Answered by Idaho Fish and Game biologist
Pronghorn are quite a unique species. They grow horns that shed annually unlike other species that grow horns that get larger each year like bighorn sheep and mountain goats.
Horns are different than antlers. Horns are made from a keratinous sheath that grows from a core of live bone tissue. In bighorn sheep, horn is added to each year. In pronghorn, the horn is shed each year similar to antlers. Antlers are in fact a porous fast growing bone tissue that are grown annually by the males of the species and are fed by a “velvet” tissue that is highly vascularized and feeds the rapid growth of the bone.
A pronghorn’s horn does not necessarily get larger each year and tends to top out between age 2-6. Nutrition and moisture seem to have influence on antler and horn growth as does genetics. The female also has a horn that grows similarly to the males, but is usually smaller. The male’s horns are shed from October through December after the rut and are shed when new horn begins to grow underneath. The new horn is typically complete by late winter or early spring. Females tend to shed their horns in mid-late summer, but sometimes they can be more variable and collect stacked horns (like paper cups) over 2-3 years. https://idfg.idaho.gov/questions
Pronghorn are able to run up to 65 mph, making them the fastest animal in North America and second only to the cheetah. But cheetahs are sprinters and the pronghorn is an endurance runner. Herds of pronghorn galloping across the desert can average 40 miles an hour for half an hour or more. If a pronghorn ran a marathon, it would complete the 26.2 mile course in 40 minutes or so.
Pronghorn rely not only on speed but also keen vision for protection. Their eyes, as big as an elephant’s, see the world as you would if using binoculars with 8 power magnification.
The size of eye is important because the larger the eye, the larger the image on the retina. Imagine watching a 12-inch television screen compared with a 36-inch screen. Bigger eyes have more light receptors in the same way that larger TV screens have more pixels, and hence a better image.
How the Eyes Work
All the different parts of your eyes work together to help you see.
- Light passes through the cornea.
- Some of this light enters the eye through an opening called the pupil.
- Light passes through the lens (a clear inner part of the eye). The lens works together with the cornea to focus light correctly on the retina.
- Light hits the retina, which is a thin layer of tissue that lines the back of the eye on the inside. Special cells on the retina called photoreceptors turn the light into electrical signals.
- Electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.
See the Blood Vessels in You Retina
Materials: mini flashlight, darkened room, sheet of black construction paper, eye protection such as goggles with clear lenses (recommended)
- Darken the room. Turn off the lights and close the shades, if possible. Dim light or ambient light is fine.
- Put on eye protection or goggles, if using.
- In one hand hold the black sheet of construction paper in front of your face so that the paper fills your field of view.
- In the other hand, hold the mini flashlight in front of one eye, about ½ inch in front of and slightly below the center of the pupil. Be careful not to poke yourself in the eye!
- Turn the flashlight on and move it slowly from side to side a short distance, about a ¼ inch. Do not move your eye or follow the motion of the light.
- Keep doing this for 20 seconds. Notice the pattern that appears. It will look like the branches of a tree.
You can use a dim point of light to cast a shadow of the blood supply of your retina. This will allow you to see the blood supply of your retina, and even your blind spot. The pattern you see are the arteries and veins that supplies blood to your retina. It spreads out from the an area on the retina without photoreceptors called your blind spot.