In the Pisa experiments, Gagliardo, working with Martin Wild of the University of Auckland , followed up experiments done in 2004, which showed that pigeons could detect magnetic fields. She argued that this did not mean they actually did.
So in 24 young homing pigeons she cut the nerves that carried olfactory signals to their brains. In another 24 pigeons she cut the trigeminal nerve, which is linked to the part of the brain involved in detecting magnetic fields. The 48 birds were released 30 miles from their loft. All but one of those deprived of their ability to detect magnetic fields were home within 24 hours, indicating that it was not an ability that helped them to navigate. But those who had been deprived of their sense of smell fluttered all over the skies of northern Italy. Only four made it home.