▁dig estion ▁of ▁plant ▁material . ▁However , ▁the ▁rocks ▁apparently ▁sw allowed ▁by ▁this ▁spec imen ▁are ▁much ▁larger , ▁co ar ser , ▁and ▁less ▁numerous ▁than ▁most ▁g ast rol ith s , ▁and ▁were ▁unlikely ▁to ▁have ▁been ▁used ▁for ▁the ▁same ▁purpose ▁as ▁those ▁sw allowed ▁by ▁her b iv ores . ▁Instead , ▁it ▁has ▁been ▁suggested ▁that ▁they ▁were ▁sw allowed ▁to ▁help ▁clean ▁the ▁dig est ive ▁tract , ▁a ▁usage ▁which ▁has ▁been ▁reported ▁in ▁living ▁birds ▁of ▁pre y ▁as ▁well ▁as ▁other ▁car n iv orous ▁animals ▁with ▁high - f at ▁di ets , ▁such ▁as ▁p inn ip eds . ▁The ▁description ▁of ▁this ▁spec imen ▁claimed ▁that ▁it ▁was ▁pla us ible , ▁but ▁uncertain , ▁that ▁Boh ai orn is ▁was ▁e colog ically ▁similar ▁to ▁birds ▁of ▁pre y . ▁ ▁However , ▁these ▁rocks ▁were ▁later ▁found ▁to ▁be ▁min eral ▁con cret ions , ▁probably ▁formed ▁from ▁the ▁same ▁min eral ▁as ▁the ▁foss il ▁spec imen . ▁Thus , ▁they ▁are ▁not ▁indic ative ▁of ▁di et . ▁ ▁Boh ai orn ith ids ▁had ▁foot ▁proport ions ▁which ▁were ▁between ▁those ▁expected ▁of ▁ar b ore al ▁and ▁terrest rial ▁birds , ▁but ▁their ▁long ▁cla ws ▁make ▁terrest rial ▁hab its ▁unlikely . ▁Nevertheless , ▁bo hai orn ith ids ▁lack ed ▁many ▁of ▁the ▁special ized ▁foot ▁features ▁which ▁allow ▁modern ▁birds ▁to ▁per ch ▁and ▁clim b ▁tree ▁tr unks