In the 17 photos of adult male bison I took in Yellowstone National Park in spring and fall of 2017, only one (6 percent) had a normal length bilateral scrotum. All male bison used to have a long, very visible scrotum with the testes side by side (bilateral). Male bison with ectopic testes and no visible scrotum were in 35 percent of the photos, 7 times what is supposed to raise a red flag for a birth defect. No scrotum is a very serious birth defect on a male mammal!
The scrotums on the rest of the photographed bison (59 percent) were formed with the left half of the scrotum directly forward of the right and many were abnormally short.
Oddly, park biologists don't seem to notice many of the large adult male bison that walk by them every day have no visible scrotum or have a scrotum that is totally weird-looking.
According to Centers for Disease Control records, genitourinary disorders on newborn male humans have increased significantly since 2001. I would think that health officials would be concerned enough to insist we find what is causing the epidemic of extremely serious reproductive birth defects on bison and other mammals. Wouldn't you?