Birdo!
You ought to know by now that yoshis lay eggs all the time, especially males!
Those eggs are used for protection of themselves and other yoshis/creatures!
In order to produce offspring, those eggs has to be... er... fertilised!! Much the same way done like birds or reptiles, and we know that science proved that those real-life creatures reproduce sexually.
I am a pure Super Mario lover!!
...and in no point in the future will he ever be abandonded by me!
I will even drawn the best Super Mario comics ever to exist!!