When photographing in snowy conditions, the majority of the composition is pure white, so your DSLR, film camera, and/or mirrorless camera meter is going to make the snow middle grey, and if you trust your camera meter, you will be underexposed the majority of the time when shooting white on white. Most photography instructors will teach you to use exposure compensations and open by 1 stop to 2 stops, to adjust for the expected underexposure resulting from the meter’s reading when photographing in snowy conditions. Personally, I recommend compensating manually with the command dial, checking your histogram for exposure "as I do," 99% of the time; I don't enjoy fiddling with my camera settings in the field or trying to rely on the display or viewfinder to view my images and see if the exposure is correct. I am focused on the subjects I am photographing and not my camera; my camera is just my medium an extension of my visual artistry. I don't want to think about my gear in the field; wildlife photography is similar to sports photography. A lot is going on around us, and if we are thinking too much and trying to figure out our settings in the field, our wildlife will more than likely be gone. Today's cameras are getting better. Soon, we will have more accurate displays, such as my Nikon Z7 Mark ii, D6, and D850 which have much more accurate displays than my D810 or previous digital cameras. And if your image is a little dark in the snow, that is okay; with today's digital camera sensors, ranging from 20 to 100 megapixels, we can easily lighten a darkened image when editing on our computers and software by 1 - 5 stops, without affecting the quality of our image. Overexposing runs the risk of blowing out the highlights, and possibly your subject will have little or no details making your image unusable, so a little darker in the snow to keep the detail is my rule of thumb.
When first-time clients join my Hokkaido winter Japan nature tour expedition workshop, I like to take a moment to discuss photographing Hokkaido wildlife in the snow. When I have a friend or client often checking the back of their camera in the field, I know they are having difficulties photographing in the snow, so this is my cue to shoot together, giving them my settings under my breath. If time permits, I prefer to retake ten minutes and explain how to properly set the exposure for white on white so my friends and clients will never run into the problem again. My camera settings for small, alert birds are 1/2500s to 1/5000s, f8 - f7.1, and if the lighting is low, I have been known to stop up to f4, but this is rare for me. For big birds, I choose f11, so the entire bird will be in focus, such as the Red-Crowned Crane Tancho, which stands at 150 - 158 cm (4 ft - 5 ft) tall, weighing 8 - 11 kg (17 - 25 pounds) with a huge wingspan measuring 200 to 260 cm (6.5 ft to 8.5 ft). ISO I adjust manually according to my shutter and f-stop preferences for the shoot.