▁S ands , ▁East ▁R iding ▁of ▁York shire . ▁ ▁Population ▁tr ends ▁The ▁population ▁for ▁the ▁western ▁Pale ar ctic ▁is ▁estimated ▁at ▁ 3 5 , 0 0 0 – 5 0 , 0 0 0 ▁pairs . ▁The ▁global ▁population ▁is ▁unknown ▁and ▁could ▁be ▁anything ▁between ▁ 1 5 0 , 0 0 0 ▁and ▁ 2 0 0 , 0 0 0 ▁individuals ( B ird life ▁International , ▁ 2 0 0 4 ). ▁This ▁uncertainty ▁is ▁due ▁to ▁the ▁fact ▁that ▁most ▁of ▁the ▁world ' s ▁population ▁is ▁situated ▁in ▁Russia ▁and ▁former ▁Soviet ▁republic s ▁where ▁it ▁is ▁not ▁quant ified . ▁ ▁The ▁evolution ▁has ▁been ▁par ado x ical ▁throughout ▁the ▁ 2 0 th ▁century . ▁In ▁the ▁beginning ▁of ▁the ▁century ▁up ▁to ▁the ▁ 1 9 4 0 s , ▁during ▁a ▁period ▁when ▁other ▁ra pt ors ▁greatly ▁decre ased ▁because ▁of ▁human ▁per sec ution , ▁the ▁Mont agu ' s ▁har rier ▁actually ▁increased ▁its ▁population ▁and ▁bre eding ▁range , ▁bre eding ▁for ▁the ▁first ▁time ▁in ▁Den mark ▁in ▁the ▁ 1 9 0 0 s , ▁and ▁greatly ▁increasing ▁elsewhere . ▁However , ▁from ▁the ▁ 1 9 4 0 s ▁on wards ▁it ▁has ▁decre ased ▁rapidly . ▁This ▁is ▁due ▁to ▁several ▁negative ▁factors : ▁first , ▁the ▁massive ▁use ▁of ▁agricult ural ▁p estic ides ▁such ▁as ▁D DT ▁and ▁other ▁environmental ▁po isons ▁was ▁extremely ▁det r iment