You assume that the birds detect infrasound with their ears. Elephants hear infrasound with the pads of their feet: https://www.dw.com/en/biodiversity-poaching-

You assume that the birds detect infrasound with their ears. Elephants hear infrasound with the pads of their feet: https://www.dw.com/en/biodiversity-poaching-africa-asia-nature-wildlife/a-62564160 https://www.dw.com/en/biodiversity-poaching-africa-asia-natu... Of course, birds in flight can't feel the ground vibrate, but I wouldn't immediately eliminate alternatives like infrasound making the birds' feathers vibrate.