Photographing winter birds

Snow and cold weather bring some of the most unique wildlife photography opportunities, since most of wildlife have to concentrate their efforts on searching for food and enduring the severe weather. As eager as I am to photograph them, I am very careful in approaching them during these harsh times. I believe no image is worth putting wellbeing of my subjects in danger.
During the heavy snowstorm in early January, I located a spot in the field nearby my house where many birds feed on leftover gains. I sat my photo blind across the area. I didn’t have to wait long before more than 20 Northern Cardinals and a few dozens of various birds showed up.
The temperature was in minus with wind chill as low as -30F. All birds puffed up their feathers to keep the heat inside, which made them to appear bigger than they actually are. That’s why I always prefer photographing birds in early spring and winter.
When photographing something less than 18% gray especially snow, I overexpose by +1/2 to +1 depend on the subject. For a Northern Cardinal, I normally give +3/4 exposure, so it won’t blow too much highlight of the bird’s bright red feathers.