Introduced newly hatched and 8-day-old squabs to 65 pairs of experienced ring dove foster parents after 13 days of incubation. Results indicated greater responsivity by the foster parents to newly hatched squabs (as measured by crop weights of the foster parents and weight gain of the squabs) as compared to older squabs. In addition, it was found that with repeated introduction of newly hatched squabs, squab weight gain decreased, although a corresponding decrease in crop weights was not obtained in all cases. (PsycINFO Database Record (c) 2006 APA, all rights reserved)