toadschooled:

Not all toads exhibit obvious sexual dimorphism, but when it comes to breeding Yosemite toads [Anaxyrus canorus, formerly Bufo canorus] don’t have time to waste with uncertainty. Females have significantly darker patterning than males, a trait that helps the two identify each other during the brief period of summer snow melt in which they can reproduce. Images by Californiaherps.com and Wikipedia Commons.