There was some very neat looking ice in Yellowstone. Below is a photo of ice crystals near a hot spring in West Thumb. You can see the green growth under the ice crystals. Animals eat the greenery year round, but apparently it contains high levels of arsenic and other bad things so the animals who graze on it have easier, but shorter, lives. Interesting. I like the photo because of the amazing contrasts, and because the frost is so big and so defined that it looks like white leaves on the ground, or a frost plant.
The other photo, what looks sort of like frozen angel hair, is called needle ice. It forms around geothermal formations because the moisture in the ground freezes and pushes up out of the ground in small, thin strands and small bunches. It is also like an ice plant springing from the frozen ground. Amazingly cool.
We saw a glimpse of an otter in one of the warm patches of Yellowstone lake, but only for a moment - no photos. We saw Bald Eagles this trip too, and a golden eagle, but again, no photos, sorry.
We saw lots of geothermal features while hiking in snowshoes, and also at some stops along the journey in the snow coach. It was not at all crowded in the park. We did run into some snowmobile groups, but not that many. Although I like to snowmobile on groomed and designated trails in non-wildlife areas, I think it's shame and wildly inappropriate to allow snowmobiles in the National Park, among the wildlife. They are very loud and disruptive not only to the animals, but to anyone else around. I know it's a big controversy, but since there are so many other places to snowmobile I don't see why there should be so much insistence it take place in Yellowstone.
In any event, lots of way cool stuff to see in winter so it's a very nice trip to make.