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.
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):
- carnivores: canids and felids
- grazing animals: sheep, goats, cattle, horses
- 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
*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!
- 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.
Our July #SuperSnap was all about fishers, and we’re just going to keep on rolling on the fisher train! This science update was inspired by recent comments on a photo of a fisher in central Wisconsin. The location of the photo might cause confusion if you base where fishers *should* be on the range map we have posted. The map shows fisher range extending to only the very northern part of the state:
Whereas we’ve seen fishers on Snapshot Wisconsin cameras in counties pretty far south:
In the case of a species like fisher, which was reintroduced to Wisconsin in the 1950s and expanded its range quickly, static distribution maps go out of date quickly. This brings up a larger point about range maps being inaccurate because they are based on old, incomplete or faulty data. We provide range maps to give volunteers an indication of where they are more likely to find a certain species, but these maps are by no means perfect. The fact that we do not have very good statewide data on the distribution of most species is indeed a major reason for starting a project like Snapshot Wisconsin!
Note that the above map shows counties where we’ve seen Snapshot Wisconsin photos correctly classified as fisher. Many of the gray counties do not have any Snapshot Wisconsin cameras and so we do not have any photos there yet. This is not to say there are no fishers in the gray counties!
This month’s #SuperSnap selection goes to this agile fisher nominated by @Snowdigger:
Fishers (Martes pennanti) are medium sized mustelids with slinky-like bodies and dark fur. Despite the name, fishers seldom eat fish. Instead, their diets consist of small mammals, and are one of a handful of animals capable of preying on porcupines. Fishers were reintroduced to Wisconsin in the 1950s, and have done well in the state since then – so well, in fact, that Wisconsin fishers have been re-located for reintroduction efforts in other states.
#SuperSnap is a monthly blog feature and a way for us to share some of the best Snapshot Wisconsin photos! Hashtag your favorite photos for a chance to be featured in the next #SuperSnap blog post, and check out all the nominations by searching “#SuperSnap” in Talk.
The following post is by a guest blogger, Joe Dittrich, research scientist at the Wisconsin Department of Natural Resources. Joe was involved in the new elk reintroduction in the Flambeau River State Forest (Sawyer County) and shares the experience here. Thanks Joe!
We’re happy to announce that enrollment is now open in six new counties, bringing our county total to 18. Any individual or organization in these counties with access to 10 acres of land is encouraged to apply to host a trail camera. We are also continuing to accept applications from educators and tribal members/affiliates across the state. Check out our project web page and monthly newsletter for complete updates!
Happy Spring! the Snapshot Wisconsin team in spending the month of May bopping around the upper Midwest for trainings, fieldwork and conferences, oh my! We’ve been checking in on Zooniverse from the road, but we apologize if we’ve been less responsive than usual this season. Here are some highlights:
New elk cameras!
A new cohort of elk will be released into the Flambeau River State Forest (FRSF) in Sawyer County this summer (south of the existing Clam Lake herd). The Snapshot Team traveled to FRSF to train volunteers who will be hosting cameras in this new area. We also got to tromp through the woods ourselves to put up some of the cameras, and came across lots of animal sign, wildflowers and other indications that spring has sprung.
Citizen Science Association conference
We learned a lot about the field of citizen science at the Citizen Science Association conference in St. Paul, Minnesota last week. At our tabling session we met all kinds of wonderful people managing citizen science projects, including other trail camera projects. It was wonderful to hear about all the fantastic work going on in citizen science, and we came home with a list of ideas on how to improve our own project. Team member Christine Anhalt-Depies gave a great talk about what motivates our trail camera hosts to participate in Snapshot Wisconsin.
New counties, new trainings!
This month, we’re providing trainings for our trail camera hosts in St. Croix, Oneida and Marinette counties. Stay tuned for 6 new counties opening for enrollment in the next couple weeks!
This Friday, May 19, Christine, Christina and Susan will represent Snapshot Wisconsin at a Night in the Cloud in St. Paul, Minnesota. For those of you in the Twin Cities area, come down and learn about 100+ hands-on projects & see a screening of “The Crowd and the Cloud.” We’d love to see you!
Thanks to a dedicated effort by our volunteers, Wisconsin DNR staff and University of Wisconsin students, we were able to classify all of the elk photos from 2016!
This Science Update features data from the Clam Lake elk area only, due to a lack of elk photos from the Black River Falls area. From GPS collar information, we know that many of the Black River Falls elk prefer to hang out outside of our camera area (perhaps they are bashful?). When we have more Snapshot Wisconsin cameras in the counties surrounding Black River Falls, we hope to have enough data for a Science Update on those elk as well.
There were 120 cameras active in the Clam Lake area in 2016, capturing 3,996 triggers containing elk. After grouping consecutive triggers showing the same elk, we ended up with 305 unique elk events.
We graphed daily activity patterns of antlerless elk and bulls from the 305 unique elk events. Overall, elk were most active between 6 and 9 AM and 5 and 6 PM. Antlerless elk were most active around dawn and dusk, while bull activity peaked later in the morning and evening.
We also graphed monthly elk activity throughout 2016. Because not all of our cameras were active during the entire year, we corrected photo hit rate based on the percentage of cameras active each week. The image below shows this corrected photo count for antlerless elk and bull elk throughout 2016.
The marked spike in bull activity at weeks 36 through 40 indicates the annual rut period. That period corresponds to a sharp drop off in activity level for antlerless elk; cows tend to stay put during that period while bulls move around more. (Curious about why this might be? Click here for more information on elk life history and mating behavior.) The trail cameras give us the ability to pinpoint the time frame of the rut period more precisely than we were previously able.