▁spent ▁more ▁than ▁ 2 0 ▁years ▁assemb ling ▁one ▁of ▁the ▁largest ▁collections ▁of ▁pure bre d ▁b ison ▁on ▁the ▁continent ▁( by ▁the ▁time ▁of ▁All ard ' s ▁death ▁in ▁ 1 8 9 6 , ▁the ▁her d ▁number ed ▁ 3 0 0 ). ▁In ▁ 1 9 0 7 , ▁after ▁U . S . ▁authorities ▁decl ined ▁to ▁buy ▁the ▁her d , ▁Pablo ▁struck ▁a ▁deal ▁with ▁the ▁Canadian ▁government ▁and ▁sh ipped ▁most ▁of ▁his ▁b ison ▁north ward ▁to ▁the ▁newly ▁created ▁El k ▁Island ▁National ▁Park . ▁Also , ▁in ▁ 1 9 0 7 , ▁the ▁New ▁York ▁Zo ological ▁Park ▁sent ▁ 1 5 ▁b ison ▁to ▁W ich ita ▁Mountains ▁Wild life ▁Ref uge ▁in ▁Oklahoma ▁forming ▁the ▁nucle us ▁of ▁a ▁her d ▁that ▁now ▁numbers ▁ 6 5 0 . ▁ ▁The ▁Y ellow stone ▁Park ▁B ison ▁H erd ▁formed ▁naturally ▁from ▁a ▁few ▁b ison ▁that ▁remained ▁in ▁the ▁Y ellow stone ▁Park ▁area ▁after ▁the ▁great ▁sla ugh ter ▁at ▁the ▁end ▁of ▁the ▁ 1 9 th ▁century . ▁Y ellow stone ▁National ▁Park ▁is ▁one ▁of ▁the ▁very ▁few ▁areas ▁where ▁wild ▁b ison ▁were ▁never ▁completely ▁ext ir p ated . ▁It ▁is ▁the ▁only ▁continu ously ▁wild ▁b ison ▁her d ▁in ▁the ▁United ▁States . ▁Number ing ▁between ▁ 3 , 0 0 0 ▁and ▁ 3 , 5 0 0 , ▁the ▁Y ellow stone ▁Park ▁b