Like all breeding frogs, toads will jump on anything that comes close. I've seen them following turtles, even birds! I also watched this morning as one lone male saw movement and jumped... onto the back of a mating pair which promptly sank. he resurfaced (and so did they later), and jumped on this toad (middle) at the same time as another male did. I assume the toad in the middle is female, but not sure. Usually the males are much smaller, so possibly, although male toads will mistakenly jump on other males if they sense them moving nearby. Better to jump first and discover your mistake after rather than let a female get away, I guess.