9 6 0 ▁and ▁ 1 9 8 0 . ▁Ev idence ▁from ▁a ▁question naire ▁in ▁ 2 0 0 5 ▁and ▁ 2 0 0 6 ▁also ▁supported ▁an ▁on going ▁decl ine , ▁with ▁almost ▁half ▁of ▁~ 2 0 , 0 0 0 ▁participants ▁in ▁P T ES ' ▁Hog watch ▁survey ▁reporting ▁the ▁impression ▁that ▁there ▁were ▁fewer ▁h edge h ogs ▁than ▁there ▁were ▁five ▁years ▁earlier . ▁ ▁A ▁review ▁of ▁the ▁available ▁survey ▁data ▁for ▁the ▁population ▁tr end ▁of ▁the ▁h edge h og ▁in ▁Britain ▁was ▁undert aken ▁by ▁the ▁British ▁Trust ▁for ▁Or n ith ology ▁( B TO ) ▁in ▁a ▁report ▁commission ed ▁by ▁P T ES ▁and ▁the ▁British ▁H edge h og ▁Pres ervation ▁Society ▁( B HP S ). ▁This ▁concluded ▁that , ▁at ▁a ▁conserv ative ▁estimate , ▁ 2 5 % ▁of ▁the ▁British ▁h edge h og ▁population ▁had ▁been ▁lost ▁in ▁a ▁de cade . ▁The ▁report ▁also ▁highlight ed ▁the ▁importance ▁of ▁long - term ▁monitoring ▁to ▁provide ▁datasets ▁with ▁sufficient ▁power ▁to ▁allow ▁the ▁changes ▁to ▁the ▁population ▁to ▁be ▁identified . ▁Currently , ▁the ▁most ▁important ▁monitoring ▁program mes ▁involved ▁in ▁collect ing ▁information ▁about ▁the ▁status ▁of ▁the ▁British ▁h edge h og ▁population ▁are ▁P T ES ’ ▁M amm als ▁on ▁Ro ads ▁and ▁Living ▁with ▁M amm als ▁surve ys , ▁and ▁the ▁B TO ▁Bre eding ▁Bird ▁Survey ▁and ▁Garden ▁Bird Watch ▁survey . ▁A