In captivity, novel selective pressures can lead to divergence from the wild source population, which can be a liability for animals released into the wild. Easily measured indices of change, like body mass, might be important for early detection of adaptation to captivity. We hypothesised that for species subject to long-term captive breeding, body mass may be a useful proxy for detecting morphological adaptations to captivity. We test this (and alternative explanatory variables) with 22 years of pedigree data on Orange-bellied Parrots Neophema chrysogaster and predict that adult body mass would change over successive generations in captivity. The best model of adult body mass showed a relationship with maternal effects both directly (heavier mothers produced heavier offspring) and indirectly (different founding maternal lineages produced heavier or lighter descendants), plus circumstances in the year of birth (e.g. years with better food quality produced heavier birds). Body mass did not change with increasing generations of captive breeding. Our results suggest that either adaptation to captivity has not occurred or, if it has, body mass is too coarse an index to detect it. Captive breeding programmes should directly measure traits of interest and ideally compare these to traits of wild birds to identify an ideal morphological baseline.