The nutritional stress hypothesis formulated by Nowicki et al. (1998) is based on the findings that brain structures underlying song learning in songbirds largely develop during the first few months post-hatching; a period when nestlings are most likely to suffer nutritional and other stresses that can have detrimental and lasting effects on the expression of song behaviour in close-ended learners. However, some bird species are considered to be open-ended learners, meaning that they have the ability to acquire and develop new songs every spring. Song acquisition throughout adulthood could compensate for any deficits due to stress during early development. I therefore tested the nutritional stress hypothesis by supplying mealworms to a group comprised of yearling and adult male pied flycatchers (Ficedula hypoleuca) during the breeding season of 2007. Song repertoires and song rates were of equal size in experimental males and controls prior to experimentation.