Previous studies found that complex social environment increases new neuronal recruitment in brains of adult male zebra finches, in comparison with exposure to a simple social environment. These experiments could not determine, however, whether this increase was due to greater amounts of auditory input (amount of auditory information the male is exposed to), or auditory output (amount of song it produces). To answer this question, we raised male zebra finches to adulthood in a controlled environment, and were then exposed them to either a single unfamiliar female (simple social environment) or to 45 unfamiliar zebra finches of both sexes (complex social environment). Their singing behavior was monitored in these new social environments. Birds which were exposed to a simple social environment sang significantly more than birds which were exposed to a complex social environment. This supports the hypothesis that increased neuronal recruitment in birds exposed to a complex social environment correlates with processing and storing of auditory input, and not with song produced by the bird.