It has always struck me as odd (and difficult when trying to learn) how many birds have such an extreme difference between the sexes, and some others are to all extents and purposes totally indistinguishable. For example, cardinals are completely different colors between male and female. Most ducks look like a completely different species, they are colored so differently.
I encountered a pair of ospreys this past weekend and noted some very minor differences and intended to look it up when I got home to see if indeed I had stumbled upon an important differentiation. I saw that one of the birds had brown flecks on the white throat feathers.
Turns out the flecks did indeed indicate the female bird...... This was 2 or three minutes later:
I looked it up anyway when I got home and indeed those specks are present on the females. It's as if I was able to learn from observation, like science! (Or something.)