 The clutch was described as consisting of a single egg ; given the bird 's large size , this led to proposals that the solitaire was K @-@ selected , which means it produced a low number of altricial offspring , which required extensive parental care until maturity . The gathering of unrelated juveniles suggests that they formed crèches , that may have followed foraging adults as part of the learning process . A study of subfossil remains found that the carpal knob only developed after the bird reached skeletal maturity . 
