These screech owls have huge eyes well suited to hunting at night.
Whether because of the movies, television or personal experience, just about everyone is familiar with the ghostly green images portrayed by night vision equipment that helps humans see in the dark. This is relatively new technology for mankind, but many animals have solved the dilemma of how to see in the dark many eons ago.
For most animals, seeing in the dark is easy, a result of a combination of physical and chemical adaptations and it takes a little optical background to understand it. It starts with the retina.
The retina, or back of the eye, is covered with light sensing cells called cones and rods. The cones are in the center and are responsible for vision during bright conditions. They also detect color.
Rods circle outside the cones in the retina. During daytime, these cells are essentially inactive and are not very sensitive to color. They slowly become activated when light dims and the pupil dilates, and a protein, Rhodopsin (cones use Photopsin), is activated. If you go from bright to dark, your eyes may require up to 45 minutes to fully charge the rods with Rhodopsin although most of the process will occur within six minutes. However, if you catch a quick flash of bright light, the Rhodopsin blanches and the process starts again. Red light doesn’t deactivate Rhodopsin and thus red lights are often used when humans work in light sensitive areas.
Animals utilize a number of strategies to essentially boost either the number of rods or their function. For many nocturnal animals, the nuclei of the rods undergo a pattern shift shortly after birth that enhances night vision. Their rods are also stacked in such a way as to create a multiplier effect, increasing light sensitivity by up to eight times with the same number of rods.
Often, nocturnal animals have larger eyes. Larger eyes mean more rods and more rods means better night vision. For example, the tarsier, a tiny arboreal mammal, has eyes that are larger than its brain. It is reported to be able to see well enough to hunt in total darkness. Owls also have huge eyes. In fact, their eyes are so large that they cannot rotate in their sockets and so owls move their entire head to look at something.
Some animals have developed pupils that can open extra wide. This ensures that every rod is available for light detection.
Many animals also have a tapedum lucidum. This is a reflective layer at the back of the eye that reflects light back through the retina increasing the light available to see by. This is also the layer that is responsible for eyeshine, that eerie red or green glow that we see when an animal is caught in the headlights.
Like so often in life, excellent night vision comes with a cost. For many nocturnal animals, excellent night vision costs them color vision as more rods mean fewer cones. The tapedum lucidum also decreases sharpness of the image the eye sees.
The ability to see at night—to hunt, to forage or to escape predation, opened up one of the great habitat partitions in the natural world. With night and darkness ruling half our lives, it was one smart move.
Help Idaho Wildlife
When we traveled across the state in October, most of the vehicles we saw using the wildlife management areas did not have wildlife plates.
C'mon folks, let's help Idaho's wildlife by proudly buying and displaying a wildlife license plate on each of our vehicles!
See below for information on Idaho plates. Most states have wildlife plates so if you live outside Idaho, check with your state's wildlife department or vehicle licensing division for availability of state wildlife plates where you live.
Wildlife License Plates
Idaho Wildlife license plates provide essential funding that benefits the great diversity of native plants and wildlife that are not hunted, fished or trapped—over 10,000 species or 98% of Idaho’s species diversity. Game species that share the same habitats (such as elk, deer, antelope, sage-grouse, salmon, trout) also benefit from these specialty plates.
No state tax dollars are provided for wildlife diversity, conservation education and recreation programs. Neither are any revenues from the sale of hunting or fishing licenses spent on nongame species. Instead, these species depend on direct donations, federal grants, fundraising initiatives—and the Idaho Wildlife license plates.
Both my vehicles have Bluebird Plates. I prefer the bluebird because the nongame program gets 70 percent of the money from bluebird plates, but only 60 percent of the money from elk and trout plates - 10 percent of the money from elk plates supports wildlife disease monitoring and testing programs (to benefit the livestock industry) and 10 percent from cutthroat plates supports non-motorized boat access.
Incidentally, in 2014, the Idaho Legislature denied the Department of Fish and Game the ability to add new plates or even to change the name of the elk and cutthroat plates (very specific) to wildlife and fish plates, a move that would have allowed for changing images occasionally and generating more revenue. It would seem that they believe that we Idahoans don't want a well funded wildlife program. Go figure.
Donate part of your tax return to support wildlife in Idaho!
On the second page of the Idaho Individual Tax form 40 you have the opportunity to donate to the “Nongame Wildlife Conservation Fund”.
Check-off this box on your next return or ask your tax preparer to mark the Nongame check-off on your behalf.
If you are not from Idaho, check with your own state wildlife agency about how you can help. Many states have a similar program.
"WOW. What a phenomenal piece you wrote. You are amazing." Jennifer Jackson
That is embarrassing but actually a fairly typical response to my nature essays. Since The Best of Nature is created from the very best of 16 years of these nature essays published weekly in the Idaho Falls Post Register (online readership 70,000), it is a fine read. It covers a wide variety of topics including humorous glimpses of nature, philosophy, natural history, and conservation. Readers praise the style, breadth of subject matter and my ability to communicate complex and emotional topics in a relaxed and understandable manner.
Everyone can find something to love in this book. From teenagers to octogenarians, from the coffee shop to the school room, these nature essays are widely read and enjoyed.
Some of the essays here are my personal favorites, others seemed to strike a chord with readers. Most have an important message or lesson that will resonate with you. They are written with a goal to simultaneously entertain and educate about the wonderful workings of nature. Some will make you laugh out loud and others will bring a tear to the eye and warm your heart.
"You hit a home run with your article on, Big Questions in Nature. It should be required reading for everyone who has lost touch with nature...great job!" Joe Chapman
"We enjoyed your column, Bloom Where Planted. Some of the best writing yet. The Post Register is fortunate to have your weekly columns." Lou Griffin.
To read more and to order a copy, click here or get the Kindle version
Copies are also available at:
Barnes and Noble in Idaho Falls
Perfect Light Photo Supply
Museum of Idaho
Valley Books, Jackson Wyoming
Avocet Corner Bookstore, Bear River National Wildlife Refuge, Brigham City, Utah
Craters of the Moon National Monument Bookstore, Arco, Idaho