Asked by: Steven Jenkins, Bognor Regis
A bird’s wing feathers are mounted like slats on a venetian blind. They only lock together to form a solid aerofoil against airflow from below. If they fly upside down, the feathers rotate open and let the air through. But geese do use a manoeuvre called ‘whiffling’ where they roll their body upside down and twist their neck to keep their head the right way up. This lets them rapidly lose speed and height for a fast landing.