Then, I saw movement around her feet and heard a high pitched whistle.
Finally, I realized that three kittens were walking under her paws.
I didn't realize that the mother mountain lion had a serious looking wound on her left hind limb until I looked at the footage on my computer screen (you can barely see the wound in the second photo above and it is clear in the video). That made me so very sad. I hope that she makes it. Her kittens certainly won't make it if she is unable to hunt. On the bright side, she didn't appear to be limping.
The video made me realize how hard "herding cats" is. This mother was trying very hard to herd her kittens and keep them together. Her high pitched vocalizations help her with that tough job.
For comparison, here is another mountain lion walking in exactly the same spot days later. This lion has a normal amount of bulk.
The timing is about right for the "amorous mountain lion pair" who we observed back in June to be the parents of these kittens. You might remember this pair at a water hole together, and the female telling the male to back off while she had a drink.
Gestation is about 3 months. The kittens are born in a den and stay there for the first 6 weeks of their lives. After that, their mother takes them out into the world... and I suspect that the kittens in the video haven't been out of the den for very long. If you're interested, there's a great article about mountain lion kittens.
Here is the video. It starts with a quick flashback to late June when the parents were together and then quickly fast-forwards to the kittens. Be sure to have your volume turned on.