In slovak language, the word "vták" (bird) can be sometimes used as slang for male reproductive member. Also rooster has a certain different name. And as TwoGunAngel noted, most bees are female (and you probably don't get to see drones that much often). Therefore I think birds are supposed to represent males and bees are supposed to represent females.
So fixed: Time to explain to Yotsuba about the bees and the other bees.