More of these frogs find ways to escape than you can imagine. I have used a fine mesh material to cover the areas of my tank that are not covered by the glass and light fixtures. The above photo shows some difference in the frogs. Males usually have black markings on their arms and will be somewhat smaller. However, do not depend on size alone to determine.
Males are usually the vocal ones as well.
There are some documented facts on their ages while in captivity located here. Yes the males will sometimes be heard calling or vocalizing in the evenings. Yes they can see. These frogs are very friendly towards one another. The reason is the african clawed will make a meal out of your smaller african dwarf.