Yesterday some Pronghorns came so close to the vehicle that I had two choices; 1. grab the back up D200 with the Nikkor 18-200mm VR lens attach and photograph the Pronghorn with it or, 2. Use the D300 with the 200-400mm VR + 1.4x TC attached and do close-ups. Since I have many fully body images I decided to do close-ups and I am glad that I did. The image above is 100% full frame and I was barely able to get the tips of the ears of the buck to fit.
The Pronghorn rut season is over and the pronghorns are in the process of replacing the outer sheathing on their horns. The horns of Pronghorns are composed of a permanent slender, laterally flattened blade of bone that is covered by a keratinous sheath that grows around the bony core that is shed and regrown annually.
In the image above the flattened blades of bone can be seen at the tips, notices how slender the horns are there. The hair-like keratin regrowth begins at the base of the horn and moves towards the tips. I find it fascinating that in this frame the hair-like keratin is plainly visible where the horns are regrowing and that it also shows the regrowth process is not yet complete.
Keratin is the substance that human hair and fingernails are composed of.
This image shows a buck before the outer sheath has been shed, notice that his horns are relatively smooth, slightly shiny at the tips and show no signs of being “hairy”.
Pronghorns are the only North American mammal that retain their horns yet shed and replace the outer sheath annually.