▁receiver , ▁en abling ▁accurate ▁positions ▁to ▁be ▁broadcast ▁at ▁regular ▁intervals , ▁but ▁these ▁are ▁in ev it ably ▁heav ier ▁and ▁more ▁expensive ▁than ▁devices ▁without ▁G PS . ▁An ▁alternative ▁is ▁the ▁Arg os ▁Do pp ler ▁tag , ▁also ▁called ▁a ▁' Platform ▁Trans mit ter ▁Terminal ' ▁( PT T ) ▁which ▁sends ▁regularly ▁to ▁the ▁polar - or bit ing ▁Arg os ▁sat ell ites ; ▁using ▁Do pp ler ▁shift , ▁the ▁animal ' s ▁location ▁can ▁be ▁estimated , ▁relatively ▁roughly ▁compared ▁to ▁G PS , ▁but ▁at ▁lower ▁cost ▁and ▁weight . ▁ ▁Radio ▁tracking ▁tags ▁can ▁be ▁fitted ▁to ▁insect s ▁including ▁drag on f lies ▁and ▁be es . ▁ ▁In ▁culture ▁ ▁Before ▁animal ▁migration ▁was ▁understood , ▁various ▁fol kl ore ▁and ▁err one ous ▁explan ations ▁spr ang ▁up ▁to ▁account ▁for ▁the ▁disapp earance ▁or ▁sudden ▁arrival ▁of ▁birds ▁in ▁an ▁area . ▁In ▁An cient ▁Greece , ▁Arist ot le ▁proposed ▁that ▁rob ins ▁turned ▁into ▁red starts ▁when ▁summer ▁arrived . ▁The ▁bar n acle ▁go ose ▁was ▁explained ▁in ▁European ▁Med ieval ▁best i aries ▁and ▁manuscript s ▁as ▁either ▁growing ▁like ▁fruit ▁on ▁trees , ▁or ▁developing ▁from ▁go ose ▁bar n acles ▁on ▁pieces ▁of ▁dr ift wood . ▁Another ▁example ▁is ▁the ▁sw allow , ▁which ▁was ▁once ▁thought , ▁even ▁by ▁natural ists ▁such ▁as ▁Gilbert ▁White , ▁to ▁hibernate ▁either ▁under water , ▁buried ▁in ▁mud dy ▁river b anks