Nest box ventilation may be crucial to maintain healthy conditions for Little Owl egg and chick development. We investigated whether it matters in which way ventilation is provided. Eight different nest boxes were tested, using relative humitidy (RH) and temperature data loggers. The mere presence of any kind of ventilation sufficed to obtain the maximal reduction of RH compared to a non-ventilated nest box. Under high ambient RH, problems arising from high humidity may persist despite the presence of ventilation.