Magnetoception fascinates me.When I used to fish regularly I noticed if I was happy and blissy unmoving the sparrows would sometimes take maggot from my knees and shoes.If i was stressed still unmoving couldn't get them near me.With birds recognised awareness of magnetic fields was your blackbird picking up on your field, did you improve the birds song with an eventual better mood to his warble.If he is happier bet he is not so fat these days either ;-)Seagulls don't seem to operate quite the same way like most of us they have prob lost the skill,just winged hooligans all the chips n junk food they eat I would guess.If you look at a seagull squint your eyes they wear back to front baseball caps..