Bulletin No. 11 of National Geographical Society of India Banaras

A suitable legend giving the address of the ringer and the serial number of the bird is embossed on or punched into the ring.r 1 Such places as lie in the path of the migration routes of the birds are naturally more suitable than others for the study of migration. [...] What is the nature of the trigger the pressing of which is the immediate cause of migration ? Fine weather is certainly one of the causes which releases the pent up forces of the migratory instinct. [...] The position to-da is roughly this : The birds leave their winter quarters in spring as a result of the increase in the size of the sex-glands ; the decrease in the size of these glands causes them to leavo their summer quarters where they had bred. [...] f. is proportionate to the length of the conductor to the speed of travel and to the effective local strength of the earth's magnetic field. [...] In other. words the transported object will suffer a deflection or 'drift' to the right in the northern hemisphere and to the left in the southern ( Ferrel's Law ). The drift is zero at the equator and maximum at the poles.