Adults are brown on the upperparts and pale on the underparts, with heavy streaking throughout. They have short forked tails. Their bills are conical like most finches but are more elongated and slender than those of other co-occurring finches.
Fun Fact Pine Siskins can temporarily store seeds totaling as much as 10% of their body mass in a part of their esophagus called the crop. The energy in that amount of food could get them through 5–6 nighttime hours of subzero temperatures.