Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird

Many migrating birds rely on the Earth's magnetic field for their sense of direction, although what mechanism they use to detect this extraordinarily weak field is unknown. Following the surprise observation that night-migratory songbirds (European robins) tested between autumn 2004 and autumn 2006 in wooden huts on the University of Oldenburg campus seemed unable to orient in the appropriate migratory direction, Henrik Mouritsen and colleagues performed controlled experiments to establish what was happening. They find that robins lose the ability to use the Earth's magnetic field when exposed to low-level AM electromagnetic noise between around 20 kz and 20 MHz, the kind of noise routinely generated by consumer electrical and electronic equipment. Interestingly, the magnetic component of this electromagnetic noise is a thousand times weaker than the lower exposure limits adopted in current World Health Organization (WHO) guidelines, yet it can disrupt the function of an entire sensory system in a higher vertebrate. The birds regain the ability to orient to the Earth's magnetic field when they are shielded from electromagnetic noise in the frequency range from 2 kHz to 5 MHz or when tested in a rural setting.