trail cam photos are in black and white and we can’t see these color differences!
Animals having a tapetum lucidum (not extensive):
- deer
- carnivores: canids and felids
- grazing animals: sheep, goats, cattle, horses
- ferrets
- lemurs
- marsupials
- fruit bats
- ray-finned fishes and cartilaginous fishes including sharks
- owls and a few other nocturnal birds
- crocodilians including alligators (bright red eyeshine – spooky!)
Animals lacking a tapetum lucidum (not extensive):
- higher apes including humans
- kangaroos
- pigs
- squirrels*
*I’ve read that squirrels don’t have a well developed tapetum, but flying squirrel eyes certainly glow in our nighttime trail cam photos. Anyone who can shed some light on this mystery, please leave a note in the comments!
Sources:
- What causes the red eye effect? Yale Scientific Magazine.
- Candid Creatures: How Camera Traps Reveal the Mysteries of Nature. Johns Hopkins University Press.
- Why do animals’ eyes glow in the dark? NPR All Things Considered.
- Comparative morphology of the tapetum lucidum (among selected species). Veterinary Ophthalmology 7(1):11-22.
- Crystals of riboflavin making up the tapetum lucidum in the eye of a lemur. Letters to Nature.
- Ocular comparative anatomy of the family Rodentia. Veterinary Ophthalmology.
Vivek’s citizen science and camera trapping experiences
In this post, I’ll be talking a little bit about my experiences with citizen science and camera trapping projects prior to joining Snapshot Wisconsin.
Before I decided to become a wildlife conservation professional, I was involved with citizen science projects as a volunteer. I found pleasure in natural history, making observations and collecting data for scientists. This was my contribution to saving the world, I thought! As a volunteer, I have done large mammal surveys in India, from counting tiger prey species to collecting carnivore scat. I learned a lot from participating in these projects. More than anything else, I think they provided a welcome distraction from my day job as a software programmer *chuckle*.
Here’s a misty morning scene from Nagarhole National Park, while I waited for the survey start time of 6 am.
I was also involved with conservation groups in the Western Ghats landscape of India. One project I am proud of being associated with is the Bisle Frog Watch. Every year citizen scientists congregate at Bisle (a tiny village in the Western Ghats) to learn about amphibian ecology and identify them in the wild under the guidance of researchers. What is heartening is that over a period of 6 years, we have made a checklist of 36 species of amphibians!
A night time frog watching field visit in progress.
A regular feature of our frog watch: a winged gliding frog( Rhacophorus lateralis) perched on a rock.
Apart from mammals and amphibians, I also love bird watching and regularly submit my bird lists to eBird.
A whimbrel from the Western coast of India.
Some of these experiences with citizen science gave me the confidence that I too can do scientific research. And, that’s also how I decided to pursue a Master’s degree.
Talking about my camera trapping experiences, I worked on a trail camera survey in Ecuador for my Master’s capstone project. I worked with an Ecuador based non-profit called Ceiba Foundation for Tropical Conservation. We set up a total of 16 camera traps on several private properties and nature reserves in the Manabi province of coastal Ecuador.
Whereas the most common species in Snapshot Wisconsin is the white-tailed deer, in my project in Ecuador it was the agouti. (Although white-tailed deer have been recorded in the study site in Ecuador, they are uncommon in those parts of the world.) Whereas in Snapshot Wisconsin we see bobcats, in Ecuador we frequently recorded wild cats like ocelot, margay and jaguarundi.
In fact, I am even leaving an identification challenge for some pictures from Ecuador. Feel free to leave your guesses( along with the picture number) in the comments below. I shall post the answers soon-ish!
Picture #1
Picture #2
Picture #3
Picture #4
All in all, it is exciting to be working on the Snapshot Wisconsin project – with the many citizen scientists who host camera traps across Wisconsin and many others from around the world classifying pictures – knowing we have something in common.
Picture credits: Frog watch pictures – Deepika Prasad; Camera trap pictures from Ecuador – Ceiba Foundation for Tropical Conservation.
September #SuperSnap
This month’s #SuperSnap comes to us from CraftyWench. This turkey was captured flapping its wings while perched in front of an educator camera in Sheboygan County.
Check out all the nominations by searching “#SuperSnap” in Talk. Hashtag your favorite photos for a chance to be featured in the next #SuperSnap blog post.
Snapshot Wisconsin 