Deer in the Dark - UPDATE February 2, 2019

In my old deer research days, it was hard to walk with deer 24 hours because they see well enough to keep active at night when I needed a flashlight to do the best I could. DeerDeer in the darkTheir eyes are big, and when the pupil is as open as on this deer, they can let a lot of light in. Bears eyes are much smaller and can’t open nearly so wide. They mostly sleep through the night and are most active when it is light enough to use their cones for color vision when picking berries, etc. Around human development, some bears become nocturnal and can see well enough to find garbage, etc., with the help of their nose, their tapetum lucidum, and rods which greatly aid night vision. The tapetum lucidum is a reflector in the back of the eye that reflects light back over the retina to give the photo receptors a second chance to form an image at low light levels. Some of the light is reflected back out the pupil, creating the eye shine we see in bears and deer and any other vertebrate that has this reflector. Rod cells are sensitive to light and aid non-color vision in low light. Cones are sensitive to color but require more light to be effective. Deer have many more rods than cones, giving them excellent night vision.

The big ears of deer and bears are their first line of defense against danger. They gather more sounds than small human ears can, and they can hear higher sounds. Like humans, deer hear best in moderate frequencies between 4,000 and 8,000 hertz. To an extent, they can hear into the upper registers up to 30,000 hertz. People can only hear up to 20,000 hertz when they are young, with the limit dropping into the 15,000 to 17,000 hertz range by middle age. I don’t know what the limit is for bears, but they can hear higher frequencies than people can. For example, they can hear dog whistles that are in the 23,000 to 54,000 hertz range, which is beyond the 20,000 hertz limit of people of all ages. Dogs and cats can hear higher pitched sounds than deer can. Dogs can hear up to 45,000 hertz and cats up to 64,000 hertz, according to what I’ve read.

On another subject, I had received a nice message from the producer of the Mississippi River documentary series, thanking me for “for providing access to the charismatic black bear family working out the hibernation question — to emerge, or not to emerge! That was a highlight of the series.” I say thank you for showing bears in a good light, and it was fun working with cameraman Neil Rettig, who is a very experienced cameraman who I worked with on another worldwide film in an effort to get bears out to the public in a good light over 40 years ago.

It is all part of our mission “to advance the long-term survival of bears worldwide by replacing misconceptions with scientific facts about bears, their roles in ecosystems, and their relations with humans.” That is something the readers of these updates are working to do, too, and it is part of what I mean when I say: Thank you for all you do.

Lynn Rogers, Biologist, Wildlife Research Institute and North American Bear Center

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