What is a distinguishing feature of bighorn sheep?

Bighorn sheep are particularly noted for their large, curling horns, which are a distinctive feature of the species. These impressive horns can grow significantly and are prominently displayed on mature males, creating a striking silhouette against their natural habitat. The size and curl of the horns are not only visually striking but also serve practical purposes; they are used in combat during mating displays and can indicate the health and age of the individual.

In contrast to colorful coats or urban habitation, which do not specifically apply to bighorn sheep, the horns are a critical characteristic that sets them apart from other sheep species. The option regarding having no horns is inaccurate as bighorn sheep males (rams) are well-known for their impressive horns, while females (ewes) also possess smaller but still notable horns. Thus, the defining feature of large, curling horns is what makes this answer correct.