Which feature helps identify a trumpeter swan from other swan species?

The correct choice is based on two prominent features of the trumpeter swan: its long neck and all-white feathers. These characteristics help distinguish the trumpeter swan from other swan species, such as the tundra swan, which has a more varied coloration and a shorter neck in comparison. The long neck allows the trumpeter swan to have a more graceful silhouette when swimming or flying, and the all-white plumage is a key visual feature that makes it easily recognizable in its natural habitat.

While other features such as feather patterns and leg length may vary among swan species, the combination of a long neck with all white feathers is particularly defining for the trumpeter swan. These distinguishing traits assist birdwatchers and hunters alike in identifying this specific species in the field.