Oster egg cookers are designed to cook eggs in the size range of standard hen eggs; it is not therefore optimal to use them for other sizes of egg. However, cooking other birds' eggs may be feasible if done with caution and regard to the size of egg.
Duck eggs, for example, can be found in sizes only slightly larger than the largest hen eggs. An Oster egg cooker could handle this size of egg if the water fill is increased. This increase the cooking time appropriately. Similarly, bantam eggs can be cooked by reducing the water fill to a lower level.