SONNEMANN & SJÖLANDER (1977) found that zebra finch females raised by their own species (Zz females) differ in mate preference from females raised by Bengalese finches (Zb females) when given the choice between a Z male and a B male. Their data also showed an own species bias (Zz females strongly preferred Z males, whereas Zb females showed about equal interest in Z and B males). Several authors mentioned the existence of a preference for species-specific characteristics independent of early experience (a so called 'innate' preference) as a cause for an own species bias. This conclusion can be doubted for theoretical and methodological reasons and the question for the processes leading to an own species bias in zebra finch females seems completely open. We investigated several possible causes of the own species bias. Our experiments suggest that the final preference in Z females may be influenced by three independent processes. First, visual stimuli are involved. Information on these seems to stem exclusively, or at least largely from parental influence. No initial preference for visual characteristics, independent of experience with Z or B has to be assumed. Second, experiments indicate that a preference for actively courting males is present. The process underlying this is unknown but seems independent of the one giving rise to a preference for visual stimuli. Third, during the period between raising and testing (during which the females were visually isolated) the preference changes with age. Here too, the underlying process is unclear. Several possible causes for this change are discussed. The process underlying it is probably different from the other two. Altogether the results indicate that the own species bias may be the result of several independent developmental processes, which in combination led to a bias in testing.