▁red ▁upper ▁mand ible ▁with ▁a ▁yellow ▁tip , ▁while ▁the ▁lower ▁mand ible ▁is ▁black . ▁The ▁females ▁have ▁an ▁all - black ▁be ak . ▁ ▁Im m ature ▁Lord ▁Derby ' s ▁par ake ets ▁are ▁d ull er ▁in ▁colour ▁than ▁the ▁adult s . ▁Ju ven ile ▁birds ▁have ▁green ▁crow ns , ▁orange - red ▁upper ▁and ▁lower ▁mand ible ▁( be ak ), ▁and ▁their ▁ir ises ▁are ▁dark ▁and ▁do ▁not ▁light en ▁until ▁they ▁reach ▁m atur ity ▁between ▁two ▁and ▁three ▁years ▁of ▁age . ▁ ▁Sex ual ▁dim orphism ▁ ▁Re production ▁ ▁Bre eding ▁season ▁usually ▁begins ▁between ▁April ▁and ▁June . ▁The ▁female ▁l ays ▁a ▁cl utch ▁of ▁two ▁to ▁four ▁eggs ▁() ▁in ▁nest ▁holes ▁of ▁trees . ▁The ▁young ▁h atch ▁after ▁an ▁inc ub ation ▁period ▁of ▁about ▁ 2 3 ▁days ▁and ▁will ▁f ledge ▁after ▁ 8 ▁to ▁ 9 ▁weeks . ▁ ▁References ▁ ▁External ▁links ▁World ▁Par rot ▁Trust ▁Par rot ▁Encyclopedia ▁- ▁Species ▁Pro files ▁Lord ▁Derby ' s ▁par ake ets ▁in ▁capital ▁of ▁Tib et ▁Derby an ▁pictures ▁and ▁links ▁Bird Life ▁Species ▁Fact sheet ▁Oriental ▁Bird ▁Im ages : ▁Derby an ▁par ake et ▁▁ ▁Selected ▁photos ▁ ▁http :// an imal - world . com / ency clo / bird s / par ake ets / Der by an Par ake et . php # ▁ ▁http :// home . wan ado o . nl / ps