something that gives an earlywarningofdangerorfailure, in the way that, in the past, acanarytaken into amine(= anundergroundplacefordiggingcoalorminerals)woulddieif theairwas notsafetobreathe,warningthepeopleworkingthere:
TheArctichas been called thecanaryin a coalmine when it comes toglobalwarming.
He likensbutterfliesto thecanaryin the coalmine, being the first tosufferwhen theenvironmentis understress.
Thecanaryin the mine is theairport. Aslongasitsusageis down,hotelusageand thelocaleconomywill be down.