As Sailboat already said, increasing the humidity a bit may help all the way around in-general, but as for eggs, if you're talking about fertile eggs that you want to hatch, then YES, HUMIDITY IS A HUGE DEAL!!! This is exactly why commercial egg incubators have different settings for temperature and humidity levels, and also this is effected by whether or not the incubator has a circulation fan or not, because there are different temperature and humidity levels for eggs of each different species, and if there is a circulation fan the temperature and humidity will be the same around the entire egg, while incubators that don't have a circulation fan tend to have the temperature be only on the apex of the egg, therefore the eggs must always be turned/rotated, where as they don't need to be if the incubator has a circulation fan...
But if you're simply talking about letting a breeding-pair incubate fertile eggs in a nestbox or cage, then you need to look-up the ideal humidity for the specific species of parrot the eggs are, and adjust the humidity in the nest-box/cage accordingly, because improper humidity is one of the main reasons that fertile eggs fail to hatch, right up there with improper temperature.