This sounds a little like Marilyn vos Savant's golden pancake puzzle. I never fully wrapped my head around the logic on that one, but here's an attempt at applying it to this one.
The toad you're looking at has a 1 in 2 chance of being a male.
Of the two behind, one of which croaked and announced himself as a male, there are these possible arrangements:
M=the male that croaked
m=a second, bonus male
Toad 1 Toad 2
So picking either of the two would have a 3 in 4 chance of success.