Though my certainty has varied a great deal over the past few months, I am now pretty certain we are likely to see some new bison calves this month. In the following video two signs of future calving are present: springing, and swelling udders. When a female cow or bison is pregnant the ligaments around the vulva become relaxed which causes it to bounce or "spring" when the animal moves. I've seen springing among the bison females for a few months now, but in the last few weeks I've also started to see swelling teats. Today, after a week's absence from the ranch, I returned to observe that among several of the females the tissue above the teats (which contains the mammary glands) is also enlarged.
For comparison I'm including a photograph (below), taken today, of a different female bison without swollen udders. The teats are barely visible even when the image is enlarged.
